There is an accumulation of experimental data supporting the concept that many classes of biological pest management are effective in controlling diseases caused by soilborne pathogens. The mode of action of many of these treatments has been described. The volatile compounds released from Brassicas are known to release biocidal compounds that are able to suppress soilborne pathogens when incorporated into the soil (Kirkegaard, 1998). Composted amendments can introduce a varied microflora into soil ecology, including many biocontrol agents, while providing a suitable substrate to support their growth (Hoitink, 1999). Solarization has also been shown to reduce pathogen propagule numbers by elevating soil temperatures to lethal levels and contribute to effective disease control at sub-lethal temperatures (Katan, 1991).
Sustainable control of soilborne phytopathogenic fungi is likely to be achieved through the enhancement of biologically based methods via the integration of multiple techniques (Cook, 1990). Research has indicated that a pre-plant combination of biofumigation with composted organic amendments increases the efficacy of both treatments (Cook 1993, Lyons 2001). Even sub-lethal doses of biofumigants can act to weaken pathogen propagules making them more susceptible to the actions of the microbial antagonists that can be delivered through compost applications. Similarly, the heating of soilborne sclerotia via solarization increases their chance of colonization by bacteria (Lifshitz, 1983). It is clear that a fundamental attribute of an effective integrated organic system is its ability to, firstly, decrease pathogen numbers in the soil and then establish a soil microecology suppressive to pathogens.
The viability of biofumigation to control pathogens has been investigated for many years. Two projects recently funded through the Southern SARE graduate research program successfully developed an integrated production system that combines an enhanced form of biofumigation with the many benefits of composts. The studies conducted at The University of Tennessee by doctoral students Martin Lyons and Stephanie Harvey showed that mustard seed meal has extremely high concentrations of isothiocyanates (ITCs). The seed meal is also a significant source of nitrogen and other nutrients. When incorporated into the soil, ITCs act as effective biofumigants, reducing populations of pathogenic fungal species (Sclerotium, Rhizoctonia, and Phytium), nematodes, weeds, and certain insect species (Charron and Sams, 1999).
Biofumigation is the use of volatile plant chemicals for control of soilborne pests. These products have been shown to suppress the pathogens Botrytis cinerea, R. solani, F. oxysporum, Didymella lycopersici, and Cladosporium fulvum (Urbasch, 1984). Although the fungicidal properties of ITCs have been identified since at least 1937 (Walker et al., 1937), only recently has the practice of using Brassicas for pest control been termed “biofumigation” (Angus et al., 1994). In our own studies, we found that the volatiles from several Brassica species suppressed the growth of the tomato pathogens P. ultimum, R. solani, and S. Rolfsii (Charron and Sams, 1998; Charron and Sams, 1999: Harvey, Hannahan, and Sams, 2002)
The biocidal activity of Brassicas against fungal pathogens, nematodes, weeds, and insects is frequently attributed to ITCs from Brassica tissues (Delaquis and Mazza, 1995). ITCs are effective, broad-spectrum pesticides (Mithen et al., 1986; Isshiki et al., 1992), and substantial quantities of them can be produced for field application. Research has shown that Black mustard (B. nigra L. W. Koch) and Indian mustard (B. juncea L. Czern and Coss.) produce high levels of ITC (Tollsten and Bergström, 1988) and could be utilized in a biofumigation cropping system.
Control of V. dahliae by Brassica residues has also been shown. The number of V. dahliae propagules in a 36-m2 plot incorporated with 200 kg of chopped broccoli (B. oleracea var. italica) were lower than in control plots and were comparable to plots fumigated with methyl bromide + chloropicrin (Subbarao et al., 1994).
Since 1999 field trials have been conducted at Knoxville Experiment Station. Significant decreases in the incidence of Southern Blight of tomato were recorded, as well as increases in fruit yield, when integrating biofumigation into a sustainable production system. The research yielded important knowledge pertaining to the development of the appropriate production methods utilizing biofumigation as a management technique. Both Brassica cover crops and mustard seed meal incorporations have been used. The ability to amend production soils with the spreadable meal, in conjunction with its high ITC content (3-4 x leaf tissue), give this enhanced biofumigation technique great potential. Problems associated with growing cover crops such as variable stands and weather complications are avoided when using the meal. As a fully organic product, pre-plant mustard meal applications give the grower superior ability to control soilborne pests.
Composts and Biological Control
Composts improve plant health and productivity due to enhanced soil nutrient levels and improved physiochemical properties (increased bulk density, porosity, aeration) and increased water-holding capacity (Corti 1998). Disease suppression due to the advantageous changes to the soil microbial composition, including increases in the populations of known biological control agents (Trichoderma, Bacillus, and Pseudomonas spp.), has been noted by many researchers (Hoitink 1999, Lyons 2001). Composting is an ecologically sound way to recycle organic farm wastes, such as animal manures and plant debris. It avoids the environmental hazards associated with burning, burying, or spreading these agricultural by-products on fields. These methods are not sustainable and can lead to problems such as increased particulate matter in the air, leaching and ground water pollution, and toxic excesses of phosphorous and nitrogenous compounds in the soil.
Potential problems with compost as a pre-plant treatment include using a product that has not been composted properly and, hence, is not mature. Compost testing is to be encouraged. With the assistance of extension agents and university resources maturity levels can be gauged by measuring C:N ratios and pathogen levels assessed via assays. Feedback from this type of testing can direct more effective composting methods.
Many researchers throughout the world have investigated the relationship between the addition of composts to soil and plant health. The pre-plant application of composts has many advantages. They have the ability to provide biological control of plant diseases while simultaneously improving physical soil properties and micronutritional levels (Corti, 1998). The composted material used is often derived from agricultural waste products and, hence, serves to “recycle” these voluminous compounds. Composted soil amendments act to create a suppressive environment in the soil that can biologically control soilborne pathogens through microbial competition, antagonism, antibiosis, hyperparasitism, and possibly induce systemic resistance in plants (Hoitink, 1994). In particular two types of composts will be studied, poultry waste compost (PWC) and spent mushroom substrate (SMS).
The three phase composting process ultimately leads to the recolonization of the substrate with mesophilic microflora and microfauna. (Hoitink, 1986). Microorganisms commonly found in composts include: Bacillus spp., Enterobacter spp., Pseudomonas spp. Streptomyces spp., Trichoderma spp., and Gliocladium spp. (Hoitink, 1994). Some of these species are recognized to exhibit properties of biological control.
Biological control of plant pathogens has been observed and studied for many years. As defined by Baker (1987), biocontrol is “the action of parasites, predators, or pathogens in maintaining another organism’s population at a lower average than would occur in their absence.”
Tomato Production and Blight diseases as a Model System
The use of raised-bed plasticulture methods for fruit and vegetable production is becoming increasingly prevalent within the United States. Advantages include increased crop performance by conserving moisture and nutrients, stabilizing soil temperature, reducing some diseases, reducing or eliminating weeds, and increasing early harvest yields (Jaworski, 1981). Hence, we aim to adapt this commonly used production method for commercial organic agricultural production. Often grown without rotation, tomato fields can develop high pathogen inoculum densities. Southern Blight, caused by the phytopathogenic fungus Sclerotium rolfsii, represents one of the major disease threats to tomato crops (both organic and conventional) in the southeast United States. However, this pathogen is also a threat to many other crops. Significant economic losses have been attributed to Southern Blight in tomato, green beans, cantaloupe, peppers, and potatoes grown in predominantly warm, humid seasons. The disease spreads most effectively between 25-30C. These factors make the investigation of pre-plant soil treatments for organic tomato production under pressure from Southern Blight a suitable choice as a model system for our investigations.
Various control methods have traditionally been utilized to lessen the incidence of Southern Blight in commercial vegetable fields. Control by solar heating has been successful in Israel. Studies by Elad and Katan (1980) have demonstrated that 2-4 week applications during the summer were able to reduce sclerotial numbers and limit disease. Additionally, these researchers demonstrated that combining solar heating with applications of Trichoderma harzianum was more effective than either treatment alone. Punja (1985) contended that by altering the composition or activities of soil microflora, including the addition of biocontrol agents such as antagonistic microorganisms, that there is a potential for disease control. T. harzianum, which has been described as a destructive mycoparasite that competes aggressively against other soil fungi, is acknowledged to suppress Southern Blight when introduced to field soils (Jenkins, 1986). The growth of the biological control agent T. harzianum is enhanced with solar heating (Jenkins, 1986).
The Growth of Organic Agriculture
In October of 2002 the USDA fully implemented the National Organic Program Standards (NOPS). The result is a clarification of the certification for organically farmed produce. Consumers will be able to easily identify produce grown via organic methods and have confidence in their purchases. Even though there has been a steady increase in demand for organic produce, it is likely that consumption will increase markedly because of the certification.
Already identified as being the fastest growing agricultural sector, these recent changes represent an opportunity for regional farmers to view organic farming as a potentially profitable alternative to traditional, non-sustainable crop production (Koenig, 2002). Successful modern organic farming strives to be farmer-oriented, multidisciplinary, system-oriented, with a whole-farm perspective (Lockeretz, 2000). The USDA has identified certain non-synthetic biological disease management inputs as being necessary for aggressive pathogen control. The use of botanical, or plant-derived compounds, are recognized. Biofumigation is such a method.
The USDA standards also recognize the benefits of applying mature, well-produced composts in preference to raw animal manures. In order to assist organic growers with the development of reliable, high-yielding production systems research is required on the effective utilization of biofumigation, composting and other sustainable farming methods. Important components to our project are the studies pertaining to soil health in organic systems. Identifying soil microbial community profiles that are linked with disease suppression has also been recognized as a priority area of investigation by the USDA (Koenig, 2002). The dynamics of organic farming systems is an area of research that has been neglected in the past, however, it now represents an area of significant potential income in many southern states.
Hypothesis of the study
Considering scientific findings reviewed above and potential positive interactions of biofumigation and compost, we hypothesized that the combination of mustard meal applicaiton with compost might improve biological characteristics of the soil if compared with the incorporation of mustard meal along or chemical fumigants and stabilize these positive characteristics with time. The improvement of soil health will lead to a decrease of plant diseases and to an increase of the plant yield.
Objectives of the project were:
1) Test the effect of biofumigation (cover crop, different rates of mustard meal and compost application) on tomato yield, quality and disease development in the field experiments at different locations.
2) Determine long-term influence of mustard meal and compost treatments on strawberry yield, quality and disease in the field experiment.
3) Evaluate different techniques of MM application and timings of compost incorporation
4) Test the effect of biofumigation (cover crop, mustard meal and compost application) on bacterial and fungal characteristics of the soil and nematode population in the field experiments and commercial sites at different locations.
5) Test the effect of biofumigation (rates of MM and compost application) on weeds suppression.
6) Validate the optimal combinations of mustard meal and compost in experiments with commercial growers.
7) Develop a database of the collected information and present results of the project at the webpage “Enhanced Biofumigation & Composting”
The effects of different combinations and techniques of mustard meal and compost application and chemical fumigants on vegetable production are studied in four field experiments in Tennessee and North Caroline and in three on-farm trials with commercial growers during 2003-2005. Yield and quality of tomato and strawberry plants and their diseases were measured to characterize the effects of enhanced biofumigation on productivity. Biological characteristics of soil including number of heterotrophic bacteria, fungi, nematode population and structure were measured twice per year in two filed experiments during 2004 and 2005 to reveal the influence of biofumigation on soil biology. A database was developed to consolidate all the experimental information on the effects of enhanced biofumigaiton and composting in vegetable production and to facilitate the statistical analysis. It was found that combination of mustard meal incorporation with compost increased the yield and quality of tomatoes and protects tomato plants from Early Blight. These positive effects were achieved after 1-2 years of the enhanced biofumigation and composting. Mustard meal application also increased the yield of strawberry plants and protected them against Anthracnose. Biological assays of soil in the experiments showed that the application of mustard meal disturbed the bacterial and fungi populations in soil during the first two weeks after mustard meal applications. Statistically significant negative effects of mustard meal application on number of fungi and heterotrophic bacteria were found in two weeks after treatments in the experiment at Knoxville, TN. A positive effect of the mustard meal on the microbial populations was at some treatments in the experiment at Fletcher, NC. However, to the end of the growing season the bacterial and fungi population is stabilized and deceased in number in both experiments indicating self-regulating ability of the microbial population. The response of nematode population and structure to mustard meal and compost application depended on soil and weather conditions. Mustard meal treatment and basamid treatment statistically significantly decreased the number of spiral nematode in soil associated with damage to some crops. Oil Radish treatment presented the best values for marketable yield and fruit dry weight in the on-farm trial. Additional experiments with compost treatments are needed to check on the accumulative effect of compost and oil radish on vegetable production. The main experimental results obtained in the project were presented to scientific community and producers at several meetings and field days. A webpage “Enhanced Biofumigation & Composting” was established to inform farmers, growers, agents and scientific community on the objectives of the project, established experiments and main findings. The webpage intends to promote the enhanced biofumigation to producers and to give practical recommendations on the technique. The web address is http://web.utk.edu/~tkarpine/EnhBiofum.html.
The study was conducted as a part of SARE project “Enhanced Biofumigation and Composting” initiated in 2002 and included four field experiments at three locations described below.
Tables and Figures mentioned in this report are on file in the Southern SARE office. Contact Sue Blum at 770-229-3350 or email@example.com for a hard copy.
1. Field experiment with tomato plants at Fletcher location (will be referred as Fletcher-tomato experiment).
This experiment was established in the fall of 2002, at the Mountain Horticultural Crops Research Station, Fletcher, NC. The goal of the experiment was to determine long-term (3 years) influence of compost material and mustard meal applications on disease suppression and productivity in tomato cropping system. The scheme of the experiment included 6 treatments in 4 replicates (Table 1). The size of each plot was 35x5ft2.
Preplant fertilizer was broadcast as ammonium nitrate and muriate of potash prior to bed formation. Beds were formed and mustard meal and compost were applied to the top of the bed and were then tilled into the top 4 inches of soil. Then plastic mulch, drip irrigation and Telone C-35 (where appropriate) were applied one operation. The beds were then irrigated for 8 hours. Tomatoes (were planted in a single row through the plastic mulch on June. In about two weeks (middle of July) fertigation was initiated. Six tomato plants were harvested from each plot and graded biweekly during August and September.
2. Field experiment with tomato plants at Knoxville location (will be referred as Knoxville-tomato experiment).
The experiment was established in the fall of 2003 (a year later than the experiment at Fletcher location), at the Knoxville Agricultural Experimental Station (Tennessee) on the lower terrace of the Tennessee River. The soil is classified as a fine-loamy, siliceous, thermic Typic Hapludult (Hartgrove et al., 1993). The goal of the experiment was to test the effect of cover crop, mustard meal and compost application on tomato yield, quality and disease incidence. The scheme of the experiment included 9 treatments in 4 replicates (Table 1). The size of each plot was 25×4 square ft. All plots were limed before the experiment to raise pH to 6.5-7.0. ISCI.20 Brassica variety was used on all Brassica treatments. Brassica was seeded at 18 g per plot. Control plots and alleys between replicates were seeded with rye. Treatments were incorporated in late March except compost with following irrigations (1 inch at the first day and then 1 inch in two days). Black polyethylene mulch and 8 mm drip irrigation line (from T-TAPE, model 508-12-450) was laid onto the field along each replicate at the beginning of May. After that tomato plants (Mountain Fresh variety) were transplanted into plots (14 transplants at each plot). Yield and disease information were collected from 10 plants at each plot excluding 2 buffer plants from both sides. The irrigation was applied twice a week during 4 hours at rate 0,45 gallons per minute per 100 ft. It provided about 1 inch of water per week. The irrigation didn’t depend on the frequency of rain and soil moisture. Fertilizer was applied at the fall (600 lb of 10-10-10 fertilizer per acre) and every week after planting through the irrigation system. The first two weeks after planting complex NPK fertilizer (8-16-36) were applied to provide 13 lb/acre of nitrogen, 26 lb/acre of P and 58.5 lb/acre of K per week. The following weeks KNO3 (13,7% of N and 46,0% of K) and CaNO3 with 15,5% of N were applied in turn to provide 7 lb/acre of N and 7 lb/acre of K per week.
Harvest data were collected from each plot (per 10 plants). Fruits were graded by size (Florida scale, tray sizes 4X5, 5X6 and 6X6). Weight and number of fruits were recorded for each grade as well as the number and weight of the diseased fruits.
3. Field experiment with strawberry plants at Knoxville location (will be referred as Knoxville-strawberry experiment).
The experiment was established in the fall of 2003 (a year later than the experiment at Fletcher location), at the Knoxville Agricultural Experimental Station (Tennessee) on the lower terrace of the Tennessee River. The soil was the same as in the Knoxville-tomato experiment. The goal of the experiment was to test the effect of cover crop, mustard meal and compost application on tomato yield, quality and disease incidence. Different time of compost application (before and after MM application) and covering with plastic (immediately after MM application and 3 weeks after) were investigated. The scheme of the experiment included 9 treatments in 4 replicates (Table 1). Size of each plot was 96 square ft (16 ft by 6 ft). Treatments were incorporated each year in April. After that strawberry plants (Chandler variety in 2004 and Bish and Sweet Charlie in 2005) were transplanted into plots (32 transplants at each plot). Yield and disease information were collected from 28 plants at each plot excluding 2 buffer plants from both sides. The irrigation was applied twice a week during 4 hours at rate 0,45 gallons per minute per 100 ft. It provided about 1 inch of water per week. The irrigation didn’t depend on the frequency of rain and soil moisture. Fertilizer was applied at the fall and every week after planting through the irrigation system. Harvest data were collected from each plot (per 28 plants). Weight and number of fruits were recorded.
4. Field experiment with strawberry plants at Nashville location (will be referred as Nashville-strawberry experiment).
The experiment was established in the fall of 2003. The objective of the experiment was to evaluate the effect of a high rate of mustard meal application (4000 lb/acre) on the production of strawberry daughter plants. The experiment had two treatments (Control and MM application) and 4 replicates. Number of daughter plants and their vigor (rating 0-10) were characterized in 2005.
5. Disease and weeds count
The infection of each plot with Early Blight and Southern Blight in the experiments with tomato plants was count weekly after the first manifestations of the diseases. The infection of tomato plants with Early Blight was estimated every year as the percentage of affected leaf area in the Knoxville-tomato experiment and using the Horsfall-Barratt Disease Rating System. The rates were from 1 (0% disease) to 12 (there is no disease free tissue at all). The infection of tomato plants with Southern Blight was estimated as the number of diseased plants at each plot. Vigor rating was implemented in both tomato and strawberry experiments. Rating scale for strawberry plants was from 1 to 7, where 1=all plants dead, 2=majority plants dead, 3=poor stand, 4=Fair Stand, 5=Good, 6=Very Good, 7=All Healthy. Rating scale for tomato plants was from 1 to 5, where 5 was the best vigor. Rating of Antrhacnose on strawberry plants was made in 2004. Rating Scale included 7 points: from 1 (all plants dead) to 7 (all plants healthy). Weeds count was done in the fall 2003 at the Knoxville-strawberry experiment. Number of the following weeds were estimated: Broadleaf, Grass,Onion, and Nutsedge.
6. Fungi and Bacterial Soil Assay
Soil samples were collected from the 0-to 15-cm soil depth three times per year. First sampling was before MM incorporation, second sampling was 2 weeks after mustard meal incorporation and the third one was then after harvest. The general bacterial assay was made to represent the total bacterial population of heterotrophic bacteria as described by Martin (1975). The Pythium counts were made to characterize potential infectivity of soil for tomato root rot caused by this fungus. The general fungal assay was conducted by serial dilution, as with the bacterial counts. Since fungi are not as numerous as bacteria, aliquots were removed from the solutions for plating on the fungual medium at lower dilutions than for the bacterial medium. The fungal medium was potato dextrose agar plus 0.1% streptomycin sulfate. In both cases plates were incubated for 2 days at room temperature before counting. In the Results section Bacterial counts represent population densities of heterotrophic bacteria measured by 10E-6 CFU per g of dry soil (Colony FormingUnits per 1 gram). Fungi counts represent population densities of fungi measured by 10E-4 CFU per g of dry soil. Pithium counts represent population densities of Pithium measured by 10E-3 per g of dry soil.
2.3. Statistical analysis
A relationship database was developed to facilitate the analysis and the exchange of the information collected in the experiments. The database was comprised of 11 tables described in the Table 2. The tables are populated with the results of the experiments according to the description. Relationships between tables of the database are presented in Figure 1. The database was developed in Access.
The collected data on fungal, bacterial, nematode assays, disease development and yield (total fruit weight and number, weight and number of fruits of each grade) were subjected to ANOVA to indicate the effect of treatments on the development of disease, biological properties of soil, tomato and strawberry yield and its quality. In addition, the pair correlation coefficients, Spearman rank correlation coefficients and the partial correlation coefficients among mean total fruit yield, mean percentage of leaf damage, bacterial and fungal counts at the plots of the experiment were calculated to characterize relationships among these parameters and the effect of soil biological characteristics on the disease development and yield. Spearman rank correlation coefficients were used, to avoid outliers in the assessments of Early Blight development as percentage of leaf damage. This ranking replaced the use of disease rating scale at the experiment at Knoxville. The linear regression analysis was performed to fit a line through a set of changes in nematode, fungal, and bacterial counts considering initial values of these parameters as independent variables. SAS software and Excel data analysis tool were used to implement the statistical analyses.
These effects were studied in the Experiment at Knoxville Agricultural Experimental Station in 2004 and 2005. In this experiment two timings of compost incorporation were compared. First one is the incorporation of compost at the same time as MM. The second one is the incorporation of compost in 3 weeks after the MM treatments. In addition to rates of MM, two different techniques of MM application are compared. The first one is the immediate covering with plastic and the second one is just water sealing of MM treated soil. Scheme of the experiment is given in the Table 1 of the section “Materials and Methods”.
1. Effect of MM and compost application on strawberry yield and berry size in 2004 and 2005.
The results of this study are presented in Figures 5, 6 and 7. In 2004, there was a statistically significant increase in the total yield of strawberry after mustard meal application at 2000 lb/acre and immediate covering with plastic if compared with the treatment 1 (control), treatments 9 (Mustard meal and compost), 10 (Mustard meal 2000 water seal). Treatments 2, 4,5,6,7, 8 showed an increase in the yield, though it was not statistically significant. The average increase in the yield of strawberry after the treatments with the mustard meal was about 12% from the control treatment. At the first year, treatments with the combined application of the mustard meal and compost didn’t show better results than the application of mustard meal or compost along. Average size of berries is also affected by treatments in 2004 (Figure 6). Treatments 3,4,5,6,7, 8 showed statistically significant increase in the size. The average increase of the berry’ size at the treatments with the mustard meal application was 7%.
In 2005 (the second year of the experiment), the effect of MM and compost application on strawberry yield and size was not consistent with the first year. Statistically significant increase in the yield is identified only after application of mustard meal (2000 lb/acre) and compost (30 t/acre) if compared with the treatments 1, 2, 10, and 5 (1-control, 2,10-mustard meal 1000 and 2000 lb/acre, 5-compost 30 t). This treatment had water seal instead of immediate covering with plastic. All the treatments with the application of mustard meal showed an increase in the total strawberry yield (an average increase was 17%). Though, this effect was not statistically significant because of high variability of the yield in the experiment. The reason of the significant effect of the combined application of mustard meal and compost at the second year may be the same as in the experiments at Fletcher and KES with the tomato plant. The increase in the yield after MM and compost treatments was accompanied by the decrease in the average berry’s size. Treatments 5 (compost 30 t/acre), 6 (mustard meal 2000 lb/acre and compost with immediate covering, 8 – mustard meal 4000 lb/acre and compost with immediate covering) showed statistically significant decrease in the average berry’s size if compared with the control treatment. There was also statistically significant difference between treatments 4 (mustard meal 4000 lb/acre) and 5 (compost 30 t/acre). Average decrease of the size was about 7% at the treatments with the mustard meal application. This effect is inconsistent with the positive effect of the MM on the berry’s size in 2004. It may be explained by difference in varieties planted in 2004 and 2005 (Chandler vs. Sweet Charlie in 2005).
The dynamic changes in the yield of strawberries in 2004 and 2005 are presented in Figure 7 (a and b). Though the total yield of strawberry was increased at some treatments with mustard meal and compost application in 2004 and 2005, this difference was distributed randomly during the harvest period. No difference was found in the dynamic changes of the yield between treatments.
2. The effect of MM and compost application on disease of strawberry.
Anthracnose of strawberry was observed in the experiment in 2004. Rating of the anthracnose (Figure 8) showed statistically significant protective effect (P<0.05) of the MM incorporation at the rate 2000 lb/acre on the incidence of the disease. Treatments with the low rate of MM application (1000 lb/acre), with the compost application and with the combined application of the compost and MM also indicated some protective effect. Though, it was not statistically significant. Disease incidence in the treatments of the experiment correlated with the plant vigor (R=0.50, P<0.05). Rating of this parameter also showed statistically significant effect of the MM application (rate 2000 lb/acre) (Figure 8). Total strawberry yield also correlated with the plant vigor (R=0.69, P<0.05). But the correlation of the anthracnose ratings with the total strawberry yield was low (R=0.21, P>0.05) At the next year of the experiment pesticides were applied to prevent the development of the disease development.
3. The effect of MM and compost application on number of weeds.
The effect of MM and compost application on number of weeds (Broadleaf, Grass, Onion, Nutsedge) was studied in the fall 2003. The results are presented in Table 5. It was found that weed ratings in some treatments with MM may increase the number of weeds. Specifically, a statistically significant increase in the number of Grass weeds was obtained in the treatment with the highest rate of MM (4000 lb/acre). A statistically significant increase in the Broadleaf weeds was in the treatments with water seal (MM application along and MM and compost combined application), if they are compared with plastic covering. In combination it resulted in a trend to an increase of the total number of weeds in the treatments with water seal (treatments 9 and 10) and with the highest rate of MM (treatment 4) if compared with the control. The other treatments didn’t show difference with the control. The positive effect of mustard meal treatments on number of weeds may result from the improved soil conditions for plant growth imposed by the treatments. Total yield of strawberry and average berry’s size in the treatment 4 was also larger than in the control (Figures 5 and 6).
4. The effect of high dose of MM on the production of strawberry daughter plants.
This effect was evaluated in the “Nashville strawberry” experiment in 2004 and 2005. The objective of the experiment was to evaluate the effect of a high rate of mustard meal application (4000 lb/acre) on the production of strawberry daughter plants. The experiment had two treatments (Control and MM application) and 4 replicates. Number of daughter plants and their vigor (rating 0-10) were characterized in 2005. There was an average increase in the vigor and a decrease in the number of daughter plants (by 2 plants) in the treatment with MM application. But the effect was not statistically significant.
In conclusion, mustard meal application increases the yield of strawberry plants and protects them against Anthracnose. These positive effects may accompanied by an increase in the number of weeds.
1. The highest yield and quality of tomatoes was at the treatment with combination of mustard meal application with compost during the second and the third years of the field experiments.
There was no significant difference among the treatments for tomato yield in the first year the biological amendments were applied. This result was reproducible in both experiments with tomato plants, in spite of difference in soil and weather conditions and in timing of the compost application (at the same time with the MM application at Fletcher and in the fall before the MM application at Knoxville).
Table 3 demonstrates the effect of treatments in the experiments in 2004 and 2005. A significant difference (P<0.05) in tomato yield was observed among treatments only during the third year of the experiment at Fletcher location and during the second year of the experiment at Knoxville location. The highest tomato yield in both experiments was at the treatment with combination of mustard meal and compost (Figure 2 and Figure 3). Total tomato yield in the experiment at Fletcher was significantly higher (P<0.05) at this treatment and also at the treatments with the highest rate of the mustard meal along (treatment 5) and with the compost alone (treatment 3) if compared them with the control. The increase in the total yield after the application of MM and compost was 55% to the control. In the Knoxville experiment total tomato yield at the treatment with the combination of mustard meal and compost also was significantly higher (P<0.05) if compared with the control and mustard meal application at low rate. The increase of the total yield of tomato was 62% to the control. Though the effect of MM was not significant at the fist year of the experiment at Knoxville, all the treatments with the mustard meal incorporation (treatments 5,6,7,9), which included three different rates and the combination of mustard meal with compost, increased the yield of tomato. An average increase at the treatments was by 36%. This increase was not as high as at the second year, therefore a variability of the yield in the experiment didn’t allow us to accept the positive effect as statistically significant. Similar result was observed in the experiment at Fletcher location. In 2004, the maximum yield was obtained at the treatment with mustard meal and compost application. Though this difference was not significant, the increase in the yield to the control was 12%.
In both experiments the yield of jumbo tomato and extra large tomato correlated with the total yield (P<0.05) (Table 4). Treatments revealed the same pattern as for the total yield, i.e. maximum yield of these tomatoes was at the treatment with combination of mustard meal and compost. Medium size, small and cool tomato didn’t correlate with the total yield and didn’t show significant difference among the treatments (P<0.05). These results indicate that the treatments affected not only yield but also the quality of tomatoes. The application of mustard meal and compost increased the yield by increasing jumbo and X-Large tomatoes, i.e. a marketable constituent of the yield. The treatments didn’t affect yield of medium, small or cull fruit.
2. Combination of mustard meal application with compost protected tomato plants from Early Blight.
In both experiments counts of the Early Blight had significant (P<0.05) negative correlation with the total yield of tomatoes (Table 2) indicating the effect of plant damage from the disease on the total yield of tomatoes. In the Fletcher experiment, counts of the Early Blight was by about 8-11% less in the treatment with the mustard meal and compost if compared with the control in 2004 and 2005 (Table 3). Though, this difference was not statistically significant. In the experiment at Knoxville, there was a statistically significant protective effect against Early Blight in 2005 in the treatments with the compost application along and with mustard meal and compost combined application (Figure 4). The treatments showed a decrease in the damage of the plants by 60-80% to the control. Considering the negative correlation of the disease counts with the total tomato yield, we can suggest that the considerable increase in the yield, which was observed in the treatment with mustard meal and compost application in 2005 (Figure 3), may be caused by a higher resistance of tomato plants the Early Blight disease after this treatment.
Counts of the Late Blight were not statistically different between treatments at both experiments (P<0.05).
1. The effect of biofumigation and composting on Pithium population in soil
Pithium counts were made in soil samples collected after harvest in 2004 and 2005 in the experiment at Fletcher location and in 2005 in the experiment at Knoxville location (tomato). Significant increase in the Pithium counts was found in 2004 in the treatment with the application of compost along after harvest. The application of the compost in combination with mustard meal prevented the infection in 2004 (Figure 9). In 2005, however, the protective effect of mustard meal was absent. Both treatments with the compost application (along and with mustard meal) had a tendency to increase pithium counts after harvest. There was no statistically significant difference in the pithium counts after harvest in the experiment at Knoxville location.
2. The effect of biofumigation and composting on Fungi population in the experiments at Fletcher and Knoxville locations.
Soil fungi are found primarily in the top 4-6 inches of soil and are most abundant in well aerated soil. Though some fungi are pathogenic to plants, many of them contribute to soil fertility by breaking down organic compounds and by improving soil structure (Coleman and Crossley, 1996). The effect of mustard meal and compost application on number of fungi in soil in two weeks after the treatments and after harvest was studied in 2004 and 2005 at Knoxville and Fletcher location. The main results of this study are presented in Figures 10 and 11. At Fletcher location (Figure 10, a), the application of compost along had a tendency to decrease the number of fungi in soil in two weeks after the treatment by 40-60% averaged. Though, this effect was not statistically significant, because of high variability of fungi among replicates induced by the treatment. Compost was applied at the same day as mustard meal in this experiment. The application of high dose of mustard meal gave an opposite effect on number of fungi significantly (P<0.05) increasing its population in two weeks after the treatment. This effect was especially high (185% increase) in 2004. To the end of the season, however, the population of fungi is stabilized and decreased in number by 13% in 2004 and by 80% in 2005 (Figure 10,b). The decrease was especially dramatic in the treatment with high dose of mustard meal. It resulted in significantly lower population of fungi at this treatment if compared with the control, telone application and compost. At Knoxville location (Figure 11, a), statistically significant difference between treatments was observed only in 2004 in two weeks after treatments. The application of basamid led to a decrease in the number of fungi by 70% (P<0.05). The same effect was observed in 2005. Though, the decrease was only by 36%, and it was not statistically significant. Most treatments with mustard meal in this experiment also decreased the population of fungi in two weeks after treatments in both 2004 and 2005. An average decrease was 36%. This effect, however, cannot be confirmed statistically, because of high variability of fungi population among replicates. Similar to the experiment at Fletcher location, the number of fungi was stabilized and dramatically decreased (by 32-34%) to the end of the season in this experiment (Figure 11, b).
The effect of mustard meal application was also studied in the experiment with strawberry at the Knoxville experimental station (Table 1 in the Material and Methods). Soil sampling in this experiment was made only once (in two weeks after the treatments). There was a tendency to an increase in the fungal counts in two weeks after application of medium and high dose of mustard meal (2000 and 4000 lb/acre). Though, the increase was statistically significant only for the dose 2000 lb/acre. This result is similar to one obtained in the experiment at Fletcher location in 2004 and 2005.
In conclusion, although treatments of the experiments introduced significant variability in number of fungi in two weeks after treatment, there was not a clear positive or negative effect of mustard meal and compost on number of fungi. A decrease in the number of fungi after mustard meal treatment took place in two weeks after treatments in the experiment with tomatoes at the Knoxville location. However, an increase in the fungi population was indicated at the same soil, (but a different field) in the experiment with strawberry and also at the experiment with tomatoes at Fletcher location in two weeks after treatment. More clear dynamic pattern in the fungi population was observed after the two weeks in both experiments. This pattern showed a significant decrease and a stabilization of the fungi population to the end of the season.
3. The effect of mustard meal and compost applications on the population of heterotrophic bacteria in soil.
The effect of biofumigation on the population of heterotrophic bacteria in soil was also different at Knoxville and at Fletcher location.
Heterotrophic bacteria require an organic carbon source and oxygen for their growth. They represent a very diverse and important cross-section of soil microorganisms. It is beloved that this diverse cross-section of soil microorganisms is a good indicator of general soil conditions. The upper 6 inches of agricultural soil generally contains between ten million and 1 billion (1 x 107 and 1 x 109) Colony Forming Units (CFU) of heterotrophic bacteria per gram of soil. A finished compost will typically contain between 1 x 107 and 1 x 1010 CFU/g. The effects of enhanced biofumigation and composting on the population of heterotrophic bacteria obtained in the study are demonstrated in Figures 12 and 13. At Fletcher location, all treatments of the experiment increased the population of heterotrophic bacteria in soil if compared with the control in two weeks after treatments (Figure 12, a). This increase was consistent in 2004 and in 2005. The highest effect was always observed for combined application of mustard meal and compost. The increase was by 154% in 2004 and by 691% in 2005 in two weeks after the application. Though, significance of the effect was confirmed statistically only in 2004 because treatments introduced high variability of the bacterial population among plots. To the end of the season in 2004, the effect of treatments was reversed. Number of the heterotrophic bacteria decreased in the treated plots and increased at the control indicating some sort of a stabilization of the population after perturbation. In 2005, this stabilization was accompanied by significant decrease in the bacterial population at all treatments (by about 70%). Only the treatment with the highest dose of mustard meal maintained a statistically significant (P<0.05).increase of the number of heterotrophic bacteria if compared with the control (Figure 12, b). The opposite effect of the mustard meal and compost treatments on the bacterial population in two weeks after the treatments was observed in the experiments at Knoxville location (Figure 13, a). Average decrease in the number of heterotrophic bacteria for all rates of mustard meal was about 40-70%. Though, this effect was not significant because of the high variability of the population at the treated plots. To the end of the season, however, the population is stabilized and decreased by about 60% at both years of the observation (Figure 13, b). Considering these results we can conclude that the application of mustard meal disturbs the bacterial activity in the soil during the first two weeks after the application. Similar to fungi population, the treatment may give both positive and negative effects on the population of heterotrophic bacteria in soil. In general, a positive effect was observed in the experiment at Fletcher location and a negative one in the experiment at Knoxville location. To the end of the growing season the bacterial population is stabilized and deceased in number. 4. Self-regulation of the populations of fungi and heterotrophic bacteria in soil and their stationary states. As it was demonstrated in the previous sections, the application of mustard meal and compost introduces significant variability in the number of fungi and heterotrophic bacteria in soil. It makes it difficult to identify a specific effect of the treatment and the direction of change. Therefore we decided to study the variability of fungal and bacterial population in more detail considering each plot of the experiment individually and combining together the results of both experiments. Analysis of the descriptive statistics of fungal and bacterial counts made at different time points during the experiments (Table 6) showed difference between the counts made in two weeks after treatment (post-treatment counts) on the one hand and the counts made before treatments or after harvest on the other. Post-treatment counts (both fungal and bacterial) in both experiments showed an increase in the statistical parameters characterized the variability including variance, standard error, standard deviation and range. Post-treatment counts also had larger deviation from the normal distribution as it is indicated by kurtosis and skewness. Pre-treatment counts and after harvest counts had less variability and were closer to normal distribution. Considering this difference we proposed that treatments with mustard meal and compost disturb equilibrium in bacterial and fungal population in the soil introducing new nutritional resources. This change in resources stimulates growth of microbes involved in their consumption during the growing season. However, the microbial boost depletes resources to the end of the season and, therefore, followed by a decrease in the population of microbes. This dynamic pattern is hold in mean values of bacterial and fungal counts at both locations during two years of the experimental observations (Table 6). To confirm a global nature of this dynamic pattern, we estimated how changes in the bacterial and fungal counts depended on their initial level in pre-treatment and post-treatment (two weeks after treatment) soil samples. Figure 14 (a) and (b) and Figure 15 (a) and (b) demonstrate significant difference in the dynamics of the bacterial and fungal population during the first two weeks after treatments (Figures 14 and 15, a) and during the subsequent period of the growing season (Figures 14 and 15, b). Changes in the bacterial and fungal counts during the first two weeks after treatments (Figures 14 and 15, a) don’t depend on the initial pre-treatment values of the counts. There is low statistically insignificant correlation between these parameters 0.10-0.37. It indicates that changes in bacterial and fungal population observed in two weeks after treatments can not be accounted for by differences in the pretreatment counts. These differences are obviously imposed by treatments in the experiments. On the contrary, changes in the bacterial and fungal counts after two weeks (Figures 14 and 15, b) strongly depend on the post-treatment levels of the counts created by treatments. The higher level of the bacterial or fungal count was created by a treatment, the larger negative change is observed to the end of the growing season. There were almost perfect statistically significant linear relationships (more than 99% confidence level) between the post-treatment bacterial and fungal counts and subsequent changes of the counts during the growing season (Table 7, Figures 14,b and Figure 15, b). Squares of the Pearson’s correlation coefficient presented in the table indicate that from 60 to 99% of the variability in changes of the Bacterial and Fungal counts may be attributable to differences in post-treatment counts created by mustard meal and compost application. Slopes of the regression line (coefficient “a” in the Table 7) were constant and equal to about -1.0 for both bacterial and fungal counts. This value didn’t depend on location of the experiment and a year of the observations. Difference among “a” coefficients was not statistically significant for all regressions (Table 7). It indicates that only one parameter (coefficient “b” in the Table 7) may actually predict changes in the bacterial and fungal counts during the growing season. This coefficient in the regressions represents the intersection of the lines with the ordinate axis, i.e. it is equal to the post-treatment value of bacterial or fungal populations that doesn’t change during the growing season. As far as it retains constant, this value may be considered as a stationary level of the count. We will refer to this value as the Stationary State Count or SSC. The obtained regressions allow one to predict changes of bacterial and fungal counts after perturbations imposed by mustard meal and compost application and probably by any other amendment or environmental influence affected the availability of resources for microbes. If the incorporation of the amendment creates a post-treatment bacterial/fungal count in the soil that is larger than the bacterial/fungal SSC then we can predict a decrease in the bacterial/fungal population during the growing season. This decrease will be equal to difference between the post-treatment bacterial/fungal count and the SSC. If the incorporation of the amendments decreases the bacterial/fungal population below the SSC then we can predict a subsequent increase in the counts and the restitution of the stationary state value of the counts to the end of the growing season. An interesting observation can be made about stationary state values (SSC) of bacterial and fungal counts (Table 7). There was no statistically significant difference between stationary state values of fungal counts between the experiments and yeas of observations. The average fungal SSC measured in 104 CFU g-1 at the end of the growing season was 1.23. It means that any external perturbation of the population of fungi by soil amendments will be followed by restoration of the stationary state level of population of fungi that is characterized by the fungal count to be equal 1.23 for the considered soil. There was no statistically significant difference in the stationary state values of bacterial counts in the experiment at Knoxville location in 2004 and 2005. The average value of the SSC was 5.2 106 CFU g-1. Soil at this location restored this value of the after the incorporation of amendments. At Fletcher location, there was statistically significant difference in the bacterial SSC. In 2005, the stationary state level was significantly less than in 2004. This difference may result from different weather conditions during the growing seasons in 2004 and 2005. Weather conditions may change the availability of nutritional resources for microbes and, therefore, lead to a decrease/increase of the SSC in the soil. In conclusion, the population of fungi and heterotrophic bacteria in soil is self-regulated. The perturbations of the populations induced by the application of compost and mustard meal in the experiments were quickly compensated by a boost of the microbial activity. It was accomplished by a restoration of the same stationary state levels of the populations at all treatments to the end of the growing season.
The effect of mustard meal and compost application on number of total nematodes was studies in 2003, 2004 and 2005 in the experiment at Fletcher location and in 2004 and 2005 in the experiment at Knoxville location. Soil samples were analyzed before treatment (referred as pretreatment), in two weeks after treatment (post-rearmament) and after harvest (final). Structure of the nematodes population was studied in 2005 in postreatment and final samples. The analysis included the number of following groups of nematodes: Reniform, Root-knot, Spiral, Lance, Lesion, Dagger, Stubby-root, Stunt Ring, Soybean Cyst Nematode (SCN), Bacterial, Fungal, and Predator.
1. The effect of mustard meal and compost application on number of total nematodes in 2003 and 2004.
Analysis of total number of nematodes in 2003 and 2004 showed no significant difference between treatments (P<0.05) in the number of nematodes before treatments, after treatments and in the difference (number of nematodes after treatments minus number of nematodes before treatments) in the experiment at Fletcher location.
At Knoxville location (tomato), a statistically significant differences was found in the number of nematodes in 2004 (Table 8). There was an increase in the population of nematodes (P<0,05) after combined application of mustard meal and compost (treatment 9) and in the third treatment of the experiment (Brassica+Bazamid at 175 lb/acre).
2. The effect of mustard meal and compost application on structure of nematode population in the experiment at Knoxville location.
Analysis of the structure of the nematode population in 2005 allowed us to identify differences in the number of different groups of nematodes imposed by treatments in the experiments.
In the experiment at Knoxville location statistically significant differences between some treatments were identified for total nematodes, Spiral nematodes, Bacterial feeders, Fungal feeders and Reniform nematodes. Root-knot and Lance nematodes were found only in the individual plots. The rest studied groups of nematodes including Lesion, Dagger, Stubby-root, Stunt, Ring, and SCN nematodes were not found at all in the soil of the experiment. Total number of nematodes increased in the soil of this experiment in post-treatment samples in all treatments of the experiment if compared with the control (Table 8, Figure 16, a). Different groups of nematodes, however, indicated different responses to treatments of the experiment. They will be considered below in more detail.
Spiral Nematodes showed a statistically significant difference between the Control treatment and treatments 3 (Brassica (spring incorporation) +basamid 175lb/acre ) and treatment 6 (Mustard meal 1000lb/acre), and also between treatments 3 and 5(Mustard meal 500) and 5 and 6 (Table6; Figure 16, a). All mustard meal (except low dose) and compost treatments decreased the number of the nematodes if compared with the contro. Spiral nematodes have been associated with damage to bluegrass and Bermudagrass. They also contribute to stress on corn, soybeans, and other rowcrops during hot, dry weather but rarely cause yield loss even at high population levels. On clovers and other perennial forage crops, population of these nematodes sometimes reaches high levels and can cause stand decline and yield loss. Therefore a decrease in the number of these nematodes after treatments indicates a protective effect of the biofumigation for aforementioned crops. In conclusion, mustard meal treatment and basamid treatment decrease the number of spiral nematode in the soil. The maximum effect of mustard meal was at 1000lb/acre.
Bacterial-feeders generally were increased in the soil in two weeks after the MM and Compost application at all treatments (Table8; Figure 16, a). A statistically significant increase was found in the treatment 7 (MM2000) if compared with the control treatment and with the Brassica incorporation (Trt.2). The observed effect may result from the increase in the density of bacterial population indicated in the previous sections. Bacterial-feeders are considered as a beneficial functional group of nematodes. They help to balance total bacteria populations and release nitrogen back to the plant. It was reported that bacterial feeders actes as a compensatory factor to plant-parasitic nematodes in ecological function (Neves & Huang, 2005). They also a very important part of the root protection, one which most agricultural soils lack. It is believed that bacterial-feeders are important in preventing root-feeding nematodes from finding the roots of plants. In conclusion, the application of mustard meal increases the number of nematodes that consume bacteria.
Fungal-feeders can reduce total levels, including root rot fungi, and also help release the nitrogen locked up inside fungi back to the plant. This group of nematode showed the most significant increase in the treatment 2 (after brassica incorporation) (Table 8). This effect is in agreement with the finding of Gomes et al. (2003). It was reported that the population of fungal feeders increased at the final growing cycle of soybean because the root tissue was in decomposition. Visa versa, basamid treatment (tr.3), mustard meal 1000 (tr.6) and compost (tr.8) decrease the number of these nematodes. As the result statistically significant differences were indicated between tr. 2 and treatments 3,6,8. The effect of basamid on a decrease in the number of fungal-feeders was especially strong. Therefore statistically significant differences were found between this treatment and treatments 4 (Brassica (fall incorporation) + mustard meal 1000 lb/acre (spring incorporation)); tr. 5(Mustard meal 500 lb/acre) and tr. 9(Compost + Mustard meal 1000 lb/acre). Interestingly, the combination of mustard meal (1000) and compost statistically significantly increased the number of fungal-feeders if compare with only mustard meal application. In conclusion, brassica incorporation increases the number of nematodes that feed on fungi, probably, because of increased number of fungi after this incorporation. Mustard meal, compost and, especially, basamid application decrease the number of the fungal-feeders. The suppressive effect is absent if mustard meal is incorporated in combination with compost.
Reniform nematodes showed statistically significant difference between Tr.9 (compost + mustard meal 1000 application) and most other treatments including Trs 1,2,3,4,5,7 (Figure 16, a). The reason of this effect is not clear. According to our previous studies the treatment of mustard meal in combination with compost is the most effective. It gives the highest protection of tomato plants from Early Blight and the highest yield. Therefore the increase of reniform nematodes after this treatment causes alarm. Life cycles of the nematode can be very short under ideal conditions; an egg may hatch and develop into an egg-laying adult in as little as three weeks. The short life cycle can lead to a very rapid buildup of this nematode. Fallowing land is not as effective for controlling reniform nematode as it is in controlling other nematodes, because reniform nematodes can survive for longer periods in air-dried soil than other nematodes. This also increases the possibility of spreading the nematode to uninfested areas. Unlike most other nematodes, which tend to be highly aggregated, reniform nematodes can be distributed almost evenly through a field. When this happens, yield losses are uniform across the field and may be difficult to detect. Plants susceptible to reniform nematodes include soybeans, cotton, tobacco, sweet potatoes, and many vegetables, ornamentals and weeds. Corn and peanuts are very poor hosts and small grains, sorghum and common bermudagrass are non-hosts. Therefore management may include rotation with non-host or poor host crops (corn or peanuts), nematicides, and weed control. In conclusion, the application of compost in combination with mustard meal (1000 lb/acre) statistically significantly increases the number of reniform nematodes.
To the end of the season, the number of all groups of nematodes was decreased (Table 8; Figure 16, a). Statistically significant difference was found only for spiral nematodes and bacterial feeders. The direction of change if compared with the control was reversed to the one observed in two weeks after treatments. Spiral nematodes were increased in number in the treatments with mustard meal and compost. Bacterial feeders were decreased at these treatments. The indicated dynamics implies some sort of self-regulation among different groups of nematodes.
3. The effect of mustard meal and compost application on structure of nematode population in the experiment at Fletcher location.
I the experiment at Fletcher location in 2005 statistically significant differences between some treatments were identified only in post-treatment soil samples for total nematodes, bacterial feeders, and fungal feeders (Table 9, Figure 17). The population of these groups of nematodes and total number of nematodes decreased in all treatments of the experiment if compared with the control. The most significant decrease was after mustard meal treatment and after combined application of mustard meal and compost. There was statistically significant effect of mustard meal treatments (both rates) and combination of mustard meal with compost on number of total nematodes (Table 9). The number of total nematodes at these treatments was increased by 60-80%. The effect was definitely provided by the meal, because compost along was not effective.
The effect of mustard meal and compost treatment on number of bacterial-feeders and fungal-feeders recapitulated the effect of treatments on number of total nematodes (Figure 17). The effect of mustard meal at rate 16 lb per plot decreased the number of bacterial-feeders by 93%, rate 8 lb per plot – by 83% and compost and mustard meal application – by 67%. The decrease in the number of fungal feeders was by 94%, 96%, and 92% accordingly. Root-knot, Stunt, Ring and SCN nematodes were found only in the individual plots of the experiment. The Lesion, Dagger, Stubby-root, and Lance nematodes were not found at all. If compared with the experiment at Knoxville location, the number of nematodes generally increased to the end of the season.
4. Dynamics and self-organization of nematode population in soil.
Nematode damage caused to yield depends on the pathogenecity of the nematode species in soil and nematode population density at planting. Therefore, knowledge of nematode population dynamic is crucial to predict yield losses. Most models consider the yield damage is directly proportional to the nematode population density, when it is above a certain threshold (Ehwaeti et al., 2000). It is also believed that multiplication of nematodes with a single generation decreases with increasing population density at planting. Nematodes that have two of more generations in the lifetime of a crop can have a complex dynamic in their density depending on environmental factors. Though soil nematodes are potentially a good indicator of soil conditions, there is no good understanding on what factors regulate their community structure and population dynamic (Trudgill, 2001). The experimental data on total number of nematodes at Fletcher and Knoxville in 2003, 2004 and 2005 reveal an interesting regularity in the dynamic of this parameter. Namely, they demonstrate a self-organization ability of the nematode population in soil. Analysis of this regularity is considered below. It may underlie the development of a predictive model of nematode population density.
To reveal this ability we had employed the following approach. Correlation between the initial number of nematodes and their change was calculated each year considering all plots together in the experiment at Fletcher and at Knoxville. In 2003 and 2004, the total number of nematodes before treatments was considered as the initial number of nematodes. The change was calculated as difference between the total number of nematodes after treatments and before the treatments (mustard meal application). In 2005, the total number of nematodes in 2004 was considered as the initial number of nematodes. The regression analysis was applied to characterize a relationship between the initial number of nematodes and their change qualitatively. Linear equations were obtained to predict changes in the number of total nematodes with time for each experiment and each year.
Figures 18, 19 (a, b, c) present the results of the correlation and regression analysis applied to the datasets obtained at the Knoxville Experimental Station (Tennessee) and Mountain Experimental Station at Fletcher (North Caroline) in 2003, 2004 and 2005. The figures indicate that there is a significant negative correlation between the initial number of nematodes (before treatments) and their change after treatments (2-3 weeks). This correlation was very high in 2003 with the correlation coefficients to be equal 0.95 and 0.87 at Knoxville experimental station and Mountain experimental station correspondingly. In 2003 the correlation coefficients were decreased to values 0.62 and 0.64 indicating moderate relationship. Though, they remained statistically significant (P<0.001). The reproducibility of correlation between the initial numbers of nematodes and their subsequent change during the three years and at two different soils and locations allows us to conclude that this relationship represents a universal dynamic characteristic of the nematode population in the soil regulating the numbers of total nematodes. This regulation is independent on the imposed treatments. A high initial number of total nematodes in soil is always accompanied in the experiments by greater decrease after treatments than a lower initial number of nematodes. If the initial level of nematodes is very low, than an increase in the number of total nematodes takes place with time. This type of relationship between an initial value of a soil parameter and its change with time indicates self-organization ability of the soil system in respect to this parameter. It was revealed for potassium and phosphorous regimes in soil as well (Karpinets and Greenwood, 2003). In case of nematode population it may be mathematically described by a simple equation:
where Nc is the change in the number of nematodes;
Nst is the Stationary Number of Nematodes in the soil in a specific condition (temperature, moisture, available nutrients and so on);
A is a coefficient that defines the intensity of soil processes directed toward return of a steady stationary number of nematode in soil after perturbation. We will refer to this constant as the Renewal Rate.
According to this equation, a set of soil condition (physical, chemical, biological) create an environment that is optimal for a certain total number of nematodes (referred as the Stationary Number of Nematodes). And it imposes dynamic changes in the total number of nematodes to meet this new stationary level. Interestingly, the perturbations imposed by treatments of the experiments (mustard meal, compost, pesticides) don’t affect this global dynamic in the total number of nematodes. Though, they increase a scatter of data, as it is demonstrated in Figure 20. It is also plausible that the treatments affect the structure of the nematode community, for example, increase/decrease in the number of different classes of nematodes. It is known that those nematodes that feed on bacteria and fungi play an important role in soils (Bardgett et al. 1999). But the treatments in the experiment significantly affect the biomass of microbes and fungi in soils. We can speculate, therefore, that treatments in the experiments may change structure of the nematode population (ratio between different varieties of nematodes) in soil. However, these treatments don’t affect the stationary level of total nematodes. As it is demonstrated in Table 10, this parameter is probably a characteristics of the environmental conditions in the soil. Therefore, changes in the total number of nematodes will always depend on a constraint to match the number of total nematodes to a certain level determined by these environmental conditions.
The linear equations presented in Figures 18 and 19 allow us to numerically estimate characteristics of self-organization ability of total nematode population in the experiments for each year (Table 10). According to this table steady stationary number of total nematodes depends on soil type/location and weather conditions. In 2004, environmental conditions increased Nst by 6 times at Fletcher and by about 14 times at Knoxville loation. The values of Nst were always greater at Knoxville location than at Fletcher. Surprisingly, the Renewal rates (A) were almost constant for both sites and didn’t depend on environmental conditions. It allows us to speculate that this parameter is more a characteristic of nematodes as organisms than specific weather and soil conditions.
A known relationship between the main groups of nematodes in soils gives a support to the self-regulation ability of total nematode population considered above. It is known that plant parasites and bacterial feeders are commonly dominant functional groups in nematode communities (Freckman & Caswell, 1985), and these functional groups act in a compensatory manner, one increasing while the other decreased. Specifically, bacterial feeders act as a compensatory factor to plant-parasitic nematodes in ecological function (Neves & Huang, 2005). In this way, feed-back relationship between the main groups of nematodes may underlie the established stationary state levels in the total number of nematodes. The results of studies with fumigants also demonstrate high self-organisation ability of nematode population. It was found that the number of some r strategy species of nematodes can increase rapidly after treatment to levels much greater than previously (Trudgill, 2001). It was also suggested that the K strategy species can suppress the r strategy species and maintain a balance between subpopulations of nematodes. Therefore not only feed-back relationship between the groups of nematodes characterized by different nutrition, but also by different rate of propagation (a high rate of propagation on one hand and a regulated, density-dependent propagation on the other) may underlie self-organization ability of nematode population.
In summary, the presented results indicate that the number of nematodes in soil is self-regulated. Each soil under consideration was able to maintain a steady stationary level of nematode that was a characteristic of the soil and environmental conditions. Positive or negative deviations in this parameter from the steady stationary levels imposed by the environmental conditions including treatments in the experiments were recovered with time. The Renewal rate was constant in the studied soil, independent on treatments of the experiment and be influenced by only weather conditions. Considering stability of the stationary states of total nematodes in soil and their Renewal rates, we may conclude that qualitative estimation of these parameters in the soil for different weather conditions allows one to predict the dynamic changes in the nematode population after environmental perturbations.
Educational & Outreach Activities
1) The main experimental results obtained in the project were presented to scientific community and producers at several meetings and field days.
Carl Sams 2004:
A demonstration of the experiment “Control of soil-borne pests of tomato with enhanced biofumigation and composting systems” (Fletcher, NC) was made at the Tomato Field Day (08/05/04) at the Mountain Horticultural Crops Research & Extension Center. The results of the experiment were presented by Doug Sanders.
A presentation of the results was made at the Fresh Market Tomato Field Day at Mountain Horticultural Crops Research Station (August 4, 2005) by Doug Sanders and Luz Reyes, Dept. Horticultural Science, NCSU; Carl Sams and Tatiana Karpinets, Univ. of Tennessee. The title of the presentation is “Mustard meal and compost as an alternative to methyl bromide”
Results of the experiment with strawberry plants were presented to North American Strawberry Growers Association at the North American Berry Conference in Savannah, GA (January 4-6 2006). The presentation was made by Carl Sams. The title of the presentation is “Biofumigation with composting for soil borne pests”.
2) On-farm testing confirmed results of the study in three demonstration experiments: (a) at Delvin’s farm, College Grove, TN, (b) at Tannin’s organic farm, TN. and (c) at the Holden Brothers Farm, Brunswick, NC.
3) A webpage “Enhanced Biofumigation & Composting” was established to inform farmers, growers, agents and scientific community on the objectives of the project, established experiments and main findings. The webpage intends for promotion of the enhanced biofumigation to producers. The web address is http://web.utk.edu/~tkarpine/EnhBiofum.html.
4) A database was developed to consolidate the experimental information on the effects of enhanced biofumigaiton and composting on yield and quality of tomato and strawberry plants, and on biological characteristics of soil, including number of heterotrophic bacteria, number of fungi, nematode population and structure. The database is available for download at the website of the project http://web.utk.edu/~tkarpine/Results.html.
5) The following papers are now in preparation, which are based on the results obtained in project.
Combination of mustard meal and compost application increases the yield of tomato crops and their resistance to Early Blight.
The effect of mustard meal and compost applicaiton on strawberry yield, quality and disease.
Self-regulation dynamics of heterotrophic bacteria and fungi populations in soil ecosystems after perturbations imposed by application of compost, mustard meal and fungicides.
The effect of mustard meal and compost application on nematode population, structure and dynamics in soil.
The following results of the study are practically and scientifically important and will impact on sustainable agriculture.
1. Combination of mustard meal incorporation with compost increases the yield and quality of tomatoes, but the effect may be achieved after 1-2 years of the application.
2. Combination of mustard meal application with compost protects tomato plants from Early Blight.
3. Mustard meal application increases the yield of strawberry plants and protects them against Anthracnose. These positive effects may accompanied by an increase in the number of weeds.
4. The application of mustard meal disturbs the bacterial and fungi communities in the soil during the first two weeks after the application. Both, a decrease and an increase in the number of heterotrophic bacteria and fungi may take place. To the end of the growing season the bacterial and fungi population is stabilized and deceased in number.
5. The response of nematode population to mustard meal and compost application depends on soil and weather conditions. Both a decrease and an increase in number of total nematodes, fungal feeders and bacterial feeders may occur. Mustard meal treatment and basamid treatment decrease the number of spiral nematode in soil associated with damage to some crops.
6. Oil Radish treatment may present the best values for marketable yield and fruit dry weight in vegetable production. More experiments with compost treatments have to be conducted in order to check on the accumulative effect of compost and oil radish on vegetable production.
(1) Delvin’s Farm (Photo 5)
Location of the farm is 6290 McDaniel Road, College Grove, TN 37046. The owners of the farm are Hank Delvin and his wife Cindy Delvin. More details on the farm may be found at the website http://www.delvinfarms.com/contact.html. The objective of the experiment was on-farm testing of enhanced biofumigation and composting systems for organic production of tomato, eggplants and other vegetables. The experiment was conducted in 2004 and 2005.
Treatments of the experiment were the following:
1. Mustard (fall planting) +mustard meal + compost
2. Clover (fall planting) + compost
The treatments were replicated twice.
(2) Tannin’s Organic Farm (Photo 6)
Location of the farm is 8824 Dog Creek Road, TN. The owner of the farm is David Tannin.
The objective of the experiment was on-farm control of soil-borne pests of organic vegetables with enhanced biofumigation and composting systems. The experiment was conducted in 2004. The following treatments were applied with no replicates:
1. Mustard Meal, 20.6 lb per plot or 4000 lb/acre
2. Mustard Meal, 29.38 lb per plot or 4000 lb/acre
4. Mustard Meal, 29.38 lb per plot or 4000 lb/acre
(2) Brunswick Bio Trial (Photo 7)
This trial was at the Holden Brothers Farm, Brunswick, NC. The objective of the trial was to determine influence of compost materials on common vegetable cropping systems and to evaluate the biofumigative effect of oil-seed radish in vegetables production. The experiment was conducted in 2004 and 2005.The 2004 cooperator was Sam Bellamy at Indigo Farms Florist; 1542 Hickman’s Rd., Calabash, NC 28467. The 2005 trial is being conducted with Holden Brothers Produce, 5600 Ocean Hwy, W Shallotte, NC 28470. Test crops included squash and cantaloupe.
Treatments of the experiment were the following:
2. Oil Radish
3. Caliente Mix (Mustard)
4. Compost 15
5. Compost 30
6. Mustard Meal
7. Radish+Compost+Mustard Meal
The treatments were replicated three times.
More details on the trials are available at the website of the project http://web.utk.edu/~tkarpine/Experiments.html.
The main results obtained by on-farm testing are summarized below.
At this farm we tested not only the effect of enhanced biofumigation and composting on the yield of vegetables, but also bacterial and fungal activity in the soil. The bacterial activity (BA) of the soil was estimated as population densities of heterotrophic bacteria measured by CFU (Colony FormingUnits) per 1 g of dry soil (*10E-6). The fungal activity (FA) of the soil was estimated as population densities of fungi measured by CFU (Colony FormingUnits) per 1 g of dry soil (*10E-4).
The main results of the testing are presented in Tables 11 and 12. ANOVA analysis showed that there was no statistically significant difference between mean values of the fungal and bacterial activities in the pretreatment and postreatment soil samples at the farm (95.0% confidence level). Difference between the pretreatment and postreatment FA and BA values also didn’t show statistically significant difference. Nevertheless, BA values after treatments were higher by 119% at replicate 1 and by 22% at replicate 2 in 2004. The mean increase in BA value imposed by treatment with mustard meal and compost was 76% (Table 11, Figure 21). Though difference in the tomato yield were statistically not significant, the tomato yield at treated plots was by 36% higher at replicate 1 and by 20% at replicate 2 in 2004. Mean increase in the yield was 28% (Figure 21). Mean increase in the yield of tomato in 2005 was 14% (Table 12). The effect of treatment on the yield of eggplants was absent.
Brunswick Bio Trial
The main results of the trial are summarized in Table 13. There were differences among treatments in early and late harvest of marketable fruit. Oil Radish and RCM mix yielded the highest values in early harvest, Although the control treatment in early harvest presented a very lower value in pounds per acre, the yield marketable value in late harvest was the best. Compost 15 and Compost 30 were high in yield too. Total yield of marketable fruit showed no difference between treatments, however, final yield of the Control treatment was the highest, its came for late harvest. The best values in dry weight in both early and late harvest came from Control treatment followed by Compost 15 and Oil Radish treatments.
The microbial activity in the soil was not different between treatments, however Compost 30 shown the highest value before planting and after harvest. Significant differences were found between microbial activity before and after harvest. It was higher starting the season (10263 ppm vs. 7259 ppm of CO2)
Oil Radish treatment presented the best values for marketable yield and fruit dry weight among the treatments. More experiments with compost treatments have to be conducted in order to check on the accumulative effect of compost on production.