Sustainable Agriculture Farming
Systems Project (SAFS)

  * Historical Data *  

Publication Abstracts

M. S. Clark, H. Ferris, K. Klonsky, W.T. Lanini, A.H.C. vanBruggen, and 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, and Environment 68:51-71

The effectiveness, economic efficiency, and environmental impact of pest management practices was compared in conventional, low-input, and organic processing tomato and field corn systems in northern California. Pests, including arthropods, weeds, pathogens, and nematodes, were monitored over an eight-year period. Although both crops responded agronomically to the production-system treatments, arthropods, pathogens, and nematodes were found to play a relatively small role in influencing yields. In contrast, weed abundance was negatively correlated with tomato and corn yields and appeared to partially account for lower yields in the alternative systems compared to the conventional systems. Lower pesticide use in the organic and low-input systems resulted in considerably less potential environmental impact but the economic feasibility of reducing pesticide use differed dramatically between the two crops. The performances of the organic and low-input systems indicate that pesticide use could be reduced by 50% or more in corn with little or no yield reduction. Furthermore, the substitution of mechanical cultivation for herbicide applications in corn could reduce pest management costs. By contrast, pesticide reductions in tomato would be economically costly due to the dependence on hand hoeing as a substitution for herbicides. Based on the performance of the low-input and organic tomato systems, a 50% pesticide reduction would increase average pest management costs by 50%.


M.S. Clark, W.R. Horwath, C. Shennan, and K.M. Scow. 1998. Changes In Soil Chemical Properties Resulting From Organic And Low-Input Farming Practices. Agronomy Journal (in press)

Soil chemical properties were studied during the transition from conventional to organic and low-input farming practices over an 8-yr period at the Sustainable Agriculture Farming Systems Project in California's Sacramento Valley to document changes in soil fertility status and nutrient storage. Four farming systems which differed in crop rotation and the use of external inputs were established on land that had been previously managed conventionally. Fertility in the organic system depended upon animal manure applications and winter cover crops while the two conventional systems received synthetic fertilizer inputs. The low-input system was managed using cover crops and animal manure during the first 3 yr and with cover crops and synthetic fertilizer for the remaining 5 yr. Soil chemical properties were compared 4 and 8 yr after establishment. Most of the observed changes in soil chemical properties were consistent with predictions based upon nutrient budgets. Inputs of C, P, K, Ca, and Mg were higher in the organic and low-input systems as a result of manure applications and cover crop incorporations. After 4 yr of production, soils in the organic and low-input systems had higher soil organic C, soluble P, exchangeable K, and pH. Discontinuation of manure applications in the low-input system in year 4 resulted in declining levels of organic C, soluble P, and exchangeable K in low-input farming system. Differences in crop rotation also had a significant effect on organic C levels due to the presence or absence of corn in the cropping sequence. Differences in total N appeared to be related partially to inputs, however, differences in the efficiency of the farming systems to store excess N inputs were also suggested. The low-input system appeared to be most efficient in storing excess N, while the conventional systems were least efficient. Electrical conductivity (EC), soluble Ca, and soluble Mg levels were tightly linked but not consistently different among treatments. Relatively stable EC levels in the organic system indicated that the use of animals manures has not resulted in increased salinity. Overall, the findings of this study indicate that organic and low-input farming in the Sacramento Valley result in small but important increases in soil organic C and larger pools of stored nutrients which are critical for long-term fertility maintenance.


N. Gunapala And K. M. Scow. 1998. Dynamics Of Soil Microbial Biomass And Activity In Conventional And Organic Farming Systems. Soil Biology and Biochemistry (in press)

Dynamics of microbial communities during two growing seasons were compared in soils under tomatoes managed by conventional (2-and 4 -y rotations), low imput, or organic practices. Fumigation extractable carbon (FEC) and nitrogen (FEN), potentially mineralizable N, arginine ammonification and substrate induced respiration (SIR) were significantly higher in organic and low input than conventional systems on most sample dates. Microbial variables were significantly negatively correlated with amount of soil mineral N in the conventional 4 y system , whereas they were positively correlated with mineral N in the organic system. The C-to-N rations of material released after fumigation extraction were significantly higher in the conventional than organic soils. In all farming systems, soil moisture was positively correlated with FEC or FEN, but negatively correlated with the C-to-N ratio of the microbial biomass and SIR. Soil temperature was negatively correlated with FEC and FEN, but positively correlated with the C-to-N ratio of microbial biomass.


M. Sean Clark. 1998. Ground Beetle Abundance and Community Composition in Conventional and Organic Tomato Systems of California's Central Valley. Applied Soil Ecology (in Press)

Ground beetle abundance and community characteristics were compared in tomato systems under conventional and organic management. Beetles were sampled with pitfall traps over a 10-mo period during 1997 in plots that had been under consistent management at the University of California at Davis since 1988. Abundance and species richness were greater in the organic system compared to the conventional system. Six of the 17 species collected were found only in organically-managed plots. However, no differences in species diversity or evenness according to the Shannon and Simpson indices were found. These results were found to be consistent with those of most other studies on ground beetle communities in conventional and organic annual cropping systems.


D.A. Bossio, K.M. Scow, N. Gunapala, K.J. Graham. 1997. Determinants of Soil Microbial Communities: Effects of A agricultural Management, Season, and Soil Type on Phospholipid Fatty Acid Profiles. Microbial Ecology 36:1-12

Phospholipid fatty acid (PLFA) profiles were measured in soils from organic, low-impute, and conventional farming systems that are pert of the long term Sustainable Agriculture Farming Systems (SAFS) project. The farming systems differ in whether their source of fertilizer is mineral or organic, and in whether a winter cover crop is grown. Sustained increases in microbial biomass resulting from high organic matter inputs have been observed in the organic and low-input systems. PLFA profiles were compared to ascertain whether previously observed changes in biomass were accompanied by a change in the composition of microbial community. In addition, the relative importance of environmental variables on PLFA profiles was determined. Reduce analysis ordination showed that PLFA profiles from organic and conventional systems were significantly different from April to July. On ordination plots, PLFA profiles from the low-impute system fell between organic and conventional systems on most sample dates. A group of fatty acids ( i14:0, a15:0, 16:1w7c, 16:1w5c, 14:0, and 18:2w6c) was enriched in the organic plots throughout the sampling period, and another group (10ME16:0,20H 16:1and ME17:0 ) was consistently lower in relative abundance in the organic system. In addition, another group (15:0,a17:0, i16:0, 17:0 and 10Me18:0) was enriched over the short term in the organic plots after compost incorporation. The relative importance of various environmental variables in governing the composition of microbial communities could be ranked in the order: soil type > time > specific farming operation (e.g., cover crop incorporation or sidedressing with mineral fertilizer) > management system > spatial variation in the field. Measures of the microbial community and soil properties (including microbial biomass carbon and nitrogen, substrate induced respiration, basal respiration, potentially mineralizable nitrogen, soil nitrate and ammonium, and soil moisture) were seldom associated with the variation in the PLFA profiles.


J. Cavero, R.E. Plant, C. Shennan. 1996. The Effect Of Nitrogen Source And Crop Rotation On The Growth And Yield Of Processing Tomatoes.

Vegetable crops such as processing tomatoes (Lycopersicon esculentum MILL) are usually complex in terms of nitrogen (N) dynamics because of the large amounts absorbed by the crop, the short growing season and the use of irrigation. Complexity increases when N is supplied from an organic source. A crop simulation model could be very useful to improve N management in this crop. Processing tomatoes were grown on raised beds and furrow irrigated in 1994 and 1995 in the Sacramento Valley of California. Fertilizer N and/or purple vetch (Vicia sativa L. ) as green manure and composed turkey manure were used as sources of N. The Erosion productivity Impact Calculator (EPIC) model was calibrated with 1994 data and validated with 1995 data. Plant growth was accurately simulated in the conventional systems that used fertilizer N and in the low input system that used fertilizer N plus vetch. The model accurately simulated above-ground biomass in a system that used vetch and no synthetic fertilizer N, but it over-predicted Leaf Area Index (LAI). Nitrogen deficiency was observed in the plants in this system. The model simulated nitrogen deficiency mainly as a reduction in biomass production but in the real world the reduction of leaf area was the first effect of nitrogen deficiency in the vegetative phase. Yields were accurately predicted except when diseases e.


Ferris, H. 1992. New frontiers in nematode ecology. Journal of Nematology 25:374-382.

Future areas of emphasis for research and scholarship in nematode ecology are indicated by pressing agricultural and environmental issues, by new directions in applied Nematology, and by current technological advances. Studies in nematode ecology must extend beyond observation, counting, and simple statistical analysis. Experimentation and the testing of hypotheses are needed for understanding the biological mechanisms of ecological systems. Opportunities for fruitful experimentation in nematode ecology are emerging at the ecosystem, community, population, and individual levels. Nematode ecologists will best promote their field of study by closely monitoring and participating in the advances, initiatives, developments, and directions in the larger field of ecology.

Key words: Approach, biodiversity, concept, level of organization, population regulation, scale, theory, trophic roles, variability.
Department of Nematology 25:374-382(Abstr.)., University of California, Davis, CA 95616.


Ferris, H., R. C. Venette, S. A. Lau, K. M. Scow, and N. Gunapala. 1994. Bacterial-feeding nematodes in conventional and organic farming systems. Journal of Nematology 26:544. (Abstr.).

We investigated temporal relationships among bacterial-feeding nematodes, (BFN), fertility, and microbial biomass in soils managed under conventional and organic farming systems. There were more BFN in the conventional than the organic plots in the early spring, but numbers were greater in the organic plots following incorporation of a winter cover crop. Numbers of BFN in the organic plots were positively correlated with measures of microbial abundance and activity, including microbial biomass carbon, microbial biomass nitrogen, and substrate-induced respiration. These correlations were not significant in the conventional plots. The BFN community was less diverse in the organic than in the conventional plots due to temporal predominance of individual species, which was related to temperature-niche characteristics of the species. Temporal predominance influences the contribution of BFN species to nitrogen mineralization during key periods of plant growth.

Department of Nematology 26:544. (Abstr.)., University of California, Davis, CA 95616.


Ferris, H. and S. Lau. 1992. Respiration rates of microbivorous nematodes. Journal of Nematology 24:589. (Abstr.).

Temperature-dependent respiration rates were determined from CO2 evolution of populations on pH-buffered gel in sealed chambers. Chambers were maintained at constant temperature and flushed with CO2-free air before respiration measurements. The air above the gel surface in each chamber was circulated through an infrared gas analyzer before and after 30 min. respiration periods to measure change in gas concentration. Respiration of associated bacteria was adjusted using CO2 evolution from nematode-free bacteria control flasks. Total nematode biomass in each chamber was estimated from length and width measurements of a representative sample. CO2 evolution rates were standardized for age structure of the test population. Rates ranged from approximately 0.005 mg CO2 per mg nematode per hour at 15 C to 0.024 at 26 C for Cruznema tripartitum and 0.028 at 30 C for Acrobeloides bodenheimeri. These two species, differing in thermal maxima for respiration rates, were obtained from the same field soil. Respiration rates for a laboratory population of Caenorhabditis elegans were comparable, with a maximum at 25 C. Because respiratory rates per unit biomass are similar, participation of these nematodes in energy flow in an ecosystem is a function of size of individuals, and of individual and population growth rates.

Department of Nematology 24:589. (Abstr.)., University of California, Davis, CA 95616.


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 (Abstr.).

Nematode communities were monitored intensively through a tomato (Lycoperscion esculentum L.) growing season in plots managed by conventional and organic farming practices. The temporal dynamics of individual species of bacterial feeding nematodes differed and suggested differing importance of species in their contribution to N-mineralization in the organically managed soil. Species with r-selected , colonizer characteristics were most responsive to incorporation of organic matter and the subsequent increase of microbial biomass. Bacterial feeding nematode populations were lowest early in the growing season when tomato plants exhibited symptoms of nitrogen deficiency. We hypothesize that increasing abundance, biomass, and activity of these nematodes in the spring by organic matter incorporation at the end of the previous crop would reduce the observed nitrogen stress. Fungal feeding nematodes were more abundant in the conventional than the organic plots during the periods of organic matter decomposition, possibly related to the higher carbon:nitrogen ratios of the crop residues incorporated into the conventional soils than of the manures and leguminous cover crops incorporated into the organic soils. Predaceous and omnivore nematode populations were low in both farming systems, and plant-parasitic nematode species reflected the crop sequences in rotations used in each system.

Key Words : Bacterial-feeding Nematodes; Soil Fertility; Nematode Community dynamics; Nematode abundance and biomass.


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 (3): 271-280, (Abstr.).

By grazing on bacteria, bacterial feeding nematodes participate in decomposition food webs and N mineralization to an extent determined by metabolic and behavioral attributes and by life history. We determined the stage-specific development and fecundity rates for eight species on a physiological time scale to allow time and temperature-varying predictions of population progressions. Development from egg to adult of four species in the Rhabditidae (Bursilla labiata, Caenorhabditis elegans, Cruznema tripartitum and Rhabditis cucumeris) was faster than that for three species in the Cephalobidae (Acrobeloides bodenheimeri, A. buetschlii and Cephalobus persegnis) on a Julian time (calendar) basis at 20 degrees C. Development in the Rhabditidae was generally faster on a physiological (degree-day) time scale as well, but those times are not directly comparable as the basal threshold for degree-day (DD) accumulation differed among species. The fecundity period for females of the seven species varied between 55 and 75% of the total duration of the life course, during which they produced between 125 eggs (B. labiata) and 567 eggs (C. tripartitum). Simulated population growth under favorable temperature conditions, using parameter values determined in these studies, indicated rapid population growth in the large-bodied , highly-fecund rhabiditid species (R. cucumeris and C. tripartitum). Population growth was intermediate in the small-bodied , less-fecund rhabiditids with short egg production periods ( B. labiata), slower in the cephalobids (A. bodenheimeri and A. buetschlii ) and slowest in C. persegnis. R. cucumeris spent a greater portion of its development time in the egg stage than did any of the other species.


Klonsky, K. and P. Livingston. 1994. Alternative systems aim to reduce inputs, maintain profits. California Agriculture. 48(5): 34-42.



Ventette, R.C. H. Ferris, 1996. Thermal constraints to population growth of bacterial-feeding nematodes. Soil Biol. Biochem. 29 (1): 63-74.

Bacterial feeding nematodes are important participants in decomposition pathways and nutrient cycles in soils. The contribution of each species to component processes depends upon the physiology of individuals and the dynamics of populations. Having determined the effects of temperature on metabolic rates of several species of bacterial-feeding nematodes, we now present the effects of temperature on population growth rates and relate those to observed field dynamics..


Cavero J., R.E. Plant, C. Shennan, and D. 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.

Four Crop Rotation Strategies were studied in 1994 and 1995 in relation to growth and yield of irrigated processing tomatoes (Lycopersicum esculentum Mill.) The four treatments were three four-year rotation systems [conventional( conv-4), low input and organic] and a two-year rotation system [conventional (conv-2)]. The 4-year rotation was tomato-safflower-corn-wheat (or oats+vetch)/beans, and the 2-year rotation was tomato-wheat. Purple vetch (Vicia Sativa L.) was grown as a green manure cover crop preceeding tomatoes in the low input and organic systems. Nitrogen was supplied as a fertilizer in the conventional systems, as vetch green manure plus fertilizer in the low input system, and as vetch green manure plus turkey manure in the organic system. Tomato cv. Brigade was direct-seeded in the conventional systems and transplanted to the field in the low input and organic systems. In both years the winter cover crop was composed of a mixture of vetch and volunteer oats with N contents of 2.2% in 1994 and 2.7% (low input) or 1.8% (organic) in 1995. In 1994 yields were higher in conventionally grown tomatoes because a virus in the nursery infected the transplants used in the low input and organic systems. In 1995 tomatoes grown with the conv-4 systems had similar yields, which were higher than those of tomatoes grown with the conv-2 and organic systems...


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.

Growers converting from conventional to low-input and organic farming systems must rely on organic sources for adequate soil fertility. At the Sustainable Agriculture Farming Systems (SAFS) project at UC Davis, we measured soil fertility and biological parameters in four farming systems. By the end of the first 4 years, pH and percent nitrogen were consistently higher in organic and low-input than conventional plots for all crops. Levels of organic matter, phosphorous and potassium were significantly higher in the organic than conventional 2-year plots. Microbial biomass levels were consistently higher in organic and low-input systems, while plant parasitic nematode numbers were consistently lower. Nitrogen deficiency appeared to be a problem in organic tomatoes during the transition period. More research is needed into the dynamics of soil nutrient availability in low-input systems. For instance, we may need to develop new methods of assessing soil fertility in organically fertilized systems.


Scow, K.M., 1996. Interrelationships Between Micorbial Dynamics and Carbon Flow in Agroecosystems. In: Jackson, L.E. (ed.) Ecology in Agriculture Ch. 11:367-403.



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.

Cover-crop nitrogen supply and weed management were the most important challenges facing low-input and organic farming systems when compared to conventional systems in the first 4 years of the Sustainable Agriculture Farming Systems project at UC Davis. Cover-crop timing and management, using appropriate equipment, were important for the success of transitional systems. The participation of local farmers ensured that optimal agricultural practices were used to manage all farming systems. Researchers regularly consulted grower-cooperators to determine "best farmer practices" of conventional, low-input and organic farming systems.


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. American Journal of Alternative Agriculture 9 (1 & 2): 64-71.

In 1989 a group of researchers, farmers and farm advisors initiated an interdisciplinary study of the transition from conventional to low-input and organic management of a 4-year, five-crop rotation. Crop yields initially varied among systems, but now appear to be approaching each other after a transition period that included the development of practices and equipment most appropriate for each system. Farming practices and crop production costs are carefully documented to compare the various systems' economic performance and biological risks. Supplying adequate N and managing weeds were challenges for the low-input and organic systems during the first rotation cycle, and experiments are being conducted on an 8-acre companion block to find solutions to these and other problems. Leading conventional and organic growers provide a much-needed farmer perspective on cropping practices and economic interpretations, because we try to provide "best farmer" management of each system. Research groups within the project are focusing on soil microbiology, economics, pest management, agronomy and cover crop management.

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