Organic Plots Research Articles

Long‐Term Study of Properties of a Xerofluvent of the Guadalquivir River Valley under Organic Fertilization

The long‐term effect of inorganic and organic fertilization in a vegetable crop rotation on soil chemical and biochemical properties was investigated in a trial in southern Spain. Two crops were grown in succession, potato (Solanum tuberosum L.) and a mixed‐cropped strawberry–onion (Fragaria vesca L.–Allium cepa L.). Total organic carbon (TOC), Kjeldahl‐N, bicarbonate‐extractable P (Olsen‐P), ammonium acetate extractable‐potassium (AAE‐K), microbial biomass carbon (Cmic), and enzyme activity (dehydrogenase, β‐glucosidase, protease, and alkaline phosphatase) were determined in soils in the seventh and eighth year of management comparison. The metabolic quotient (qCO2) and the Cmic to TOC ratio were also calculated. Organically fertilized soils showed significant increases in TOC and Kjeldahl‐N, available‐P, AAE‐K, microbial biomass C, and enzymatic activities compared with those found under inorganically fertilized soils. The qCO2 values were greater in inorganic than in organic fertilized plots indicating a lower microbial community respired at a greater rate in inorganic fertilized soils. The Cmic to TOC ratio in organic plots was lower than in inorganic plots indicating that microorganism in inorganically fertilized soils could have a better efficiency in the conversion of C sources to microbial biomass. Long‐term organic fertilization positively affected soil organic matter content, thus improving soil chemical and biological fertility under arid environmental conditions in southwest Spain. However precautions must be taken as excessive accumulation of some nutrients, particularly N and P, can arise from the long‐term use of compost.

Species composition and community structure of the rove beetles (Coleoptera: Staphylinidae) in an experimental vineyard under different vineyard management systems

Community structure (species richness, dominance, similarity, diversity and seasonal dynamics) of the rove beetles (Staphylinidae) was examined in an abandoned, a conventional and an organic vineyard management plot of an experimental vineyard in Hungary.During the survey, a total number of 493 specimens belonging to 33 species were collected by pitfall traps. The dominant species were Sphenoma togata, Xantholinus linearis and Pseudocypus penetrans that presented 76.66% of all staphylinids collected in the vineyard. All of the most common staphylinid species had only one generation per year and overwintered as adults.There were significant differences in species richness and abundance; both were the highest in the abandoned plot. The dissimilarity in species composition between the differently treated plots was also high. The diversity was the highest in organic, and the lowest in conventionally treated plot, while the abandoned one showed an intermediate value.

Role of organic and conventional field boundaries on boreal bumblebees and butterflies

This study examined how field boundary habitat quality and farming system (organic or conventional) affect species richness and abundance of diurnal lepidopterans and bumblebees in boreal agricultural landscapes. The results showed positive effects of field boundary area on lepidopteran diversity, as well as positive effects of nectar flower abundance on lepidopterans and bumblebee abundance. Organic farming did not show any significant effects on lepidopteran diversity. The results suggested that a successful conservation strategy for lepidopterans occurring in boreal agroecosystems depend on proper management of field boundaries, irrespective of farming regime. As bumblebee diversity tended to be higher at organic plots it is concluded that these important pollinators might be able to react on even small changes in habitat quality of cultivated lands. The results concord with a general hypothesis that effects of organic farming might be overpowered by effects of landscape structure in heterogeneous landscapes.

Ten-Year Comparison of the Influence of Organic and Conventional Crop Management Practices on the Content of Flavonoids in Tomatoes

Understanding how environment, crop management, and other factors, particularly soil fertility, influence the composition and quality of food crops is necessary for the production of high-quality nutritious foods. The flavonoid aglycones quercetin and kaempferol were measured in dried tomato samples (Lycopersicon esculentum L. cv. Halley 3155) that had been archived over the period from 1994 to 2004 from the Long-Term Research on Agricultural Systems project (LTRAS) at the University of California-Davis, which began in 1993. Conventional and organic processing tomato production systems are part of the set of systems compared at LTRAS. Comparisons of analyses of archived samples from conventional and organic production systems demonstrated statistically higher levels (P < 0.05) of quercetin and kaempferol aglycones in organic tomatoes. Ten-year mean levels of quercetin and kaempferol in organic tomatoes [115.5 and 63.3 mg g(-1) of dry matter (DM)] were 79 and 97% higher than those in conventional tomatoes (64.6 and 32.06 mg g(-1) of DM), respectively. The levels of flavonoids increased over time in samples from organic treatments, whereas the levels of flavonoids did not vary significantly in conventional treatments. This increase corresponds not only with increasing amounts of soil organic matter accumulating in organic plots but also with reduced manure application rates once soils in the organic systems had reached equilibrium levels of organic matter. Well-quantified changes in tomato nutrients over years in organic farming systems have not been reported previously.

Yield, Boll Distribution and Fibre Quality of Hybrid Cotton (Gossypium hirsutum L.) as influenced by Organic and Modern Methods of Cultivation

AbstractIndia is the largest cotton‐growing country (8.9 million hectares) in the world and most of the area is rain‐dependent. Large amount of pesticides are used for the control of sucking pests and lepidopterans. Increasing demand for clean organic fibre has led to an interest in organic cotton. However, information on the effects of organic cultivation on fibre quality is limited. Seed cotton yield and fibre quality (length, strength, micronaire and uniformity) were determined for an organic and modern method of cultivation during 3 years (2002–2003 to 2004–2005) of a 11‐year (1994–1995 to 2004–2005) study. Vertical and horizontal distribution of bolls on a cotton plant was also determined in 2003–2004 and 2004–2005. At the end of year 11, soil samples were collected and analysed for soil organic carbon content, water‐stable aggregates (%), and mean weight diameter. Averaged over 3 years, an additional 94 kg seed cotton ha−1 was produced in the organic over the modern method of cultivation and the difference was significant. The year × treatment interaction was significant. Seed cotton yield in the organic plots was significantly greater than the modern method of cultivation plots in 2003–2004 because of a well‐distributed normal rainfall and low pest incidence. The main stem nodes 13–22 accounted for the largest numbers of bolls present on the plant. Plants of the organic plots had significantly (37–71 %) more bolls on nodes 13–27 than those for the plants of the modern method of cultivation. Lateral distribution of bolls on a sympodial (fruiting) branch, was noticed up to fruiting point 11. However, treatment differences were not significant. With regard to fibre quality (length, strength, fineness and uniformity), differences between years were significant. Inferior quality fibre was produced in 2004–2005 because of delayed planting and early cessation of rain. On average, cotton grown under organic conditions compared with the modern method of cultivation had significantly better fibre length (25.1 vs. 24.0 mm) and strength (18.8 vs. 17.9 g tex−1). Soil samples of the organic plots had significantly greater C content, water‐stable aggregates and mean weight diameter than the modern method of cultivation plots. Differences were restricted to the top layers (0–0.1 and 0.1–0.2 m). Yield benefits of growing cotton in an organic system over the modern method of cultivation are expected to be greater in years receiving normal rainfall and having low pest incidence.

Fertilizer Source and High Tunnel Production Environment Affect Antioxidant Levels of Pac Choi

An experiment was conducted at Olathe, Kan., in Spring 2004 to investigate the influence of organic and conventional fertilizer sources and application rates on antioxidant levels of pac choi (Brassica rapa L. cv. Mei Qing) in open fields and poly-covered high-tunnel plots. Organic plots received pre-plant application of composted cattle manure and alfalfa (Hu-More 1–1–1) at 0 kg/ha N, 156 kg/ha N, or 314 kg/ha N, and conventional plots received preplant application of 13N–13P–13K at 0 kg/ha N, 78 kg/ha N, or 156 kg/ha N. Antioxidant levels were measured using the oxygen radical absorbance capacity (ORAC) assay. There were significant effects of fertilizer source and high-tunnel environment on the antioxidant capacity of pac choi. Organic fertilization significantly increased hydrophilic ORAC of pac choi in open field plots, but not in high tunnels. Regardless of the fertilizer source, pac choi grown in the open field had significantly higher hydrophilic ORAC than that grown in tunnels. Lipophilic ORAC was significantly increased by organic fertilization but was not affected by high-tunnel production. Total ORAC (hydrophilic + lipophilic) was significantly higher in pac choi from organic or open-field plots, compared to conventional and high-tunnel plots, respectively. Although fertilizer rate did not show significant impact on antioxidant level of pac choi, hydrophilic and total ORAC seemed to decrease as the fertilizer rate increased, especially under conventional fertilization, while lipophilic ORAC reached the highest level at the medium fertilizer rate. Differences in antioxidant levels were likely associated with the enhanced phytochemical content of pac choi from organically fertilized and open-field plots.

Reduced nitrate leaching and enhanced denitrifier activity and efficiency in organically fertilized soils

Conventional agriculture has improved in crop yield but at large costs to the environment, particularly off-site pollution from mineral N fertilizers. In response to environmental concerns, organic agriculture has become an increasingly popular option. One component of organic agriculture that remains in question is whether it can reduce agricultural N losses to groundwater and the atmosphere relative to conventional agriculture. Here we report reduced N pollution from organic and integrated farming systems compared with a conventional farming system. We evaluated differences in denitrification potential and a suite of other soil biological and chemical properties in soil samples taken from organic, integrated, and conventional treatments in an experimental apple orchard. Organically farmed soils exhibited higher potential denitrification rates, greater denitrification efficiency, higher organic matter, and greater microbial activity than conventionally farmed soils. The observed differences in denitrifier function were then assessed under field conditions after fertilization. N(2)O emissions were not significantly different among treatments; however, N(2) emissions were highest in organic plots. Annual nitrate leaching was 4.4-5.6 times higher in conventional plots than in organic plots, with the integrated plots in between. This study demonstrates that organic and integrated fertilization practices support more active and efficient denitrifier communities, shift the balance of N(2) emissions and nitrate losses, and reduce environmentally damaging nitrate losses. Although this study specifically examines a perennial orchard system, the ecological and biogeochemical processes we evaluated are present in all agroecosystems, and the reductions in nitrate loss in this study could also be achievable in other cropping systems.

Phytochemical phenolics in organically grown vegetables.

Fruit and vegetable intake is inversely correlated with risks for several chronic diseases in humans. Phytochemicals, and in particular, phenolic compounds, present in plant foods may be partly responsible for these health benefits through a variety of mechanisms. Since environmental factors play a role in a plant's production of secondary metabolites, it was hypothesized that an organic agricultural production system would increase phenolic levels. Cultivars of leaf lettuce, collards, and pac choi were grown either on organically certified plots or on adjacent conventional plots. Nine prominent phenolic agents were quantified by HPLC, including phenolic acids (e. g. caffeic acid and gallic acid) and aglycone or glycoside flavonoids (e. g. apigenin, kaempferol, luteolin, and quercetin). Statistically, we did not find significant higher levels of phenolic agents in lettuce and collard samples grown organically. The total phenolic content of organic pac choi samples as measured by the Folin-Ciocalteu assay, however, was significantly higher than conventional samples (p < 0.01), and seemed to be associated with a greater attack the plants in organic plots by flea beetles. These results indicated that although organic production method alone did not enhance biosynthesis of phytochemicals in lettuce and collards, the organic system provided an increased opportunity for insect attack, resulting in a higher level of total phenolic agents in pac choi.

Integrated Use of Organic Manure and Chemical Fertilizer on Growth, Yield, and Quality of Sugarcane in High Ganges River Floodplain Soils of Bangladesh

A study was undertaken to evaluate the effects of integrated use of organic wastes such as press mud, farmyard manure (FYM), and green manure (Crotalaria juncea) along with chemical fertilizer on the yield and quality of sugarcane in High Ganges River Floodplain soils of Bangladesh. Chlorophyll a and Chlorophyll b contents of cane leave tissues were slightly increased by organic manure and green manure. Leaf area index (LAI) and total dry matter (TDM) production were higher during rapid grand growth phase. Application of fertilizer (based on soil test value) accompanied with FYM at 15 t ha−1 produced the maximum plant population density of 163.4×103 ha−1 and resulted in the highest cane and sugar yields of 108.4 and 9.47 t ha−1, respectively. The phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), iron (Fe), zinc (Zn), and manganese (Mn) contents in leaves were higher in organic manured plots over chemical fertilizer. The organic matter, total nitrogen (N), available P, K, and sulphur (S) contents of the soil increased slightly due to use of organic manure. It appeared that 25% reduction of fertilizer application is possible if FYM or press mud at 15 t ha−1 is used in successful sugarcane production.

Response of soil mites to organic cultivation in an ultisol in southeast Brazil

Soil-dwelling mites of four plots under organic management were investigated in April and December 1998 and in December 1999. Their populations were compared with mite populations in a pasture and forest in the vicinity. It was observed that there was always an initial reduction in the populations of soil mites and in the activity of the epigeic forms whenever a plot was opened up and disturbed mechanically in preparation for cultivation, irrespective of previous organic inputs. With time, the densities and activities of mites recovered under organic management. The uropodine and oribatid mites in particular benefited more from organic management than gamasine and actinedid mites. Uropodine mites increased tremendously under banana where there was fresh cow dung manure. Oribatid mite species Nothrus seropedicalensis and Archegozetes magnus were dominant in organic plots where the soil was moist and temperatures were lower than the ambient. Protoribates rioensis was dominant in organic plots where the soil was drier and temperatures were higher than the ambient. Galumna was the most active oribatid taxon on the floor of all plots, with the highest activity recorded under maracuja and in pasture plots. The results suggest that while densities and activities of soil mites increased in the organic plots, the community structure and recruitment period of oribatid mites were altered. Oribatid mite diversity was higher in the organic plots than in the pasture but lower than in the forest, where Belba sp. and many Eremobelboid brachypiline genera were present, but absent in the organic plots and pasture.

Response of soil mites to organic cultivation in an ultisol in southeast Brazil

Soil-dwelling mites of four plots under organic management were investigated in April and December 1998 and in December 1999. Their populations were compared with mite populations in a pasture and forest in the vicinity. It was observed that there was always an initial reduction in the populations of soil mites and in the activity of the epigeic forms whenever a plot was opened up and disturbed mechanically in preparation for cultivation, irrespective of previous organic inputs. With time, the densities and activities of mites recovered under organic management. The uropodine and oribatid mites in particular benefited more from organic management than gamasine and actinedid mites. Uropodine mites increased tremendously under banana where there was fresh cow dung manure. Oribatid mite species Nothrus seropedicalensis and Archegozetes magnus were dominant in organic plots where the soil was moist and temperatures were lower than the ambient. Protoribates rioensis was dominant in organic plots where the soil was drier and temperatures were higher than the ambient. Galumna was the most active oribatid taxon on the floor of all plots, with the highest activity recorded under maracuja and in pasture plots. The results suggest that while densities and activities of soil mites increased in the organic plots, the community structure and recruitment period of oribatid mites were altered. Oribatid mite diversity was higher in the organic plots than in the pasture but lower than in the forest, where Belba sp. and many Eremobelboid brachypiline genera were present, but absent in the organic plots and pasture.

Total Phenolic and Flavonoid Contents of Organically and Conventionally Grown Lettuce, Collards and Chinese Cabbage

Organic vegetables have been suggested to produce higher levels of phytochmemicals, which play active roles in disease prevention. We measured total phenolic and aglycone flavonoid (apigenin, kaempferol, luteolin, and quercetin) contents in leaves of organically- and conventionally-grown lettuce (`Kalura' and `Red Sails'), collards (`Top Bunch') and Pak Choi (`Mei Qing') greens during spring and summer trials, using the Folin assay and HPLC, respectively. Postharvest changes in phenolic contents of organic and conventional lettuce were also investigated after 17-day storage at 4 °C. Production system did not cause a significant difference in total phenolic levels of lettuce and collards in either trial, but total phenolics were significantly higher in organic Pak Choi in the summer trial, possibly due to greater flea beetle damage in the organic plots. Organic production did not affect the aglycone flavonoid levels of lettuce and collards in the spring trial except that apigenin increased in organic samples. In the summer trial, however, concentrations of kaempferol, luteolin and quercetin tended to increase in organic lettuce and collards; only luteolin showed promising increase in Pak Choi. Species and cultivars both had significant effects on total phenolic and flavonoid contents. After 17-day storage, total phenolic content significantly increased in both organic and conventional lettuce although the concentrations of aglycone flavonoids remained relatively constant. Total phenolic content was higher in organic `Red Sails' at a marginal significance level after storage, while it did not differ between organic and conventional `Kalura'. We noted a dominant presence of glycoside flavonoids in lettuce before and after storage, which warrants further study.

Yield increases during the organic transition: improving soil quality or increasing experience?

Reported increases in crop yields over the first few years of organic farming (especially during the 3-year “transitional” period established in US law) have been attributed to gradual improvements in soil properties, such as the capacity of the soil microbial community to mineralize N or to suppress disease. To test the hypothesis that yield increases with years of organic farming are due to improvements in soil properties, we compared identically managed organic and transitional plots differing only in duration of organic management (>5 versus <1 year). Conventional plots were included for reference purposes. There was no difference in tomato ( Lycopersicon esculentum Mill.) growth or yield between established organic and first-year transitional plots, but both outperformed the comparable conventional system. Even no-compost subplots within the transitional plots had yields similar to established organic plots, so the yield advantage relative to conventional plots was apparently due to beneficial effects of a winter legume cover crop in a wet year. Soil inorganic N did not differ between transitional and organic plots. Conventional and organic plots differed in soil microbial community composition, but transitional plots were not intermediate between conventional and organic. In the second year of the organic transition, when maize ( Zea mays L.) was grown, yields were again not significantly different from the established organic system. This result is inconsistent with the hypothesis that yield-limiting differences in soil quality between organic and conventional systems take at least 3 years to develop. An alternative hypothesis, not tested directly, is that previously reported yield increases result from improved management with increasing experience, not improving soil quality.

Effect of organic matter application on N2O, NO, and NO2 fluxes from an Andisol field

We used an automated flux monitoring system to measure N2O, NO, and NO2 fluxes from an Andisol field between May 1999 and September 2000. Pac choi and spinach were cultivated for 1.5 months in 1999 and 2000, respectively. We applied 15 g N m−2 of oilcake, cattle manure, fishmeal, dried cattle excreta, or urea to each plot. N2O and NO emissions from organic plots over the cultivation period were 2.55 mg N m−2 to 35.2 mg N m−2, and 2.48 mg N m−2 to 22.5 mg N m−2, respectively. Those from the urea plot were 10.9 mg N m−2 to 21.1 mg N m−2, and 52.0 mg N m−2 to 105 mg N m−2, respectively. We estimated that N2O emission from organic fertilizer is equivalent to that from chemical fertilizer application on Japanese Andisol field.

The performance of organic and conventional cropping systems in an extreme climate year

AbstractThe 1999 severe crop season drought in the northeastern US was followed by hurricane-driven torrential rains in September, offering a unique opportunity to observe how managed and natural systems respond to climate-related stress. The Rodale Institute Farming Systems Trial has been operating since 1981 and consists of three replicated cropping systems, one organic manure based (MNR), one organic legume based (LEG) and a conventional system (CNV). The MNR system consists of a 5-year maize–soybean–wheat–clover/hay rotation, the LEG of a 3-year maize–soybean–wheat–green manure, and the CNV of a 5-year maize-soybean rotation. Subsoil lysimeters allowed quantification of percolated water in each system. Average maize and soybean yields were similar in all three systems over the post-transition years (1985–1998). Five drought years occurred between 1984 and 1998 and in four of them the organic maize outyielded the CNV by significant margins. In 1999 all crop systems suffered severe yield depressions; however, there were substantial yield differences between systems. Organic maize yielded 38% and 137% relative to CNV in the LEG and MNR treatments, respectively, and 196% and 152% relative to CNV in the soybean plots. The primary mechanism of the higher yield of the MNR and LEG is proposed to be the higher water-holding capacity of the soils in those treatments, while the lower yield of the LEG maize was due to weed competition in that particular year and treatment. Soils in the organic plots captured more water and retained more of it in the crop root zone than in the CNV treatment. Water capture in the organic plots was approximately 100% higher than in CNV plots during September's torrential rains.

Soil organisms in organic and conventional cropping systems

Despite the recent interest in organic agriculture, little research has been carried out in this area. Thus, the objective of this study was to compare, in a dystrophic Ultisol, the effects of organic and conventional agricultures on soil organism populations, for the tomato (Lycopersicum esculentum) and corn (Zea mays) crops. In general, it was found that fungus, bacterium and actinomycet populations counted by the number of colonies in the media, were similar for the two cropping systems. CO2 evolution during the cropping season was higher, up to the double for the organic agriculture system as compared to the conventional. The number of earthworms was about ten times higher in the organic system. There was no difference in the decomposition rate of organic matter of the two systems. In general, the number of microartropods was always higher in the organic plots in relation to the conventional ones, reflectining on the Shannon index diversity. The higher insect population belonged to the Collembola order, and in the case of mites, to the superfamily Oribatuloidea. Individuals of the groups Aranae, Chilopoda, Dyplopoda, Pauropoda, Protura and Symphyla were occasionally collected in similar number in both cropping systems.

Effect of Compost Amendments on Disease Severity and Yield of Tomato in Conventional and Organic Production Systems.

Field trials were conducted over 2 years to assess the effects of compost amendments on disease development in organic and conventional processing tomato (Lycopersicon esculentum L.) production systems. The incidence of anthracnose fruit rot was reduced in organic tomato plots amended with a high rate of composted cannery wastes compared with the incidence in nonamended control plots in 1998 when disease incidence was high. Marketable yield was increased by 33% in compost-amended organic plots. Plots amended with a high compost rate had more ripe fruit than the nonamended control. The incidence of anthracnose and of total disease on fruit was less on the cultivar OH 8245 than on Peto 696. Total fruit yield of OH 8245 but not Peto 696 in organic plots was increased by amendment with composted cannery wastes. In conventional tomato production, composted yard wastes increased disease severity on foliage both years but reduced bacterial spot incidence on fruit in 1997, when disease pressure was high. The incidence of anthracnose was not affected by composted yard wastes. Marketable and total fruit yields of Peto 696 were not increased in compost-amended conventional plots. The plant activator Actigard reduced foliar disease severity and the incidence of bacterial spot and anthracnose on fruit, while increasing yield of marketable fruit.

Impact of Strawberry Cultivar and Incidence of Pests on Yield and Profitability of Strawberries under Conventional and Organic Management Systems

ABSTRACT Yield, incidence of pests, and profitability of strawberries under conventional and organic management systems were measured through four fruiting seasons, using three cultivare widely grown in the northeastern United States (dayneutrals [Tribute or Tristar], Earliglow and Honeoye). Fruits were more abundant in conventional than in organic plots, but the average weight of fruit was not affected by management system. Of all strawberry cultivare tested in this study, Honeoye was the most productive, both in terms of number and weight of harvested fruits. Incidence of tarnished plant bug damage by was much higher than for grey mould or slugs. Density of nymphs and proportion of fruits damaged by plant bugs were higher in organic than in conventional plots, and for Honeoye than dayneutrals or Earliglow. In contrast, management system and strawberry cultivar did not affect to a great extent the incidence of damage by grey mould or slugs. Productivity of strawberry plants was negatively correlated with incidence of damage by plant bugs, and positively with incidence of grey mould. Weed biomass was greater in organic than in conventional plots. Economic analysis indicated that a lack of reliable, effective measures for managing pests of strawberries without synthetic pesticides, especially weeds and plant bugs, may severely constrain yield and profitability of organic strawberries in the northeastern United States. Due to its high productivity and low susceptibility to plant bugs, Honeoye was by far the most profitable cultivar in this study, and appeared highly suitable for organic management.

Nematode-trapping fungi in conventionally and organically managed corn-tomato rotations

We tested the hypothesis that nematode-trapping fungi would be more abundant in organically-managed than in conventionally-managed plots (corn-tomato rotation) in the Long Term Research on Agriculture Systems Project (Yolo County, CA). The replicated plots were established in 1992, began receiving different levels of organic matter (no organic amendments or incorporation of a winter legume crop plus composted manure) in 1993, and were sampled for fungi four times, twice near harvest (Sep 1995 and Nov 1996) and twice near planting (May 1996 and 1997). Fungi were quantified using soil dilution and soil sprinkle plates combined with most probable number procedures. The following fungi were detected: Arthrobotrys haplotyla, A. oligospora, A. thaumasia, Dactylella leptospora, Harposporium anguillulae, Meristacrum sp., Monacrosporium eudermatum, Nematoctonus leiosporus, and Stylopage sp. Arthrobotrys thaumasia was the most abundant (about 10 propagules/g of soil) followed by A. oligospora (about 1 propagule/g of soil). Population densities of the other fungi were usually less than 1 propagule/g of soil. Except for N. leisporus, which was detected more frequently in the organic plots, and Meristacrum sp., which was more abundant in the organic plots, detection frequencies and population densities of nematode-trapping fungi were similar in conventional and organic plots.

641 Preliminary Evaluation of Organic Desert Vegetable Production Systems

Experiments were conducted during 1998–99 seasons to evaluate the potential for organic vegetable production in the low desert of the southwestern United States. The experimental design included three summer management options [fallow, cowpea (Vigna sinensis), and sudangrass (Sorghum vulgare)] in factorial combination with alternative production systems, which included organic and conventional systems. The crops cultivated were iceberg lettuce (Lactuca sativa L) during the fall–winter period and melons (Cucumis melo Reticulatus Group) during the spring. The organic plots were managed with strict adherence to California Certified Organic Farmers (CCOF) guidelines. Summer cover crop management seemed to influence the early growth and N uptake of lettuce, but had no final effect on yield and quality. The organic production system resulted in lower yields and inferior product quality compared to the conventional system. Generally, disease and weeds were not limiting factors, although labor costs for weed control would be slightly higher in organic plots. Insects, primarily aphids (various types) and thrips (Frankliniella Occidentalis Perancle), and fertility, primarily N, were factors limiting yield and quality in organic systems. Control of whiteflies (Bemisia argentifoli) was the limiting factor for melons. Studies during 1999–2000 are focused on overcoming the challenges of the insect and fertility management in organic systems.