This research was designed to evaluate cover crop, soil amendment, and nitrogen rate on rice yield, milling quality, and disease severity in integrated studies conducted on organic land in Texas and South Carolina, USA. We have completed the field trials of this project to determine the impact of winter cover crops, soil amendments, and rice varieties on organic rice production at Beaumont, TX and Charleston, SC. In Texas, winter cover crops were established for each of the winters between 2012 and 2014. The amounts of dry biomass were 4,525 and 5,152 kg/ha for clover and ryegrass, respectively. The cover crop aboveground yields were comparable for 2013 and 2014 but lower for 2012. Due to poor rice stands, replanting was made in 2014 but in a field without the effect of winter cover crops. Rice variety had a significant effect on all tested aspects of rice production. Tesanai had higher grain yield and 1,000 grain weight than Presidio and XL753. The averaged grain yields over years for Tesanai, XL753, and Presidio were 9,949, 8,614, and 6,505 kg/ha, respectively. Compared to conventional cultivars, the hybrid XL753 had greater spikelets per panicle and filled grain per panicle than Tesanai and Presidio. Although there was a trend for increasing yield with nitrogen application, it was not statistically significant. However, application of soil amendments reduced the severities of narrow brown leaf spot and brown spot on the susceptible variety Presidio compared to the nonamended fertilizer control. Also, the severity of these diseases varied with rice cultivars with the hybrid having the lowest and Presidio having the highest in. No symptoms of straighthead were observed in plots with any treatments. Thus, as seen in previous years, although fertilizer amendments may have some positive impact on yield and disease control, these are not consistent nor likely economically cost effective. Choice of variety is much more important in optimizing yield and minimizing disease damage. Moreover, an economic analysis based on our field results and farmer-survey indicated that production costs are not as much an issue for organic rice as for conventional rice due to use of fewer costly inputs in organic production systems. Profitability does, however, hinge on obtaining a guaranteed monetary premium. In addition, having good control of irrigation resources for weed control is necessary for achieving profitability in organic rice production. In South Carolina, three-year field studies indicated that variety selection played important role in organic rice production. Winter cover crop selection was site specific. The results of this project have been delivered mainly through the field tours and workshops during the field days, through scientific meetings, on-farm demonstration, and published documents.
- Quantify the combined effects of cover crop, organic soil amendments, and variety selection on rice yield, milling quality, and disease severity with field trials conducted on organic land in conjunction with an established stakeholder research and outreach advisory board.
- Determine ecological services (carbon sequestration, nitrogen retention, and water quality) provided by organic rice farming using the proposed integrated practices.
- Demonstrate economic viability of integrated organic rice management through the use of enterprise budgets. Provide information to farmers, researchers, county agents, natural resource managers, and regional public officials on the production potential, financial viability, and ecological impacts of organic rice cropping systems.
The purpose of this project is to develop sustainable organic rice production practices in the Southern USA using cover crops, organic soil amendments and variety selection that will improve economic returns, reduce losses due to weeds and disease pressure, and will improve soil quality. Since 1995 organic rice acreage has increased almost 6 fold with over half of the 50,000 acres being grown in the southern US. The industry has expanded rapidly due to market demand. However, there has been little research conducted that is relevant to the unique flooded paddy system that is used to produce rice. On average, organic rice yields are 30-50% below conventional rice production in commercial fields (M. Doguet, pers. comm.). However, complete losses have been observed with improper nutrient or pest management. We conducted an informal survey of organic industry representatives from California, Arkansas, South Carolina, Texas, and Louisiana to identify researchable issues affecting organic rice production. The critical issues were nutrient management, weed control, and rice cultivars with high economic returns. Since then we have organized or participated in 7 organic rice workshops and have developed good partnerships with farmers, millers, end-users, and extension agents that are committed to development of practices that will support long term growth of the US organic rice industry. Although we have made progress on specific issues facing organic rice production, we propose a systems approach that uses cover crops, organic amendments, and variety selection.
Soil fertility is a key component to producing high yields that make organic farming systems economically viable. Essentially all rice in the USA is produced under flooded conditions as a means of controlling weeds and stabilizing yields. Nutrient availability is very different under anaerobic (flooded) conditions typical of rice production as compared to dryland or row cropping systems. In addition, rice is typically grown in heavy clay soils or those with a shallow hardpan in order to sustain field flooding. Thus, organic nutrient management methods that have been developed for other crops have limited use in rice and there have been few studies conducted in flooded-rice systems using organic based fertilizers. Golden et al. (2006), using preplant incorporated fresh and pelleted poultry litter, reported that rice grain yields increased linearly when 270 kg total-N ha-1 was applied to a direct-seeded, delayed-flood rice production system and approached the near maximal yields produced with urea-N. We have evaluated six organic fertilizer amendments using four rates in replicated yield trials conducted on organic land in Texas over two years (data now shown). All organic amendments significantly increased organic rice yield over the non-treated control except Organic Compost with Organic Alive Biological Tea. Compared to other organic fertilizer amendments, rice yields of Nature Safe and Rhizogen treatments had the best yield response to fertilizer application in 2010. In follow-up studies conducted in 2011, the highest yields were with 146 kg N ha-1 and 219 kg N ha-1 treatment for Nature Safe and Rhizogen, respectively.
Cover crops have been shown to enhance soil fertility, soil organic matter, and soil structure. Wander et al. (1994) reported that cover-cropped soil had higher total carbon (C) and nitrogen (N), and reduced water extractable organic C contents than conventional treatment soils. However, in anaerobic rice soils, where there is slow decomposition, the presence of phenolics in soil organic matter has been shown to reduce nutrient availability (Schmidt-Rohr, et al. 2004). Therefore, use of cover crops with high quality and biomass can increase soil N supply for organic rice production but nutrient availability is complicated by anaerobic/flooded fields. Identification of cover crops that can be successfully established and terminated in time for nutrients to be available at key time points of the rice growth cycle is critical for maximizing yields and reducing input costs for organic growers.
Stand establishment is a key issue for cover crops planted in clay soil as indicated by our preliminary studies and others (Lattimore et al. 1994). We have evaluated clovers, hairy vetch, winter wheat, cereal rye, cowpeas, sudangrass, soybeans, pearl millet, and ryegrass as summer/winter cover/green manure crops for organic rice production. For the proposed project, we will limit our research to the winter cover crops, white clover (also observed by Cho et al. 2003) and rye grass, that have demonstrated the best performance in stand establishment and biomass production in heavy clay soils. Determining the economic value (yield, input cost) and environmental impact (organic matter, water quality) of these cover crops is critical for the long term sustainability of organic rice production.
Growing rice cultivars that are N use efficient, disease resistant and can compete with weeds is important to organic rice production. Weisler et al. (2002) determined that N efficient cultivars had high N uptake during the reproductive stage. Gibson and Fisher (2001) found that seedling growth, leaf area, plant height, tillering, leaf angle, and root growth were factors that were beneficial for competing against weeds. In a two-year study comparing rice cultivars grown under organic management and two conventional management schemes (100% and 50% fertilizer inputs), McClung and Bergman (2002) found that organic management resulted in significant decreases in plant stand, plant height, maturity, and yield. Extended tillering, rapid canopy closure, and tall plant height are traits that would be beneficial under organic rice production but have been selected against in US commercial cultivars because of the negative impact of these respective traits on grain uniformity, disease susceptibility, and lodging susceptibility. Although most rice in the USA is produced for conventional long, medium, and short grain market classes, breeders have also developed cultivars having specific cooking quality properties for various high-value niche markets. These include varieties for use the in the flour or starch market, for parboiling, and those that have a popcorn-like aroma. Currently rice cultivars grown for the organic market include both conventional and specialty grain types. Thus, identifying rice cultivars that have high yield potential under organic systems and possess value-added grain properties will result in the greatest economic returns for farmers. In organic yield trials conducted in Texas in 2001-02 and 2009-10, we observed significant difference in yield potential of specialty and conventional varieties (data not shown).
Management options that can effectively control rice diseases are critical for organic production profitability and sustainability but remain largely unknown. We have observed that the fungal diseases narrow brown leaf spot (Cercospora janseana) and brown spot (Cochliobolus miyabeanus) and the physiological disorder, straighthead are among the most serious constraints affecting organic rice production in the southern US (Zhou and McClung, 2010, 2011) and are not commonly found under conventional management. Other diseases common to southern rice production, including sheath blight and blast (both fungal) and bacterial panicle blight, are looming threats. Hollier (1992) showed that narrow brown leaf spot and brown spot are more severe on rice plants grown in N-deficient soil. Our research indicates that straighthead can be more severe in organic rice production, especially including no-till and cover crops, compared to conventional production systems (Zhou and McClung, 2010). This demonstrates that systems which use organic fertilizers, no-till, and cover crops may increase susceptibility to diseases not common in conventional management making control of diseases a particular challenge in organic rice production. In addition, the timing of incorporation of the cover crop and planting the rice crop may be critical for controlling straighthead which causes complete sterility of the seedhead. Developing organic cropping systems which can effectively utilize cover crops and soil amendments to enhance soil nutrient quality but minimize disease losses is needed to maximize yield and economic returns.
Recent studies have demonstrated success utilizing various cover crops, including the legumes, for reducing a wide range of foliar and soilborne diseases in vegetables (Larkin and Honeycutt, 2006; Keinath et al. 2009; Mills et al., 2002; Snapp et al., 2005; Stone et al., 2004; Zhou and Everts, 2004, 2008). However, this new approach of using legume cover crops is underutilized in conventional and organic rice, where most rice is planted to fallow ground. This multidisciplinary project will take the lead to develop an effective cover crop-based disease management program in organic rice.
We also propose to use genetic resistance as one of the effective components to manage diseases. The results of our research conducted in Texas showed significant resistance existing in rice varieties against various diseases (Zhou et al., 2010b, 2011b). For example, Presidio, a leading organic variety, is susceptible to narrow brown leaf spot but is tolerant to straighthead. To further identify resistant varieties under different environments, we propose to establish a varietal trial in South Carolina that will evaluate both yield potential, economic value (conventional and specialty cultivars), and disease resistance. This will help to strengthen the emerging organic rice market in South Carolina.
Organic rice production may impact ecological services including C sequestration and water quality issues. Cover crops and soil amendments can influence soil carbon (C) sequestration and microbial biomass and activities by providing additional residue C to soil. Soils in the humid southeastern US have lower organic matter levels than in the temperate regions due to greater rates of mineralization and severe erosion as a result of a long history of intensive cultivation. In an extensive review of management practices effects in the southeastern US, Franzluebbers (2005) summarized that soil organic C sequestration with the application of poultry litter was 0.26 – 2.15 Mg ha-1 year-1 as compared with unmanured soil which was cropped more than 2 years. Application of soil amendments may cause water quality issues. The large accumulation of P in manure from animal feeding operations has increased the potential for P export following land application. Sharpley and Moyer (2000) reported that more than 80% of inorganic P was water extractable from manure. Such high soluble inorganic P may cause undesirable water issues in organic rice production. In an effort to develop agricultural best management practices for phosphorus reduction in south Florida, Izona et al. (1995) reported that a rice crop can be used to reduce phosphorus in drainage water. However, information is lacking regarding the effects of soil amendment application on water quality in organically produced rice.
Very little work has been done to evaluate the cost of organic rice management. Researchers in California have developed detailed production costs for water seeded and no-till organic rice in the Sacramento Valley (Williams et al., 1992 a, b). However, no recent costs have been documented for organic rice in the southern US. Organic rice production offers many management challenges that greatly impact the overall profitability of the enterprise. The enterprise budget is set up to help estimate what is expected if particular production practices are used to produce a specified amount of product. Development of enterprise budgets for organic rice production methods using the specific economic and technological relationships between inputs and outputs used in this study will serve to address the question of economic viability of organic rice production.
Organic cultural management practices have not been studied in detail in rice, thus this project aims to quantify the economic and ecological benefits of successful technologies and validate these in farmer fields. Consideration will not focus only on yield but also subsequent effects on grain quality, soil quality and soil health (beneficial microbial communities), water quality, disease suppression, and the overall economics of the whole production system. This information will identify the best production practices that are not only economical but also enhance ecological balance.
Throughout the implementation of this project, stakeholders have been, and will continue to be, involved as full collaborators and will participate in the design of experiments, treatments to be employed, data to be collected, interpretation of results, and ways to effectively transfer the technology to growers. The most successful combination of technologies will be validated in grower fields and will require their direct oversight and management. Such a collaborative arrangement will facilitate implementation and acceptance of research results by other growers.
One of the study sites was located on a certified organic land within the Texas A&M AgriLife Research Center of Beaumont (30o 3’ 54” N, -94o 17’ 45” W) in Jefferson County, Texas, approximately 15 km west of Beaumont. The soil was a loamy soil. The other site was located at the Clemson Coastal Research and Extension Center (CCREC) organic rice farm.
Winter Cover Crops
Two selected winter cover crops, Durana white clover and ryegrass, were planted on well-prepared seedbeds using a rig on November 1, 2011, October 12, 2012, and November 6, 2013. The seeding rates 16 kg/ha and 50 kg/ha were selected, respectively, for Durana white clover and ryegrass to achieve a better standing under wet winters. The winter cover crops were plowed down on April 14, 2012, March 7, 2013, and March 14, 2014, respectively.
The dry fall in 2012 delayed the germination of both cover crops. Both cover crops were terminated on March 7, 2013 and the fallow field areas of indigenous weeds, ryegrass, and some clover were cultivated.
After termination, the cover crops were left for two weeks to allow decomposing prior to incorporation. Our previous research has shown this is important to mitigate potential straighthead (a physiological disease) occurrence in the subsequent organic rice crop.
Winter cover crop treatments served as main plots with rice varieties (Tesanai – high yield, used for flour market, Presidio – superior long grain quality, and XL723 – high yield, new released hybrid that was suggested by the Organic Rice Production Advisory Board) as subplots. Both Tesanai and Presidio were planted in 2012, 2013, and 2014. XL723 was included in the 2013 trial and XL753 in the 2014 trial. Soil amendment treatments were applied as sub-sub-plots. Each treatment had four replications. Cover crops were managed as in the previous section. Soil amendments (Nature Safe vs. Rhizogen) with three levels (untreated control, 150 kg N/ha, and 210 kg N/ha) were applied and incorporated just after planting the rice in the plots approximately 5 m-2. Organic rice was drill seeded using a high seeding rate (160 kg/ha for Presidio and Tesanai, and 80 kg/ha for XL723 and XL753 which is double the recommended rate for hybrids). The planting dates were May 1, 2012, April 22, 2013, and April 21, 2014. Although both varieties emerged on the same date, compared to Presidio, Tesanai had longer growth duration and matured two or more weeks later. Plots were flush irrigated to encourage uniform germination and were maintained under a flood until harvest to help weed control. All plots were harvested by hand in 2012 as they came to maturity, in early August for Presidio and late August to early September for Tesanai. Plots planted in the fallow field had very poor stands due to severe weed pressure. Therefore, the only results of rice grain yields were from the clover and ryegrass treatments in 2012. In addition, we treated all the seed with OMRI certified gibberellic acid (GA) to promote seed germination in 2013 and 2014.
Organic rice was drill seeded on April 21, 2014 using a high seeding rate (160 kg/ha for Presidio and Tesanai, and 80 kg/ha for XL753 which is double the recommended rate for hybrids). Although the three varieties were successfully planted, the sudden drop in temperature severely impacted the emergence of rice seed which caused very poor stands; therefore, the trials were terminated. We replanted the organic rice trial at a different part of the organic field but which had not been planted with cover crops in the previous fall. Thus, in the new plots (trials) we only tested the effect of cultivar and nitrogen rate on organic rice production.
The effects of rice cultivar, cover crop and soil amendment on severity of narrow brown leaf spot (NBLS), brown spot, and straighthead were also investigated in the same field trials as for organic rice production at Beaumont during 2012-2014 rice seasons.
In addition, two greenhouse assays were conducted to evaluate if cover crop-amended soils can induce systemic resistance against NBLS and enhance the growth of rice plants.
Effects of field plot soils incorporated with cover crops: Soil samples were randomly collected prior to planting of the 2013 rice crop and after the winter cover crops had been terminated in the fallow, clover, and ryegrass fields. Presidio was seeded into 5.1-cm pots filled with the soil samples in the greenhouse. At 4 weeks after seeding, rice seedlings were inoculated with the conidia of the NBLS fungus and disease severity was rated at 4 weeks after inoculation. Plant height and dry above ground biomass were measured 4 weeks after seeding and at maturity, respectively.
Effects of cover crop amendment rate: Ground powder of clover and ryegrass was incorporated at 0, 0.2, 0.8, and 3.2 % (wt/wt, approximately equivalent to 0, 2, 8, and 32 tons of fresh above ground biomass per acre) into soil collected from a field that had been in fallow-rice organic management for many years. Presidio was seeded into the treated soils and the NBLS pathogen was inoculated as described above. Disease severity and plant growth parameters (plant height and dry above ground biomass) were measured as described before.
Charleston, South Carolina
Over the last 20 years there has been increasing interest in re-establishing rice production in South Carolina for the primary purpose of supporting the local food market. Currently there are some 600-700 acres of conventional rice production with an additional ~150 acres in organic rice. However there is essentially no local research to support these operations, thus this research was undertaken to test findings from the Texas environment in South Carolina. The field at the CCREC had been planted to Dixie Crimson Clover in fall 2011. In April 2012 the cover crops was terminated and disked three times prior to the levees being pulled in mid-April. Fertilizer consisted of Nature Safe 13-0-0 broadcast at 1,000 lbs /Ac and worked into the soil profile with a Perfecta II field cultivator. Field plots for each of 6 varieties were laid out as unreplicated strips approximately 9.75 m2. Each plot was encompassed by metal flashing and the field was flooded. Seed from each variety was presoaked and allowed to pip (germinate) prior to hand seeding into the flooded strip plot on May 7. The field was drained and the pre-germinated seed was allowed to peg into the wet soil prior to re-flooding. During the season days to heading, plant height, and days to harvest were recorded. At harvest a 0.93 m2 area was hand harvested in three areas within each strip. Samples were air dried in a greenhouse then grain moisture and grain yield were determined. Rough rice samples were sent to Arkansas where 125 g samples from each replicate were used for milling determination using a McGill No. 2 miller.
The field at the CCREC-ORF (organic rice field) that had been under organic management for a number of years was planted with certified organic annual rye grass (Lolium multiflorum) at 168 kg/ha in the fall 2012. One month before rice seeding on April 1st, 2013, the annual rye grass was mowed and tilled into the soil to prevent allelopathic effects on the rice germination. Soil samples were taken on April 14th, 2013. Fertilizer consisted of Nature Safe 8-5-5 broadcast at 179 Units N/ha and tilled into the soil profile. The study included six varieties; Tesanai, Presidio, and XL723, common to the TX study, and Carolina Gold, Charleston Gold, and IAC 600 of particular interest for organic production in SC. The study was laid out in a completely random design with four replications. Seed from each variety was pre-soaked and allowed to pip (germinate) prior to hand seeding into the flooded field on May 9. Each plot was surrounded by metal flashing to prevent movement of the seed and soil amendment into adjacent plots. The field was drained and the pre-germinated seed was allowed to peg into the wet soil prior to re-flooding. During the season, days to heading, plant height, and days to harvest were recorded. Unlike the prior year in 2012, in 2013 we applied Serenade Max (Bacillus subtilis. strain QST 713) for disease control. At harvest a 0.93 m2 area was hand harvested within each replication and subjectively graded for disease and physiological disorders.
Fall of 2013, a certified organic field located at the CCREC, with organic matter of approximately 7% was disked twice, leveled and seeded with ‘White Dutch Clover’ (Trifolium repens) at 12 lbs/Ac (13.4 kg/ha). In the spring 2014, the field was flail mowed and disked multiple times. Based on soil test results, Nature Safe 8-5-5 fertilizer was broadcast at 160 Units N/Ac, tilled into the soil profile and then flooded. On May 9, 2014 pregerminated seed of six rice cultivars: Carolina Gold, Charleston Gold, Presidio, Tesanai II, IAC 600, and XL 753 were broadcast in plots 9.3 m2. A completely randomized block design with four replications was used. After the rice was pegged, the field was re-flooded. However the study was completely lost due to weeds and had to be replanted in the same manner on June 6, 2014. Serenade Max (Bacillus subtilis. strain QST 713) was applied every 1 or 2 weeks throughout the season for disease control. Days to flowering, heading and height data were collected prior to harvest. At harvest, 0.03 m2 area plot subsamples were hand harvested and graded for narrow brown leaf spot, brown leaf spot, bacterial panicle blight and straight head. The graded bundles were then hung in a drying greenhouse for approximately 36hrs until rice kernels achieved 12% moisture and then the bundles were threshed with a Kincade plot combine and then weighed. Plot yields were then shipped to USDA Agricultural Research Service, Dale Bumpers National Rice Research Center, to determine milling quality.
Floodwater samples were periodically collected from each plot using a clean plastic centrifuge tube during the rice production. Once collected, the water samples were kept in a cooler and immediately stored in a freezer until analysis. During water sample analysis, tubes were transferred into a refrigerator for melting. Water samples were first filtered using a DF/F glass filter paper and then measured for organic carbon and nitrogen and pH and EC values.
Soil samples were collected after rice harvesting and air dry until constant weight. The air dried soil samples were finely ground to pass a 0.5 mm screen for organic carbon and total nitrogen analysis using wet chemistry. Rice grain samples were collected from each plot after milling and finely ground for total nitrogen analysis using wet chemistry.
Efforts were made in 2014 and 2015 to contact organic rice producers and sellers in both Texas and Arkansas to determine the ways organic rice is grown, identify factors affecting organic rice profitability, and calculate organic rice production budgets in both states. Much information was gleaned from this effort, which first began in Texas. In 2014, production costs for organic rice were estimated for key counties producing organic rice in Texas and were compared with those for conventional rice. Some general conclusions were gleaned from conversations with Texas and Arkansas organic rice producers and sellers.
Winter Cover Crops
The dry aboveground biomass yields of clover were 4,690, 4,837, 4,525 kg/ha for 2012, 2013, and 2014, respectively. The dry aboveground biomass yields of ryegrass were 5,157, 5,907, 5,152 kg/ha for 2012, 2013, and 2014, respectively. Compared with the season of 2012, the yield of clover during 2013 was lower, likely due to low soil moisture during seed germination. The total nitrogen contents of the dry biomass were 2.0 and 1.2% for clover and ryegrass, respectively.
Although numerically, rice grain yield following the ryegrass cover was higher than that under clover treatment, the difference was not significant. Rice varieties were different for grain yield with Tesanai having significantly higher grain yield than Presidio. The grain yield of Tesanai was 75% higher than that of Presidio. Similar to cover crops, soil amendments did not have significant effect on rice grain yield. The grain yield using Nature Safe was similar to that with Rhizogen, indicating that both were equally effective in providing nutrients for organic rice production. However, the application rate of soil amendments significantly affected rice grain yield. Compared to the control (0 applied), both the 150 kg N/ha and 210 kg N/ha soil amendment application rate increased rice grain yields by 11%. There was no difference in rice grain yields between the two N rates, indicating that 150 lb N/acre was sufficient for organic rice production in terms of N supply. Both cover crop and variety did not affect rice seedling establishment. Compared to Presidio, Tesanai had higher plant height. The weed density under Presidio was greater than that under Tesanai, indicating that greater weed competition with Presidio. Aboveground biomass of the rice crop was affected by the rate of soil amendments rather than the type of soil amendments. Compared to the control, application of soil amendments significantly increased aboveground biomass. Also, the aboveground biomass was highly correlated with the corresponding grain yield. Rice milling yield was significantly affected by cover crop and rice variety. Higher milling quality (whole grain yield) was observed with the ryegrass treatment than with clover. Also, Presidio had higher milling quality than Tesanai.
The winter cover crops when averaged over all soil amendment treatments did not significantly affect the main crop (MC) grain yields in 2013 (Fig. 1). The average MC grain yields were 7,443, 7,292, and 7,312 kg/ha for clover, ryegrass, and fallow treatments, respectively. Our two-year studies indicated that ryegrass and clover had the same effect on organic rice production in southern USA.
Rice variety had a significant effect on MC grain yield. Tesanai had higher MC yield than XL 723 and Presidio (Fig. 2). Grain yield using Nature Safe was similar to that with Rhizogen, indicating that both were equally effective in providing nutrients for organic rice production. However, the application rate of soil amendments significantly affected rice grain yield. Compared to the control (0 applied), both the 150 kg N/ha and 210 kg N/ha soil amendment application rate increased rice grain yields by 6%. There was no difference in rice grain yields between the two N rates, indicating that 150 kg N/ha was sufficient for organic rice production in terms of N supply. Plant height decreased in the order of Tesanai, XL723, and Presidio. Although taller varieties would be expected to have an advantage in weed competition, the weed density was very low in 2013 organic rice trials.
Rice milling yield of MC was significantly affected by cover crop and rice variety. Higher milling quality (whole grain yield) was observed with the ryegrass treatment than with clover and fallow. Also, the highest milling yield was with Presidio and lowest with Tesanai.
To our knowledge, no study has been reported on the potential of ratooning in an organic rice system. In 2013, we tested rice ratoon potential (harvest of a second crop following regrowth from the crop’s stubble) and our preliminary results indicated that organic rice ratooning was promising if the crops were planted in a timely manner.
Rice variety had a significant effect on all tested aspects of rice production (Table 1). Tesanai had higher grain yield and 1,000 grain weight than Presidio and XL753 (Table 2). The averaged grain yields for Tesanai, XL753, and Presidio were 9,949, 8,614, and 6,505 kg/ha, respectively. Compared to conventional cultivars, the hybrid, XL753, had greater spikelets per panicle and fertility per panicle than Tesanai and Presidio. Presidio had higher milling yield and percentage of filled grain on the panicle than the other cultivars and was not significantly different from XL753 for harvest index (Table 2).
There were no significant differences among the nitrogen applications (Table 1) although there was a trend for increased rice grain yield, milling quality, percentage of filled grain, and harvest index with the split application of nitrogen as compared to the control (Table 3).
The effects of rice cultivar, cover crop and soil amendment on severity of NBLS, brown spot, and straighthead were also investigated in the same field trial as for organic rice production at Beaumont in 2012. Severity of NBLS was significantly higher (P<0.05) on Presidio than on Tesanai while severity of brown spot was similarly low for both cultivars. These results indicate that Presidio was very susceptible to NBLS and Tesanai was resistant in this organic rice production system, which is in agreement with our previous studies. Cover crop treatments did not affect NBLS. However, the clover cover crop treatment had a significantly lower brown spot severity compared to the winter fallow and ryegrass treatments. Neither fertilizer, NatureSafe or Rhizogen, affected the severity of NBLS or brown spot symptoms. Application of N at either 150 or 210 lbs/acre was effective in reducing severity of NBLS and brown spot as compared to the control. Severity of either disease linearly (R2=0.56) decreased with the increased N rate applied. In addition, no symptoms of straighthead were observed in any plots.
Cover crop treatments in 2013 significantly affected the severity of NBLS and brown spot on Presidio (Fig. 3) but not on the more resistant Tesanai (Fig. 4) and XL723 (Fig. 5). The severity of NBLS and brown spot was lowest in the clover cover crop treatment and highest in the fallow treatment (Fig. 3). Severity of NBLS was significantly lower (P ≤ 0.05) on Tesanai and XL723 than on Presidio. Both Presidio and XL723 had a similar but higher levels of brown spot compared to Tesanai. The fertilizers, NatureSafe and Rhizogen, did not affect severity of both NBLS and brown spot. Application of N at either 150 or 210 kg/ha did not significantly affect severity of NBLS and brown spot either. No symptoms of straighthead were observed in plots with any cover crop treatments including fallow. The results of this field study indicate that use of resistant cultivars such as Tesanai and XL723 and clover cover crop was effective in reducing NBLS and brown spot. When growing a more susceptible cultivar like Presidio, a cover crop was effective in reducing the level of disease as compared to the fallow treatment.
In 2014, application of Rhizogen at either 90+60 (N two-way split) or 150 kg N/ha (one time at planting) equally reduced the severities of NBLS and brown spot on Presidio compared to the nonamended fertilizer control (Table 4). Application of the fertilizer at either 90+60 or 150 kg N/ha also reduced brown spot severity on XL753. Severity of NBLS was highest (3.5 on a scale of 0 to 9) on Presidio, least (0.8) on XL753, and in intermediate (2.0) on Tesanai. Tesanai (1.5) has a significantly lower severity of brown spot than Presidio (3.0) and XL753 (2.7). No symptoms of straighthead were observed in plots with any treatments. The results of this field study indicate that resistant cultivars such as Tesanai and XL753, optimum fertilizer N level and cover crop can be effective tools to reduce the damage caused by diseases in organic rice.
Two greenhouse assays were conducted to evaluate if cover crop-amended soils could induce systemic resistance against NBLS and enhance the growth of rice plants. Clover and ryegrass amendment treatments did not reduce the severity of NBLS compared to fallow control treatment (Table 1). Both cover crop treatments did not improve plant height either. However, both cover crop treatments significantly increased dry above ground plant biomass with clover cover crop treatment being more effective than ryegrass cover crop treatment. Unlike the field trials, the results of this greenhouse assay indicate that field soils incorporated with clover or ryegrass cover crop did not induce resistance to NBLS but enhanced plant growth.
Our second greenhouse trial indicated that all the amendment rates of clover and ryegrass did not reduce the severity of NBLS compared to the untreated control (Table 2). However, either clover or ryegrass at 3.2% significantly increased plant height and dry above ground biomass compared to the untreated control. The results of this amendment rate study are in agreement with the results of the field plot soil amendment study conducted in the greenhouse, indicating that soil amendment with a high rate of clover or ryegrass could improve rice plant growth but did not induce resistance against the NBLS disease. The differences in disease control between the field and greenhouse study could be a result of other factors impacting the spread of the disease in the field versus the greenhouse where all plants were artificially inoculated.
In the 2014 rice season (April-August), impacts of winter cover crop (ryegrass vs. fallow), nitrogen rate (0, 150 kg N/ha with split, and 150 kg N/ha single application), and cropping system (organic vs. conventional rice system) on water quality [electronic conductivity (EC), pH, dissolved organic carbon (DOC) and dissolved total nitrogen (DTN), and water soluble inorganic phosphorus (P)] were evaluated. Cropping system and N rate had little effect on EC, pH, DOC, DTN, and P of the floodwater during rice season. However, the rice growth stage had slightly effect on the EC of the floodwater with a general decreasing pattern with rice growth. The floodwater pH values were affected by both cropping system and rice growth stage. Under organic fallow system, the pH value slightly increased and then decreased with rice development. However, under conventional rice system, the pH value slightly decreased with rice growth. For DOC and DTN of the floodwater, there were no consistent patterns observed cross the treatments. The water soluble P was quite constant during rice growth for all treatments. Our 2014 results indicated that there were no significant differences in water quality between organic and conventional rice systems and the winter cover crop and N rate had minimal effects on water quality.
Charleston, South Carolina
Prior to harvest in 2012, evidence of sheath rot (Sarocladium oryzae) and brown spot diseases and rice water weevil (Lissorhoptrus oryzophilus Kuschel) symptoms were noted. Brown spot and sheath rot were most prevalent in the Charleston Gold and the IAC 600 whereas straighthead was more of a problem in the Carolina Gold and Charleston Gold. Some brown spot was also observed in the STG 06L-35-061 and Presidio but not as severe. The highest yielding cultivars were Tesanai and Presidio. The variety STG 06L-35-061 is a new germplasm release derived from allelopathic cultivars PI31277 and PI338046. The other three varieties are for specialty markets: IAC600 -purple aromatic, Charleston Gold -long grain aromatic, and Carolina Gold – heirloom variety; the latter two are currently being grown commercially in South Carolina. These results indicate that there is significant room for improvement in yield potential, maturity, and height based upon choice of cultivars for production in South Carolina. However, varieties must also have grain quality traits suitable for local markets. Milling yield was extremely low for all varieties and was attributed to overdrying the samples in the greenhouse. The 2012 South Carolina results were also compared with two years of data from Texas. Although STG 06L-35-061 had not been grown in Texas before, two of its parents, PI31277 and PI338046, had been and were averaged for general comparison. Although the magnitude was different between yields of the varieties at the two locations, the ranking was very similar.
As in TX in 2013, Tesanai had significantly higher yield than other cultivars (4426 kg/ha), followed by Presidio and XL723 which were not significantly different. Although these varieties are suited to high value niche markets, Charleston Gold, Carolina Gold, and IAC 600 were the lowest yielding in the trial. Weed and disease pressure were not high, however more weeds were observed in the shorter varieties Presidio and IAC 600.
Field yields per acre in 2014 were as follows; 1) Carolina Gold = 2,809, 2) Charleston Gold = 7,434, 3) Presidio = 6,913, 4) Tesanai = 11,399, 5) IAC 600 = 3,927, and 6) XL753 = 10,842. Tesanai and XL753 had significantly higher yields than the other four cultivars. Charleston Gold and Presidio had similar yields and were significantly greater than IAC 600 and Carolina Gold which were not significantly different from one another. All but IAC 600 (purple bran variety) were milled to determine whole milling yields. The chart demonstrates crop value (whole grain rice x yield per acre) using head rice yields, except for IAC 600 which is presented as brown (hulled) rice yield (Fig. 1). These results demonstrate wide differences in economic yields among the varieties.
Of the three years the study was conducted, yields were greater in 2014 than the other two. There were no significant differences for disease pressure and physiological disorders (i.e. straighthead) with ranking of severity generally not exceeding 0.75 on a 0-5 scale. Although weed pressure early caused an initial crop failure in 2014 resulting in replanting, the weeds that were present in the final stands did not result in a noticeable loss in yields. Based on the past three years of data, recommendations are now being made to growers in South Carolina and there has been a rise in conventional rice production as well as transitional and organic rice acreage. Further work is needed for cultivar trials to further this progress in South Carolina.
Educational & Outreach Activities
- Dou, F., A. McClung, and X. G.. Zhou. 2013. The impacts of soil amendments on organic rice production (oral presentation). Annual Meeting of the Soil Science Society of America. Tampa, FL. November 2013.
- Dou, F., A. McClung, and X. G. Zhou. 2013. Integrating choice of variety, soil amendments and cover crops to optimize organic rice production. Texas Rice Special Section.
- Dou, F. 2013. Improving soil quality to increase yield and reduce diseases in organic rice production (oral presentation). 2013 Organic Rice Workshop, Houston, TX.
- Dou, F. 2013. Improving soil quality to increase yield in organic rice production (poster). Field Day. Eagle Lake, TX.
- Dou, F. 2013. Improving soil quality to increase yield in organic rice production (poster). Field Day. Beaumont, TX.
- Dou, F., X. G. Zhou, A. McClung, J. Storlien, Y. Lang, A. Torbert, F. Hons, B. Ward, S. Kresovich, and J. Wight. 2014. Cover crop, soil amendments, and variety effects on organic rice production in Texas (oral presentation). 35rd Rice Technical Working Group Meeting. New Orleans, LA. February, 2014.
- Zhou, X. G., Dou, and A. M. McClung. 2013. Effects of cover crops, fertility, cultivars, and biocontrol agents on organic rice diseases. Organic Rice Advisory Meeting. Mar. 20. 2013. Houston, Texas, USA.
- Zhou, X. G. 2013. Organic rice disease management. Pages 56-59. 2014 Texas Rice Production Guidelines. Texas AgriLife Research and Texas AgriLife Extension. B-6131. https://beaumont. tamu. edu/eLibrary/Bulletins/2014_Rice_Production_Guidelines. pdf.
- Garrett, T.F. and F. Dou. 2013. SARE. Learning experience of organic rice production. 2013 Southern SARE Young Scholar Enhancement Program.
- McClung, A.M., Duke, S., and Chaney, R.L. Impact of Organic Production Management on Variety Yield and Grain Arsenic Accumulation. 35rd Rice Technical Working Group Meeting. New Orleans, LA. February, 2014.
- Dou, F., X. G. Zhou, A. M. McClung, J. Storlien, Y. Lang, A. Torbert, F. Hons, B. Ward, S. Kresovich, and J. Wight. 2014. Cover crop, soil amendments, and variety effects on organic rice production in Texas. 35rd Rice Technical Working Group Meeting. New Orleans, Louisiana, USA. Feb. 18-21, 2014. P. 119-120.
- Dou, F. 2014. Summary of 2013 organic rice production. Presentation made at the Organic Rice Workshop of the 67th Annual Beaumont Field Day. Beaumont, TX, July 10, 2014.
- Watkins, K.B. 2014. Economics of organic rice production. Presentation made at the Organic Rice Workshop of the 67th Annual Beaumont Field Day. Beaumont, TX, July 10, 2014.
- Zhou, X. G. 2014. Effects of cover crops, fertility, and cultivars on organic rice diseases. Presentation made at the Organic Rice Workshop of the 67th Annual Beaumont Field Day. Beaumont, TX, July 10, 2014.
- McClung, A.M. 2014. Impact of variety and organic production methods on yield, quality, and grain arsenic. Presentation made at the Organic Rice Workshop of the 67th Annual Beaumont Field Day. Beaumont, TX, July 10, 2014.
- Watkins, K.B. 2014. Economics of organic rice production. Presentation made at the Organic Rice Workshop of the 67th Annual Beaumont Field Day. Beaumont, TX, July 10, 2014.
- Ward, B. 2014. System of Rice Intensification Cultivar Trials 2014. Presentation made at the Organic Rice Workshop of the 67th Annual Beaumont Field Day. Beaumont, TX, July 10, 2014.
- Dou, F., G. Zhou, F. Hons, A.M. McClung, S. Wang, Y. Lang, G. Li, J. Storlien, J. Wight, K. Landry, and G. Liu. Improving organic rice production through combining cover crop, soil amendment, and variety selection. The 67th Annual Beaumont Field Day. Beaumont, TX July 10, 2014.
- Tarpley, William and Fugen Dou. Internship with Organic Rice Production. 2014.
- Dou, F., F. Hons, X. G. Zhou, A. McClung, S. Wang, A. Torbert, Y. Lang, G. Li, J. Storlien, and J. Wight. 2014. Effects of cover crop and soil amendment on organic rice production. Annual Meeting of the Soil Science Society of America. Long Beach, CA. November 2014.
- McClung, A.M., Gerads, R., Chaney, R.L., Dou, F., Zhou, X. G., Duke, S.E. November 2-5, 2014. Organic rice production: minimizing exposure to grain arsenic. ASA-CSSA-SSSA Annual Meeting Abstracts, Long Beach, CA. 61-4.
- Storlien, J., F. Dou, G. Liu, and F. Hons. 2014. Organic rice management effects on greenhouse gas emissions in southeast Texas. Annual Meeting of the Soil Science Society of America. Long Beach, CA. November 2014.
- Chen, Ming-Hsuan and McClung, Anna. 2015. Effects of cultivars, organic cropping management, and environment on anti-oxidants in whole grain rice. Cereal Chemistry (accepted March 17, 2015).
- Watkins, K.B. and R. Mane. 2015. Organic Rice Production in Arkansas. Presentation made at the Organic Rice Workshop of the 68th Annual Beaumont Field Day. Beaumont, TX, July 9, 2015.
- Tan, Tommy and Fugen Dou. Internship with Organic Rice Production. 2015.
The results from the six year-site trials have been delivered to stakeholders including county extension agents, producers, scientific community, visiting scientists, postdoc research associates, technician, student workers, and industry consultants through field day tours, workshops, seminars, presentations, published materials, scientific meetings, and on-farm demonstrations. The results and outcomes of the research project will be published in scientific papers.
We have organized three field tours and four workshops during the annual field days in the Beaumont Center. Cumulatively, more than 100 audiences of producers, industry consultants, county extension agents, and students attended our tours and workshops.
This project has trained three visiting scientists, two postdoctoral research associates and one graduate student. Also, this project along with the SARE Young Scholar Programs has trained three students (two high school students and one undergraduate). The presentations produced by the students were submitted to the S-SARE office.
In addition, an Advisory Committee including was assembled in late 2012. Annually, we had a workshop to update our progress in organic rice research and suggestions and comments from the Advisory Committee were used to improve our research efforts. For example, we added hybrid varieties in our field trials which were suggested by our Advisory Committee to reflect the increasing interest of producers on this entry. Additionally, in 2014, an on-farm demonstration trial was conducted on the field of one of local organic rice producers, Salci Slack.
The results from this project have been presented at five national or international scientific meetings through oral or poster presentations including Rice Technical Working Group (RTWG) and ASA-CSSA-SSSA annual meetings.
Efforts were made in 2014 and 2015 to contact organic rice producers and sellers in both Texas and Arkansas to determine the ways organic rice is grown, identify factors affecting organic rice profitability, and calculate organic rice production budgets in both states. Much information was gleaned from this effort, which first began in Texas. In 2014, production costs for organic rice were estimated for key counties producing organic rice in Texas and were compared with those for conventional rice. These budget results were presented to participants of an organic rice workshop held July 10, 2014 at the Beaumont, Texas Field Day. The presentation was entitled “Economics of Organic Rice Production.” In 2015, organic rice producers in Arkansas were contacted to determine the practices in existence for organic rice production in this state. The information gleaned from these conversations was presented at a second organic rice workshop held July 9, 2015 at the Beaumont, Texas Field Day. This presentation was entitled “Organic Rice Production in Arkansas.” Results from both states will be presented during an organic rice symposium at the 36th Rice Technical Working Group Meeting to be held in Galveston, Texas during March 1 – 4, 2016.
Some general conclusions were gleaned from conversations with Texas and Arkansas organic rice producers and sellers. One of the primary challenges of organic rice production is growing a rice crop without using inorganic inputs that are commonplace in conventional rice (inorganic herbicides, insecticides, fungicides and fertilizers). The absence of such inputs makes cultivar selection and good water management very important in an organic rice system. The primary fertility inputs currently used in organic rice production are chicken litter and/or cover crops. Varieties with good weed or disease suppressive traits are more ideal than varieties susceptible to pests. Water is the one input that is most indispensable in organic rice production. Flood is the most effective means of controlling weeds, and good flood management can also reduce damage from diseases. Good flood control requires a consistent source of water and good control moving water across the field. The latter usually means precision leveling is needed. Organic rice fields are usually precision leveled and are generally no more than 16.2 ha (40 ac) in size to allow for good water control across the field. Organic rice levees are typically taller than conventional levees to allow for good control of grass weeds. Approximately one-third more water is applied to organic rice than to conventional rice.
Production expenses are not as big an issue with organic rice as with conventional rice. This is due ironically to the absence of inorganic production inputs in the organic rice system. The main component necessary for profitable organic rice production is a guaranteed price premium, as organic yields are typically much lower than conventional yields. The organic rice producer must have a buyer or buyers already at hand in order to receive a price premium. The crop is typically sold by contract, and the buyer often dictates the type of rice cultivars to be grown. The price obtained for organic rice is generally twice that for conventional rice. A few barriers to entry were also mentioned by organic rice growers. One barrier is the three-year waiting period required for organic certification of rice ground. There is no established market for rice grown in this transitionary period and the producer must wait three years to obtain the organic rice premium. Another barrier to entry is the inability to obtain operating loans for organic rice. Organic rice also requires large amounts of paperwork for yearly inspection and certification. It is also hard for to grow both conventional and organic rice. It is best to segregate equipment for both rice products. Finally, organic rice must be grown in rotation either with other organic crops or with fallow ground. A four-year rotation is typical for organic rice.
The primary information obtained from organic growers and sellers will be used to develop organic rice production budgets. Partial budget analysis will be conducted to identify profitable and cost effective organic management practices and to evaluate the profitability of research results from this and future organic rice research projects. Plans are also underway to continue direct interaction with organic producers to obtain more information about organic rice management and to create interactive organic rice budgets to assist producers in profitability estimation.
At least 250 farmers have been reached by this research project so far through field days tours, workshops, training sessions, and scientific meetings which farmers regularly attend. More farmers will be reached by the research project through the continuing field day tours and workshops and presentations and videos that will be readily available on-line in the near future. There has been a lot of interest by farmers of conventional rice production. Farmers are becoming increasing aware of the benefits of using cover crops and soil amendment addition production practices. We expect significant adoption of organic rice production over time. Variety selection was successful during this project, and thus this production system would be a good starting place for farmers considering organic rice production.
Areas needing additional study
More research needs to be conducted on sustainable nutrient (nitrogen) management in organic rice production. Low tillering and possible nutrient stresses during organic rice production create big challenges to organic rice production. Also, optimal planting time should be studied too. Research is needed to breed cultivars specific for organic rice production which can sustain low nitrogen supply and resist to disease and weed stresses.