The Transition from Conventional to Low-Input or Organic Farming Systems: Soil Biology, Soil Chemistry, Soil Physics, Energy Utilization, Economics, and Risk

Final Report for SW99-008

Project Type: Research and Education
Funds awarded in 1999: $153,962.00
Projected End Date: 12/31/2003
Region: Western
State: California
Principal Investigator:
Steven Temple
University of California
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Project Information


A 12-year comparison of organic, low-input, and conventional farming systems showed that yields were similar among all systems, with differences between systems less than those between years. The organic system with premium prices was the most profitable. Soil organic carbon was doubled in 10 years in the organic system. Runoff from cover-cropped systems was 1/3 that from conventional systems. The conventional farming systems were least efficient at storing excess N. Arthropods, pathogens, and nematodes had little influence on crop yields. Weeds resulted in small but detectable yield losses, and higher production costs in some years in the organic systems.

Project Objectives:

1. Over a twelve-year period encompassing three, four-year rotation cycles, compare four farming systems with different levels of reliance on non-renewable resources with regard to:
a.Crop growth, yield, and quality as influenced by different pest management, agronomic and rotational schemes of the four farming systems.
b. Abundance and diversity of weed, pathogen, arthropod, and nematode populations and their impact on crop growth, yield, and quality.
c. Changes in soil biology, physics, chemistry, and water relations and their impact on soil quality and productivity.
d. Cost of production inputs, value of production, economic risk, energy budgets for agricultural production under the four farming systems.
2. Compare and evaluate novel low-input and organic farming tactics, with emphasis on innovations that correct deficiencies, enhance profitability or decrease risk in each farming system.
3. Distribute and facilitate adoption of information generated by this project to all interested parties as it becomes available.


Environmental, economic, and social concerns related to commercial agriculture have become both heightened and focused in the past decade. Respirable dust in the form of PM-10 has been recognized as a serious air quality concern (Pope et al., 1992; Abbey et al., 1995; USEPA 2000), with much of the PM-10 arising from agricultural operations (Clausnitzer and Singer, 1997; Grantz et al., 1998; CARB, 1999; USEPA, 2000). Water penetration problems continue to increase in severity in most irrigated farmlands in the arid and semi-arid West, increasing flood risk and decreasing yields. Agriculture has been shown to be a major contributor to carbon emissions (Post et al., 1990; Lal et al., 1998). Agriculture is the biggest consumer of scarce Western water and the main source of polluted runoff to California’s rivers and streams (SWRCB, 1996).

Yet agriculture also provides essential public amenities, such food, fiber, wildlife habitat, open space, and floodwater retention. It is becoming increasingly difficult for farmers to succeed in the U.S.: prices received by farmers have decreased by 8 per cent in the last decade while prices for farm inputs have increased by 21 per cent. Fuel, machinery and labor costs have increased at an even greater rate than overall, with fuel prices more than 50 per cent higher than they were in 1990 and machinery and labor posting over a one third increase (NASS, 2000). In order to remain profitable, farmers have had to continuously adopt new technologies that increase production efficiency, increase yield per acre or both. They are on a treadmill, constantly trying to stay ahead of rising costs by changing production practices to either cut costs or increase yields. Simultaneously, they are attempting to avoid negative environmental impacts from farming, either because of personal convictions, regulations, or both. The result of these combined problems is that even the best growers are leaving agriculture and high-quality farmland is rapidly being converted to urban uses, with consequent losses in open space, wildlife habitat, and biodiversity (Medvitz, 1999; Blank, 2000; Sanders, 2000).

Alternative approaches to agriculture, including organic and low-input practices, have emerged in response to concerns over environmental degradation, natural resource consumption, human health risks, and rural economic decline associated with industrial agriculture. Alternative agricultural systems are typically based on a blend of traditional practices and ecological principles which allow for the reduction or elimination of synthetic chemical inputs. While the kinds of alternative systems range widely from those based on modern scientific knowledge to those integrating elements of spirituality, the underlying strategy is to manage the agroecosystem in such a way that it more closely resembles unmanaged ecosystems in both structure and function (e.g. tighter nutrient cycling and greater biodiversity). At the same time, productivity for human purposes must be maintained. Thus, research on alternative cropping and farming systems must consider both the goals of long-term sustainability and short-term productivity and profitability.

Ecological comparisons of conventional and alternative agricultural systems have demonstrated fundamental differences in variety of biological, chemical, and physical factors which may directly or indirectly affect crop growth and yield (e.g. Reganold et al. 1993, Drinkwater et al. 1995). Consequently, studies evaluating the effects of alternative farming systems on crop yields by simply reducing or eliminating industrial inputs in otherwise conventionally-managed systems do not accurately represent conditions occurring in alternatively-managed agroecosystems. Complex interactions and feedback among soil, crops, pests, and inputs necessitate empirical systems analysis. Studies in Maryland (Abdul-Baki et al. 1996), Pennsylvania (Steffen et al. 1995), South Dakota (Smolik et al. 1993; 1995), California (Drinkwater et al. 1995), and New Zealand (Reganold et al. 1993), for example, have shown that alternative systems can perform as well agronomically as conventional systems. However, other studies indicate that the use of low-input and organic production methods can lead to unpredictable, and sometimes substantial, reductions in crop yield and profit (Liebhardt et al. 1989, Sellen et al. 1995, Nelson & King 1996).

Research results generated from the SAFS project have filled a void and provided important information on the agronomic, economic, and ecological viability of low-input and organic farming in California’s Sacramento Valley. Researchers have focused on pest management systems and economics, changes in soil chemical properties with management, cover cropping strategies to enhance N availability, the role of soil microfauna in soil fertility, soil quality measurements, water-use efficiency, compost effects on root diseases, and management effects on soil biology and C and N cycling. The multidisciplinary nature of the SAFS project allows for the examination of trade-offs between such diverse areas as economics and soil quality or pest management and N dynamics. The broad scope of the project and the involvement of scientists, extension specialists, farmers, farm advisors, educators, and students brings a truly systems-oriented perspective to the research. Findings from the 12-year SAFS project include:

Pest Incidence and Management:
Root pathogens of tomato are affected more by rotation length than by management system. Some plant-parasitic nematodes are more abundant in the conventional than in the alternative systems. Nevertheless, arthropods, pathogens, and nematodes have had little influence on crop yields. In contrast, weeds have resulted in small but detectable yield loss in some years, particularly in the organic system.

Reducing Pesticide Use:
Pesticide use in corn, bean, and safflower grown in a four-year rotation could be reduced by 50% or more with little or no reduction in yield or increase in cost. In processing tomato total pesticide use could be reduced by 50% without yield or quality loss but premium prices are needed to compensate growers for increased pest management costs, primarily for weed management, which may average 50% more than conventional pest management costs.

Soil Quality:
In general, changes resulting from low-input and organic farming methods have positive, long-term effects on soil quality, including increased storage of plant nutrients and C, greater biological activity, and improved water infiltration. However, other changes present new management challenges, particularly during the transition, such as the slow or unpredictable N mineralization from organic sources.

Nitrogen Losses:
Nutrient budget and soil tests indicate that the conventional farming systems have been least efficient at storing excess N while the low-input farming system has been the most efficient. Thus, N losses have been greatest from the conventional, intermediate from the organic, and least from the low-input farming system.

Economic Viability:
Whole-farm profit comparisons demonstrate the economic incentive for a two-year rotation with tomato; a common cropping strategy in the Sacramento Valley. The primary concerns about this system are the potential for increased disease pressure and/or degradation of soil structure, which have become apparent at the SAFS site but not severely yield limiting. Among the four-year rotations in the SAFS study, the organic system with premium prices is the most profitable. Thus, it is a potentially viable farming system option for the Sacramento Valley with the current market demand for organic products.

Low-Input Corn:
Since 1992, when composted manure applications in the low-input corn system were replaced with supplemental inorganic nitrogen fertilizer, applied at about one-half the rate of the conv-4 system, yields have been consistently greater even though synthetic fertilizer N use has been 70-125 lbs/acre while that in the conv-4 corn system has been 160-200 lbs/acre. Cover crop residues have prevented the water infiltration problems observed under conventional management. Furthermore, the substitution of cultivation for some herbicide applications has reduced herbicide use and total pest management costs by 50%.

Cover Cropping and Nitrogen Management: Nitrogen availability has been an occasional problem in the organic corn and tomato systems of the SAFS project. A study examining possible solutions to this problem indicates that summer cover crops and fall irrigations promote bacteria-feeding nematode populations and N mineralization which leads to higher tomato yields.

Water Infiltration:
Under conventional management, water availability problems resulting from poor water infiltration have resulted in yield loss in at least some years, even with the use of deep tillage. Such problems have not occurred under organic or low-input management. Due to changes in soil physical properties resulting from cover cropping and organic matter increases, infiltration rates are over 50 percent higher in the organic and low-input systems. In the winter of 1999-2000, less than 15 percent of rainfall in these systems was lost as runoff, compared to 43 percent in the conventional systems. Soil water storage is significantly greater in the organic and low-input systems.

Energy Use: Based on output-input ratios, the low-input system is the most energy efficient farming system while the conv-2 system is the least efficient.


Click linked name(s) to expand
  • Kent Brittan
  • Peter Brostrom
  • Jim Durst
  • Howard Ferris
  • Willi Horwath
  • Leisa Huyck
  • Karen Klonsky
  • Tom Lanini
  • Jeff Mitchell
  • Gene Miyao
  • Bruce Rominger
  • Kate Scow
  • Ed Sills
  • Ariena van Bruggen


Materials and methods:

Site Description

The SAFS project, established in 1988, is located on an 11.3 ha site (38º 32’ N, 121º 47’ W, 18-m elevation) on the Agronomy Farm of the University of California, Davis. The region has a Mediterranean climate with most rainfall occurring during the winter months and relatively little during the growing season. Furrow irrigation is used for most crop production. Total annual rainfall is typically 400-500 mm and daytime temperatures during the growing season average 30-35°C. Soils at the site are classified as Reiff loam and Yolo silt loam.

Experimental Design
The SAFS project consisted of four experimental treatments which represent farming systems differing primarily in crop rotation and use of external inputs (Appendix B). The treatments included three, four-year rotations under conventional (conv-4), low-input, and organic management and one conventionally-managed, two-year rotation (conv-2). All three, four-year rotations included processing tomato, safflower, bean, and corn. In the conv-4 treatment, beans were double-cropped with winter wheat, while in the low-input and organic treatments, beans followed a biculture of oats and purple vetch which was either harvested for seed, cut as hay, or incorporated as green manure. Cover crops were grown during the winter preceding all other cash crops in the low-input and organic systems. The conv-2 treatment was a tomato and wheat rotation. There are four replications of each treatment and all possible crop rotation entry points were represented, resulting in a total of 56, 0.12-ha plots, arranged in a randomized block, split-plot design. A 3-ha companion area adjacent to the main site was used to address specific questions that emerged from the farming-systems comparisons.

All farming-system treatments used “best farmer management practices” which were determined through consultation with farmers and farm advisors participating in the project. The conv-4 and conv-2 treatments were managed with practices typical of the surrounding area, which included the use of synthetic fertilizers and pesticides. Decisions to use pesticides in these treatments were based upon common practices in the area as well as University of California IPM guidelines. In the low-input system, fertilizer and pesticide inputs were reduced primarily by using legume cover crops to improve soil fertility and mechanical cultivation for weed management. The organic system was managed according to the regulations of California Certified Organic Farmers (CCOF, 1995). Thus, no synthetic chemical pesticides or fertilizers were used. Instead, management included the use of cover crops, composted animal manure, mechanical cultivation, and limited use of CCOF-approved products.

Data Collection, Analysis, and Dissemination

Objective 1a-d: Farming-System Comparisons. Data on crop production, pest management, soil quality, and economics are collected and/or generated using appropriate methods (described below). Because research on dynamic agricultural systems typically creates some difficulties in clearly identifying the causes of observed patterns, a combination of simple statistical comparisons and multivariate analysis and modelling were used to describe and understand patterns and processes. Basic comparisons among cropping and farming systems were made using two-way analysis of variance, followed by mean separation tests when necessary. Interactions among factors and their associated effects on response variables were analyzed with linear and non-linear regression, principle components analysis, simulations, and other methods.

Objective 1a: Crop Production. Plant stand establishment and yield were measured for all cash crops in all of the farming-system treatments. Hand-harvested yields were used to verify machine-harvested yields and to measure residues returned to soil and harvest index. In addition, crop growth and nutrient uptake were monitored in tomato and corn throughout the growing season. Fruit quality was assessed at tomato harvest with visual scoring in the field and standard testing by a commerical laboratory. Management records were maintained for all field operations (tillage, planting, irrigation, etc.) and weather data (rainfall, temperature, evapotranspiration, etc.) were obtained from a permanent station adjacent to the field site.

Objective 1b: Pest Management.
Arthropod pests, weeds, plant-parasitic nematodes, and plant pathogens were monitored for research as well as management purposes. Arthropod pests and their natural enemies were monitored using sampling methods adapted from University of California IPM guidelines. Pest population data and recommended thresholds are used in determining the need for therapeutic management, such as pesticide applications. Weed populations and communities were assessed monthly with visual ground cover estimates and at crop harvest with biomass measurements. Plant-parasitic nematodes and root pathogens were measured with field damage scoring and laboratory isolation and identification. Current research emphases include an analysis of compost type on root pathogens, determination of the effects of plant N status on potato aphids, and refinement of potato aphid scouting methods.

Objective 1c: Soil Quality.
A wide array of chemical, biological, and physical soil properties were measured to assess short- and long-term effects of farming-system management on soil quality. Active soil N pools during the cash-crop growing season, including NO3-N, NH4-N, and potentially-mineralizable N, were intensively monitored with samples taken every 2-3 weeks in tomato and corn. Total N and C, pH, EC, CEC, and plant nutrients were measured less frequently to document longer-term trends. Soil biological properties studied include microbial biomass and diversity, nematode abundance and community composition, and measurements on macrofaunal abundance and diversity, including springtails (Collembola), ground beetles, and earthworms. Soil physical properities, including water stable aggregation, bulk density, penetration resistance, water infiltration rates, and water-holding capacity, were measured. Current research emphases include quantification of N cycling using 15N and determination of water budgets. An effort was also made to link the various soil quality measurements through the use of indexes in order to gain a greater understanding of the interrelationships among soil characterisics and processes.

Objective 1d: Economics.
The economic performance of each cropping system and farming system was quantified using the Budget Planner computer program (Klonsky and Cary, 1990). It was used to generate costs, returns, and profits and simulate the economic performance of a hypothetical 810-ha (2000 acre) farm. The actual costs of material inputs and labor were based upon current prices within the region. American Society of Agricultural Engineers (ASAE) formulas were used to calculate equipment costs for fuel, lubrication, and repair. The economics of field operations were derived from costs for labor, materials, and equipment; and field operation time is based on the use of commercial-sized equipment. This approach produces realistic budgets by accounting for the disproportionately large amount of time needed to manage small, experimental plots. All crop yields for the calculations were based upon experimental treatment means.

Objective 2: Low-Input and Organic Farming Tactics.
The SAFS companion area was used to test or develop practices or technologies that might be appropriate and useful in low-input and organic agriculture. This included replicated experiments and unreplicated trials on new cover crop varieties and mixtures, non-chemical weed management, conservation tillage practices, soil fertility and plant nutrition testing methods, and evaluation of insect pest control measures.

Objective 3: Information Dissemination.
Findings from the SAFS project were disseminated through presentations at professional and community meetings, newsletters, workshops, field tours, field days, peer-reviewed articles, student and researcher exchange programs, the web page (, and a video which is distributed by the University of California.

Meeting presentations: These included presentations at professional society meetings as well as presentations to local and statewide organzations promoting sustainable agriculture, farmland preservation, natural resource conservation, and youth education.

Newsletters: General newsletter topics included pest management, economics, soil biology, and low-input and organic production practices. The mailing list included 1500 members of the California agricultural community including farmers, farm advisors, and researchers.

Workshops: These were offered to provide intensive training to agricultural professionals in small groups (» 30) on topics including cover cropping, soil biology, and pest management.

Field tours: These were given throughout the year to small and large groups from industry, schools, government, extension, and universities. Hundreds of groups and individuals from over 30 countries visited the SAFS project.

Field days: The SAFS project held annual field days which continually increased in size and scope. The 1998 field day was combined with a UC Davis-sponsored event ‘AgTech’ including demonstrations, lectures, laboratories, an information fair, and a grower panel. Over 300 people attended, making this the largest field day in the history of the SAFS project.

Peer-reviewed articles: Research from the SAFS project was published in a variety of scholarly journals including Agronomy Journal, Soil Biology and Biochemistry, Agriculture Ecosystems & Environment, Applied Soil Ecology, and American Journal of Alternative Agriculture.

Research results and discussion:

Objective 1. Over a twelve-year period encompassing three, four-year rotation cycles, compare four farming systems with different levels of reliance on non-renewable resources with regard to:
a. Crop growth, yield, and quality as influenced by different pest management, agronomic and rotational schemes of the four farming systems.

Crop yields for the five cash crops of the 12-year SAFS study are summarized in Table 1 (Appendix A). From these data, it is apparent that crop production was very good for the duration of this trial, and representative of yields for those crops in the surrounding Yolo County area. The grand mean for crop yields (across all management systems and seasons) was above county averages for all of the five cash crops tested. The 28-acre experimental site has deep, fertile, and relatively uniform soils, and adequate, high-quality irrigation was available. All five cash crops studied in this experiment are commercially grown in Yolo County. The only significant crop production limitation attributable to the site is that of vertebrate pest management. We experienced periodic losses (ranging from reduced stand to entire plot decimation) to jack rabbits, ground squirrels, and crows. Because of the proximity of the University Farm to urban development, management tools available to most growers were not options for the project.

Analysis of variance for yield was performed on the combined data set for the 12 years of SAFS operation (Table 2, App. A). CV’s are reasonable for 1/3-acre plots. The higher CV for beans is in part a result of rabbit predation, but results for field beans will be discussed separately. Taken as a whole, the fact that low-input yields for tomato, safflower, and corn averaged 97, 84, and 108 percent of conventional is very respectable. Perhaps more surprising is the fact that those three crops, managed organically, yielded 88, 90 and 94 percent of conventional (Table 3). These data, over a 12-year period, and with a representative group of field crops, clearly refute figures currently cited by advocates of chemically intensive farming, as the only or best means of feeding a growing world population. This contradiction is more marked because the conventional yields herein reported are excellent, and above county averages that are high in their own right. Also, it should be noted that the average difference between yields of organic versus conventional are less than the year-to-year variation, as reflected in annual county averages for each crop.

From Table 2, it is clear that seasons, and systems, and season by system effects were all very significant. Several specific factors were observed to affect differentially the production of one or more crops in one or more of the alternative management systems. The following is a crop-by-crop account of the most significant factors observed during the 12 years of the study. It should be observed that from the outset, this study sought to make within-system adjustments to optimize system performance, rather than impose uniform management practices across systems for statistical reasons. The ultimate balancing factor was the differential production costs elicited by prioritizing “best farmer” practices for each of the systems. In some cases, our research group was able to agree that a certain production limitation was the unique result of researchers attempting to farm in a field station environment. In other cases, group opinion was divided between researchers of the above opinion, versus those who felt a particular production challenge was an inherent liability of that management system.

Tomatoes are the most vital economic determinant of the success or failure of the particular rotation and management systems studied. At the beginning of the experiment, a substantial percentage of the tomatoes in Yolo County were direct-seeded. Because of problems conserving soil moisture following the incorporation of winter cover crops (and our objective to produce tomatoes for the early harvest market), the challenges of obtaining adequate seedbed preparation, and the uncertainty of early spring weather, we elected to transplant the organic and low-input tomatoes beginning in 1992. With the exception of 1994, the soundness of that management decision was correct. In 1994, we experienced 100% transplant seedling infection by an insect-transmitted virus. The disease was not noticed before transplanting, but was later detected using ELISA methods, and led to crop decline during the season and reduced 1994 yield and quality in the organic and LI systems (Table 1). While it is doubtful that a commercial grower would accept and plant infected transplants without seeking economic compensation, neither yield nor economic adjustments were made for that loss.

Tomatoes also proved to be the crop most sensitive to harvest variables. Because the transplanted organic and LI tomatoes seldom matured at exactly the same time as the direct-seeded conventional-2 and conventional 4 crops, it was difficult to maintain exactly the same harvest conditions for all treatments. Also, 1/3-acre plots are quite adequate for commercial corn and safflower harvesting equipment, but less adequate for the several pieces of large harvesting equipment used for tomatoes. As a result, replicated hand-harvested subplot yields were sometimes used instead of full-plot mechanical yields, which generally showed a higher rep variability. The only statistically significant difference (p<.05) among tomato yields was the 4 ton/acre (12%) advantage of conventional-4 over organic tomatoes. As shown in the economic analysis, that difference was consistently offset by a larger price differential that favored the organic crop. Differences among other systems were not statistically significant. An interesting result emerged from analyzing 12 consecutive seasons of 2-year versus 4-year conventional tomato yields. While the 1.86 ton/acre difference in yield proved to not be statistically significant, project pathologists observed consistently greater incidence of root disease in the conventional-2 system (see section on diseases and pests). Most growers in the area cite the problems with tomato root health as a concern in “close” tomato rotations (many growers have found it economically attractive to grow tomatoes even more frequently than once every two seasons, as we did with our wheat/tomato 2-year conventional rotation). Safflower proved to be a reliable rotation crop in all 3 of the 4-year systems where it was included. Production costs are low, and safflower is recognized in California’s central valley for its ability to thoroughly dry the soil profile and thereby reduce the incidence of soil and water-borne diseases in subsequent crops of the rotation. Growers also like the fact that the safflower growing season (late winter through early summer) facilitates improved control of weed species that escape and build up in tomato, wheat, field bean, and corn systems. Further, in situations where irrigation water is limited or expensive, safflower requires little or no supplemental irrigation. The yield of conventional safflower was significantly better than those of the organic and LI systems (Table 2). Mean yields of all 3 systems were slightly higher than county averages for the 12 years of this study. The most significant challenges to consistent high yields in LI and organic safflower were seedbed preparation following cover crop management (especially issues of maintaining residual winter soil moisture to obtain good stand establishment, predation by seed corn maggot and jack rabbits, and timely, non-chemical control of weed and volunteer crop competitors. An example is “fiddleneck” (Amsinkia intermedia), a weed species apparently introduced through incompletely-composted manure. The seasons with relatively mediocre safflower yields in the alternative systems were those years where weather complicated cover crop management, planting and weed management, and in some cases replanting was required. In a chemical-free production system, safflower also has the potential to serve as a large reservoir of tarnished plant bugs (Lygus hesperus), which move to crops like tomatoes and field beans in July and August as the safflower dries down toward harvest. Safflower’s nitrogen requirements appear compatible with cover crop-driven production systems. Corn proved to be an excellent crop for the LI system, where yields were 8% better than conventional and significantly better (14%) than organic. This result is especially useful for growers interested in transitioning ground from conventional to LI or organic, and particularly if the grower plans to synchronize the rotation to capture organic premiums with tomatoes in the first eligible season of organically certified production. Most of the difficulties observed in producing corn with LI and organic management were similar to those noted above for safflower: seedbed preparation and moisture conservation following a winter cover crop, non-chemical weed management, modest seed corn maggot stand loss. However, nitrogen supply and irrigation management were also more important for the corn crop, and this affected the 3 systems in contrasting ways. As demonstrated in the section on soil-plant-water relations, cover cropped soils demonstrated water infiltration and retention characteristics very different than those of the conventional system. An attempt to convert the 3 corn systems from 30-inch beds with single rows, to 60-inch beds with double rows was abandoned midway through the 12 years because of the difficulty of supplying adequate moisture to the entire corn root system. At the conclusion of the 12-year experiment, it was obvious that the irrigation regime optimal for the LI and organic corn systems (more water, less frequently) was distinct from optimal management of the conventional system ( less water, but more often). Given the fact that efforts were made to maintain corn N supply constant across all systems, we attribute most of the yield differences between LI and conventional corn (which were especially consistent between 1992 and 1996) to differences in soil-water dynamics. Meeting the corn crop nitrogen requirements (amount and timing), proved much simpler for LI supplementation (cover crop N plus synthetic fertilizer) than for the organic system (cover crop supplemented with composted manures). Incomplete incorporation of cover crop residues sometimes led to problems for non-chemical weed management, such that optional use of a post-emergent, contact herbicide was especial

Research conclusions:

The effects of organic and low-input farming methods on crop yields have important implications for the adoption of these methods by farmers, governmental support for research, development, and extension, and the supply and security of food at local, regional, and global scales if such practices become more widely used. Researchers considering the effects of widespread adoption of organic and low-input methods on food production have come to varied conclusions ranging from little or no yield reduction to catastrophic crop losses (Pimentel 1993, Loomis and Connor 1992, Pimentel et al. 1993, Bender 1994, Knutson et al. 1994). Based on 205 comparisons from the literature, mainly from northern Europe and North America, Stanhill (1990) found that the productivity of organic crop and animal production systems averaged about 10% less than comparable conventional systems. While this generalized finding is important and insightful, systems comparisons for specific regions and crops are necessary because of geographic differences in farming practices, soils, climate, pest pressures, and other factors.
Thus the findings of the SAFS project that for four commodity crops, organic methods resulted in yields about 10-12 percent less than conventional methods, and that differences between years are greater than differences between systems, are extremely important. Of further importance is the fact that for yield and price comparisons, the same cultivar of each crop is grown across all farming systems. Since most available cultivars are selected for conventional production, they may maximize access to nutrients and water applied at the surface and not have the optimum root morphology to access deeper distribution of minerals and water in low-input and organic systems. Thus, the organic and cover-cropped systems may not even be performing at their optimum levels.
In a survey of USDA-funded research pertaining to organic agriculture, the Organic Farming Research Foundation lauded three SAFS-associated projects as the “state-of-the-art of university-based organic farming systems research” throughout the entire U.S. The project has positively impacted farming practices and agricultural communities in the Sacramento Valley, the state, the nation, and many countries around the world. These changes include: a greater interest in cover crops, legumes and crop rotations; increased organic acreage of field crops; increased monitoring by growers of water use/efficiency, pest thresholds and soil and crop nitrogen requirements; a growing recognition of the importance of soil ecology; and heightened interest in a more holistic view of soil quality.
In summary, the SAFS project has specifically demonstrated that it is profitable to grow tomatoes organically; that yields can be maintained in organic and low-input systems; that pesticide use can be reduced by half with little or no decrease in yields; and that cover-cropping can provide multiple important benefits, including sequestration of carbon, decreased nitrogen leaching, increased infiltration and decreased runoff, and improved soil quality.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

SAFS Publications

Andrews, S.S., D.L. Karlen, J.P. Mitchell. 2002. A comparison of soil quality indexing methods for vegetable production systems in Northern California. Agriculture, Ecosystems and Environment 90:25-45.
Bongers, T., and H. Ferris. 1999. Nematode community structure as a bioindicator in environmental monitoring. Trends in Evolution and Ecology 14:224-228.
Bossio, D.A., K.M. Scow. 1998. Impacts of Carbon and flooding on soil microbial communities: phospholipid fatty acid profiles and substrate utilitzation patterns. Microbial Ecology 35: 265-278.
Bossio, D.A., and K.M. Scow. 1995. Impact of carbon and flooding on the metabolic diversity of microbial communities in soil. Appied Environmental Microbiology 61:4043-4050.
Bruns, M.A., and K.M. Scow. 1999. DNA fingerprinting as a means to identify sources of soil-derived dust: problems and potential. p. 193-205. In: Scow et al. (eds) Integrated assessment of ecosystem health. Lewis Publishers, Boca Raton, FL.
Bruns, M., K.J. Graham, K.M. Scow, and T. VanCuren. 1998. Biological markers to characterize potential sources of soil-derived particulate matter. Air Waste Manag. Assoc. Proc.
Cavero, J., R.E. Plant, C Shennan, D.B. Friedman, J.R. Williams, J.R.Kiniry, K.W. Benson. 1999. Modeling Nitrogen cycling in safflower and tomato wheat rotations. Agricultural Systems 60: 123-135.
Cavero, J., R.E. Plant, C. Shennan and D.B. Friedman. 1997. The effect of nitrogen source and crop rotation on the growth and yield of processing tomatoes. Nutrient Cycling in Agroecosystems 47: 271-282.
Cavero, J., R.E. Plant, C. Shennan, J.R. Williams, J.R. Kiniry and V.W. Benson. 1998. Application of EPIC model to nitrogen cycling in irrigated processing tomatoes under different management systems. Agricultural Systems 56(4):391-414.
Chen, J., H. Ferris, K. M. Scow, K.J. Graham. 2001. Fatty acid composition and dynamics of selected fungal-feeding nematodes and fungi. Comparative Biochemistry and Physiology 130: 135-144.
Chen, J and H. Ferris. 1998. Mineralization of nitrogen by Aphelenchoides composticola. Journal of Nematology 30:490 (abstr.)
Chen, J. and H. Ferris. 1999. The effects of nematode grazing on nitrogen mineralization during fungal decomposition of organic matter. Soil Biology and Biochemistry 31:1265-1279.
Chen, J. and H. Ferris. 2000. Growth and nitrogen mineralization of selected fungi and fungal-feeding nematodes on sand amended with organic matter. Plant and Soil 218:91-101.
Chen, J. and H. Ferris. 1997. Nitrogen mineralization by Aphelenchus avenae associated with Rhizoctonia spp. and barley straw. Journal of Nematology 29: 572 (abstr.)
Clark, M. S., W. R. Horwath, C. Shennan, K. M. Scow. 1998. Changes in soil chemical properties resulting from organic and low-input farming practices. Agronomy Journal. 90: 662-671.
*Clark, M. S., H. Ferris, K. Klonsky, W.T. Lanini, A.H.C. vanBruggen, & F.G. Zalom. 1998. Agronomic, economic, and environmental comparison of pest management in conventional and alternative tomato and corn systems in northern California. Agriculture, Ecosystems & Environment 68:51-71.
*Clark, S., K. Klonsky, P. Livingston, and S. Temple. 1999. Crop-yield and economic comparisons of organic, low-input, and conventional farming systems in California’s Sacramento Valley. American Journal of Alternative Agriculture 14: 109-121.
Clark, M.S. 1999. Ground beetle abundance and community composition in conventional and organic tomato systems of California’s Central Valley. Applied Soil Ecology 11:199-206.
Clark, M.S., W.R. Horwath, C. Shennan, K.M. Scow, W.T. Lanini, and H. Ferris. 1999. Nitrogen, weeds and water as yield-limiting factors in conventional, low-input, and organic tomato systems. Agriulture, Ecosystems, Environment 73: 257-270.
Colla, G., J.P. Mitchell, D.D. Poudel, S.R. Temple. 2002 Changes of tomato yield and fruit elemental composition in conventional, low-input and organic systems. Journal of Sustainable Agriculture 20(2) 53-67.
Colla, G., J.P. Mitchell, D.D. Poudel, F Saccardo. 2001. Impacts of farming systems and soil characteristics on processing tomato fruit quality. Proceedings from the 7th Symposium on Processing Tomato 333-341.
Colla, G., J.P. Mitchell, B.A. Joyce, L.M. Huyck, W.W. Wallender, S.R. Temple, T. C. Hsiao, and D.D. Poudel. 2000. Soil physical properties, tomato yield and quality in alternative cropping systems. Agronomy Journal 92(5):924-932.
Ferris, H., T. Bongers, R. G. M. de Goede. 2000. A framework for soil food web diagnostics: extension of the nematode faunal analysis concept. Applied Soil Ecology. In Press.
Ferris, H., T. Bongers, R. G. M. de Goede. 1999. Nematode faunal indicators of soil food web condition. Journal of Nematology 31(4) 534-535.
Ferris, H., R. C. Venette, H. R. van der Meulen and K. M. Scow. 1998. Nitrogen fertility and soil food web management. Journal of Nematology 30:495-496.
Ferris, H., T. Bongers and R. G. M. de Goede. 1999. Nematode faunal indicators of soil food web condition. Journal of Nematology 31:534-535 (abstract).
Ferris, H., R.C. Venette, H.R. van der Meulen, S.S. Lau. 1998. Nitrogen mineralization by bacterial-feeding nematodes: Verification and measurement. Plant and Soil 203:159-171
Ferris, H., R. C. Venette, H. R. van der Meulen, and S. S. Lau. 1997. Nitrogen mineralization by bacterial-feeding nematodes. Journal of Nematology 29: 577 (abstr.)
Ferris, H., R. C. Venette, and S. S. Lau. 1997. Population energetics of bacterial-feeding nematodes: Carbon and nitrogen budgets. Soil Biology and Biochemistry 29: 1183-1194.
Ferris, H., M. Eyre, R. C. Venette, and S. S. Lau. 1996. Population energetics of bacterial-feeding nematodes: stage-specific development and fecundity rates. Soil Biology and Biochemistry 28: 271-280.
Ferris, H., R. C. Venette and S. S. Lau. 1996. Dynamics of nematode communities in tomatoes grown in conventional and organic farming systems, and their impact on soil fertility. Applied Soil Ecology 3: 161-175.
Ferris, H., S. Lau, and R. Venette. 1995. Population energetics of bacterial-feeding nematodes: respiration and metabolic rates based on carbon dioxide production. Soil Biology and Biochemistry 27:319-330.
Ferris, H., R. C. Venette, S. A. Lau, K. M. Scow, and N. Gunapala. 1994. Bacterial feeding nematodes in organic and conventional farming systems. Journal of Nematology 26:544 (abstr.).
Fuller, M.E., and K.M. Scow. 1997. Impacts of trichloroethylene (TCE) and toluene on nitrogen cycling in soil. Appl. Environ. Microbiol. 63(10):4015-4019.
Fuller, M.E., K.M. Scow, S.S. Lau and H. Ferris. 1997. Trichloroethylene (TCE) and toluene effects on the structure and function of the soil community. Soil Biology and Biochemistry 29(1):75-89.
Gaskell, Mark, Benny Fouche, Steve Koike, Tom Lanini, Jeff Mitchell and Richard Smith. 2000. Organic vegetable production in California – Science and practice. Hort Technology. 10(4);699-713.
Grünwald, N. J., S. Hu and A. H. C. van Bruggen. 2000. Short-term cover crop decomposition in organic and conventional soils; Characterization of soil C, N, microbial and plant pathogen dynamics. European Journal of Plant Pathology 106: 37-50.
Grünwald, N. J., S. Hu and A. H. C. van Bruggen. 2000. Short-term cover crop decomposition in organic and conventional soils: Soil microbial and nutrient cycling indicator variables associated with different levels of soil suppressiveness to Pythium aphanidermatum. European Journal of Plant Pathology 106:51-65.
Gunapala, N. and K.M. Scow. 1998. Dynamics of soil microbial biomass and activity in conventional and organic farming systems. Soil Biology and Biochemistry 30:805-816.
Gunapala, N., R.C. Venette, H. Ferris, and K.M. Scow. 1998. Effects of soil management history on the rate of organic matter decomposition. Soil Biology and Biochemistry 30:1917-1927.
Hadas, A. T.A. Doane, A.W. Kramer, C. van Kessel, W.R. Horwath. 2002. Modelling the turnover of 15N-labelled fertilizer and cover crop in soil and its recovery by maize. European Journal of Soil Science 53: 541-552.
Horwath, W.R., O.C. Devevre, T.A. Doane, and D.D. Poudel. Defining changes in soil organic matter quality during the transition from conventional to low-input and organic systems to identify sustainable farming practices. Submitted.
Hu, S.J., van Bruggen, A.H.C., and Grünwald, N.J. 1999. Dynamics of bacterial populations in relation to carbon availability in a residue-amended soil. Applied Soil Ecology. 13:21-30.
Hu, S.J., and A.H.C. van Bruggen. 1998. Efficiencies of chloroform fumigation in soil:effects of physiological states of Bacteria. Soil Biology and Biochemistry 30(13): 1841-1844.
Hu, S.J., and A.H.C. van Bruggen,R.J. Wakeman, N.J. Grünwald. 1997. Microbial suppression of in vitro growth of Pythium Ultimum and disease incidence in relation to soil C and N availability. Plant and Soil 195: 43-52.
Jaffee, B.A., H.Ferris, and K.M. Scow. 1998. Nematode-trapping fungi in organic and conventional cropping systems. Phytopathology 88:344-349.
Johnson, C.R., and K.M. Scow. 1999. Effect of nitrogen and phosphorus addition on phenanthrene biodegradation in four soils. Biodegradation 10:43-50.
*Joyce, B.A., W.W. Wallender, J.P. Mitchell, L.M. Huyck, S.R. Temple, P.N. Brostrom and T.C. Hsiao. 2002. Infiltration and soil water storage under winter cover cropping in California’s Sacramento Valley. Trans. ASAE 45(2): 315-326.
*Klonsky, K. and P. Livingston. 1994. Alternative systems aim to reduce inputs, maintain profits. California Agriculture. 48(5): 34-42.
Kramer, A.W., T.A. Doane, W.R. Horwath, C. van Kessel. 2002. Combining fertilizer and organic inputs to synchronize N supply in alternative cropping systems in CA. Agriculture Ecosystems and Environment 91:233-243.
*Lanini, W.T., F. Zalom, J.J. Marois, and H. Ferris. 1994. Researchers find short-term insect problems, long-term weed problems. California Agriculture 48(5):27-33.
Lau, S.S., M.E. Fuller, H. Ferris, R.C. Venette, and K.M. Scow. 1997. Development and testing of an assay for soil-ecosystem health using the bacterial-feeding nematode Cruznema tripartitum. Ecotoxicology and Environmental Safety 36:133-139.
Lundquist, E.J., L.E. Jackson, and K.M. Scow. 1999. Wet-dry cycles affect dissolved organic carbon in two California agricultural soils. Soil Biology and Biochemistry 31:1031-1038.
Lundquist, EJ; Scow, KM; Jackson, LE; Uesugi, SL; Johnson, CR. 1999. Rapid response of soil microbial communities from conventional, low input, and organic farming systems to a wet/dry cycle. Soil Biology and Biochemistry 31:1661-1675.
Lundquist, E.J., L.E. Jackson, K.M. Scow, and C. Hsu. 1999. Changes in microbial biomass and community composition, and soil carbon and nitrogen pools after incorporation of rye into three California agricultural soils. Soil Biology and Biochemistry 31:221-236.
*Poudel, D.D., W.R. Horwath, W.T. Lanini, S.R. Temple, AHC van Bruggen. 2002 Comparison of soil N availability and leaching potential, crop yields, and weeds in organic, low-input and conventional farming systems in Northern Califronia. Agriculture Ecosystems and Environment 90:125-137.
*Poudel, D.D., W.R. Horwath, J.P. Mitchell, and S.R. Temple. 2001. Impacts of farming systems on soil mineral nitrogen storage and loss. Agricultural Systems 68(3): 253-268.
*Poudel, D.D., H. Ferris, K. Klonsky, W.R. Horwath, K.M. Scow, A.H.C. van Bruggen, W.T. Lanini, J.P. Mitchell, S.R. Temple. 2001. The Sustainable Agriculture Farming Systems Project in California’s Sacramento Valley. Outlook on Agriculture 30(2): 109-116.
Scow, K.M. 1999. Soil microbiology. In: Encyclopedia of Microbiology. Academic (in press).
Scow, K.M., Freidman, D. J. Mitchell, H. Ferris, T. Kearney, K. Klonsky, T. Lanini, A.H.C. van Bruggen, T. Miller, G. Miyao, B.Rominger, C. Shennan, E. Sills, D. Stewart, S.R. Temple, F. Zalom. 1996. Impact of microbial processes on crop use of fertilizers from organic and mineral sources. Proceedings of the 4th annual fertilizer research and education program conference. Modesto, California October 1996.
Scow, K.M., O. Somasco, N. Gunapala, S. Lau, R. Venette, H. Ferris, R. Miller, and C. Shennan. 1994. Transition from conventional to low-input agriculture changes soil fertility and biology. California Agriculture 48(5):20-26.
Scow, K.M. 1997. Soil microbial communities and carbon flow in agroecosystems, p. 361-407. In: Jackson, L.E.(ed.) Ecology in Agriculture. Academic Press, N.Y.
Scow, K. M. 1997. Interrelationships between microbial dynamics and carbon flow in agroecosystems. In: Jackson, L.E. (ed.) Agricultural Ecology.
Semenov, A. M., A. H. C. van Bruggen, and V. V. Zelenev. 1999. Moving waves of bacterial populations and total organic carbon along roots of wheat. Microbial Ecology 37:116-128.
Shouse, B. N. and H. Ferris. 1999. Microbe-grazer-predator community dynamics during organic matter decomposition. Journal of Nematology 31:570 (abstr.)
Song, XH; Hopke, PK; Bruns, MA; Graham, K; Scow, K. 1999. Pattern recognition of soil samples based on the microbial fatty acid contents. Environmental Science and Technology 33:3524-3530.
Sudarshana, P., J.R. Hanson, and K.M. Scow. 1999. Application of random amplified polymorphic DNA (RAPD) method for characterization of soil microbial communities. In: Scow et al. (eds) Critical methodologies for the study of ecosystem health. Lewis Publishers, Boca, Raton, FL.
*Temple S.R., O.A. Somasco, M. Kirk and D. Friedman. 1994. Conventional, low-input, and organic farming systems compared. California Agriculture. 48(5): 14-19.
*Temple, S.R., D.B. Friedman, O. Somasco, H. Ferris, K. Scow, and K. Klonsky. 1994. An interdisciplinary, experiment station-based participatory comparison of alternative crop management systems for California’s Sacramento Valley. Amer. J. Altern. Agric. 9:64 -71.
Temple, S.R. and W.C. Leibhardt. A processing tomato rotation: Comparisons of organic and conventional farming systems in California’s Sacramento Valley. Proceedings of the 13th Annual IFOAM Scientific Conference.
van Bruggen, A.H.C. 1995. Plant disease severity in high-input compared to reduced input and organic farming systems. Plant Disease 79:976-984.
Venette, R.C., and H. Ferris. 1998. Influence of bacterial type and density on population growth of bacterial-feeding nematodes. Soil Biology and Biochemistry 30:949-960.
Venette, R.C., F.A. M. Mostafa, and H. Ferris. 1997. Trophic interactions between bacterial feeding nematodes and the nematophagous fungus Hirsutella rhossiliensis in plant rhizospheres to supress Heterodera schachtii. Plant and soil 191:213-223.
Venette, R. C. and H. Ferris. 1997. Thermal restraints to population growth of bacterial-feeding nematodes. Soil Biology and Biochemistry 29-63-74.

*List of SAFS Newsletters

Clark, M.S., T. Lanini, K. Klonsky. 1998. Weed Management Practices in Organic and Low-Input Farming Systems. Sustainable Agriculture Farming Systems Project Bulletin 2 (2): 1-3.
Clark, M.S., K. Scow, H. Ferris, S. Ewing, J. Mitchell, W. Horwath. 1998. Evaluating soil quality in Organic, Low-Input, and Conventional Farming Systems. Sustainable Agriculture Farming Systems Project Bulletin 2 (1): 1-3.
Clark, M. S., H. Ferris, K. Klonsky, W.T. Lanini, A.H.C. van Bruggen, F.G. Zalom, S. Temple. 1997. Pesticide use reduced by 50-100% in low-input and organic cropping systems. Sustainable Agriculture Farming Systems Project Bulletin 1 (3): 1-3.
Ferris, H., K. Scow, S. Temple, M. Espley, R. Venette. 1996. Introduction to the SAFS Project. Sustainable Agriculture Farming Systems Project Bulletin 1 (1): 1-3.
Friedman, D., R. Miller, S. Temple, T. Kearney, M. Espley. 1997. Low-input corn production yields good crop, better returns, and improved soil quality. Sustainable Agriculture Farming Systems Project Bulletin 1 (2): 1-3.
Klonsky, K., M. S. Clark, P. Livingston. 1997. Economic viability of organic and low-input farming systems in Sacramento Valley. Sustainable Agriculture Farming Systems Project Bulletin 1 (4): 1-3.
Poudel, D.D., W.R. Horwath, J.P. Mitchell, S.R. Temple. 1999. Impacts of Farming System on Soil Mineral Nitrogen Levels of Irrigated Processing Tomatoes: A Case Study from the UC Davis Sustainable Agriculture Farming Systems Project. Sustainable Agriculture Farming Systems Project Bulletin 3 (1): 1-3.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.