Meteorological fluctuations define long-term crop yield patterns in conventional and organic production systems.

Variability in meteorological patterns presents significant challenges to crop production consistency and yield stability. Meteorological influences on corn and soybean grain yields were analyzed over an 18-year period at a long-term experiment in Beltsville, Maryland, U.S.A., comparing conventional and organic management systems. Precipitation and temperature variables explained much of the yield variability, with precipitation and heat stress during the late vegetative and early reproductive phases of crop growth accounting for the majority of yield variability in all crops and management systems. Crop yields under conventional and organic management followed similar periodic patterns, but yields were 31% and 20% lower in organic than conventional corn and soybean, respectively. The efficiency of grain yield per unit precipitation was higher under conventional than organic management, highlighting the importance of crop management for optimizing production in response to meteorological variability. Periodic yield and precipitation patterns did not consistently align with global meteorological cycles such as the El Niño Southern Oscillation.

Fruit metabolite networks in engineered and non-engineered tomato genotypes reveal fluidity in a hormone and agroecosystem specific manner.

INTRODUCTION: Metabolomics provides a view of endogenous metabolic patterns not only during plant growth, development and senescence but also in response to genetic events, environment and disease. The effects of the field environment on plant hormone-specific metabolite profiles are largely unknown. Few studies have analyzed useful phenotypes generated by introducing single or multiple gene events alongside the non-engineered wild type control at field scale to determine the robustness of the genetic trait and its modulation in the metabolome as a function of specific agroecosystem environments. OBJECTIVES: We evaluated the influence of genetic background (high polyamine lines; low methyl jasmonate line; low ethylene line; and isogenic genotypes carrying double transgenic events) and environments (hairy vetch, rye, plastic black mulch and bare soil mulching systems) on the metabolomic profile of isogenic reverse genetic mutations and selected mulch based cropping systems in tomato fruit. Net photosynthesis and fruit yield were also determined. METHODS: NMR spectroscopy was used for quantifying metabolites that are central to primary metabolism. We analyzed both the first moment (means) of metabolic response to genotypes and agroecosystems by traditional univariate/multivariate methods, and the second moment (covariances) of responses by creating networks that depicted changes in correlations of paired metabolites. This particular approach is novel and was necessary because our experimental material yielded highly variable metabolic responses that could not be easily understood using the traditional analytical approaches for first moment statistics. RESULTS: High endogenous spermidine and spermine content exhibited strong effects on amino acids, Krebs cycle intermediates and energy molecules (ADP + ATP) in ripening fruits of plants grown under different agroecosystem environments. The metabolic response to high polyamine genotypes was similar to the response to hairy vetch cover crop mulch; supported by the pattern of changes in correlation between metabolites. Changes in primary metabolites of genotypes mutated for the deficiency of ethylene or methyl jasmonate were unique under all growth conditions and opposite of high polyamine genotype results. The high polyamine trait was found to dominate the low ethylene and low jasmonate mutations under field conditions. For several metabolites low ethylene and low methyl jasmonate genotypes had an inverse relationship. Collectively, these results affirm that interactions between metabolite pathways and growth environments are affected by genotype, and influence the metabolite quality of a crop. CONCLUSION: This study portrays how metabolite relationships change, both in mean and in correlation, under different genotypic and environmental conditions. Although these networks are surprisingly dynamic, we also find examples of selectively conserved associations.

Concentrations and allelopathic effects of benzoxazinoid compounds in soil treated with rye (Secale cereale) cover crop.

The concentration of benzoxazinoids (BX) was measured in field soils at selected intervals after rye residue was either incorporated or left on the soil surface. The spectrum of compounds arising in the soil persisted approximately two weeks and was dominated by methoxy containing BX compounds, which were only minor components of the rye foliage. Growth assays with lettuce and smooth pigweed species showed inhibition when treated soils were tested during the first two weeks after rye applications; however, there were no sufficient concentrations of any one BX compound in the soil to explain these affects. Solution applications of two pure BX compounds, benzoxazolin-2(3H)-one (BOA) and 6-methoxy-benzoxazolin-2(3H)-one (MBOA), to the surface of soils revealed that movement into the soil column was minimal (greater than 70% BOA and 97% MBOA remained in the top 1-cm of soil profiles) and that the time course for their complete dissipation was less than 24 h.

Tomato response to legume cover crop and nitrogen: differing enhancement patterns of fruit yield, photosynthesis and gene expression.

Excessive use of nitrogen (N) in crop production has impacted ecosystems by contaminating soil and water. Management of N in agriculture is therefore of global concern. Sustainable agriculture systems that use leguminous cover crops such as hairy vetch (Vicia villosa Roth) to fix N and enrich soil organic matter by fixing carbon provide an alternative strategy. N signalling pathways were found associated with delayed leaf senescence and disease tolerance of hairy vetch-grown tomatoes. To test whether N in hairy vetch is the only contributing factor leading to these phenotypes, we designed a pot experiment in the field to analyse growth and gene expression in tomatoes, one set with soil overwintered without a cover crop (bare soil) and the other with soil overwintered with a hairy vetch cover crop including the vetch residue on the soil surface. Additionally, supplementary N fertiliser was also provided to aid distinguishing tomato responses to vetch from those to inorganic N. Tomato fruit yield, plant biomass and photosynthesis were higher in plants grown in vetch than bare soil. Tomato growth and photosynthesis metrics exhibited a parabolic response to inorganic N in bare soil, suggesting the potential for N toxicity in pots with the highest N rate. Vetch-grown tomato plants mitigated these effects and maintained elevated photosynthetic rates at high inorganic N levels. Vetch-grown plants also mitigated a decline in expression of several genes regulating nitrogen and carbon metabolism and upregulated the defence-related gene, osmotin, relative to plants grown in bare soil. Thus, some of the positive responses of tomatoes to a hairy vetch cover crop observed in the field seem mediated by physiological cues other than the additional N provided by the vetch cover crop.

Evaluation of vegetable production management practices to reduce the ecological risk of pesticides.

The ability of agricultural management practices to reduce the ecological risks of pesticides was evaluated. Risk quotients, a mathematical description of the relationship between exposure and toxicity, and hazard ratings, a rank of the potential risk of pesticides to aquatic environments, were calculated for conventional and alternative cultivation practices for tomatoes: Poly-Bare, raised beds covered with polyethylene mulch with bare-soil furrows; Poly-Rye, raised beds covered with polyethylene mulch with cereal rye (Secale cereale) grown in the furrows; and Vetch, raised beds and furrows planted with hairy vetch seed (Vicia villosa). Evaluations were conducted using measured pesticide concentrations in runoff at the edge-of-field and estimated environmental concentrations in an adjacent creek and a theoretical pond receiving the runoff. Runoff from Poly-Bare presented the greatest risk to ecosystem health and to sensitive organisms, whereas the use of Vetch minimized these risks. Previous studies have shown that harvest yields were maintained and that runoff volume, soil loss, and off-site transport of pesticides measured in runoff were reduced using the alternative management practices (Poly-Rye and Vetch). Together, these results indicate that the alternative management practices (Poly-Rye and Vetch) have a less adverse impact on the environment than the conventional management practice (Poly-Bare) while providing growers with an acceptable economic return. In addition, the present study demonstrates the need to consider the management practice when assessing the potential risks and hazards for certain pesticides.

Reducing insecticide and fungicide loads in runoff from plastic mulch with vegetative-covered furrows.

A common management practice for the production of fresh-market vegetables utilizes polyethylene (plastic) mulch because it increases soil temperature, decreases weed pressure, maintains soil moisture, and minimizes soil contact with the product. However, rain events afford much more erosion and runoff because 50-75% of the field is covered with an impervious surface. A plot study was conducted to compare and to quantify the off-site movement of soil, insecticides, and fungicides associated with runoff from plots planted with Sunbeam tomatoes (Lycopersicon esculentum Mill) using the conventional polyethylene mulch management practice vs an alternative management practice-polyethylene mulch-covered beds with cereal rye (Secale cereale) planted in the furrows between the beds. The use of cereal rye-covered furrows with the conventional polyethylene system decreased runoff volume by more than 40%, soil erosion by more than 80%, and pesticide loads by 48-74%. Results indicate that vegetative furrows are critical to minimizing the negative aspects of this management practice.

Hydroxamic acid content and toxicity of rye at selected growth stages.

Rye (Secale cereale L.) is an important cover crop that provides many benefits to cropping systems including weed and pest suppression resulting from allelopathic substances. Hydroxamic acids have been identified as allelopathic compounds in rye. This research was conducted to improve the methodology for quantifying hydroxamic acids and to determine the relationship between hydroxamic acid content and phytotoxicity of extracts of rye root and shoot tissue harvested at selected growth stages. Detection limits for an LC/MS-MS method for analysis of hydroxamic acids from crude aqueous extracts were better than have been reported previously. (2R)-2-beta-D-Glucopyranosyloxy-4-hydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA-G), 2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA), benzoxazolin-2(3H)-one (BOA), and the methoxy-substituted form of these compounds, (2R)-2-beta-D-glucopyranosyloxy-4-hydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA glucose), 2,4-hydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA), and 6-methoxy-benzoxazolin-2(3H)-one (MBOA), were all detected in rye tissue. DIBOA and BOA were prevalent in shoot tissue, whereas the methoxy-substituted compounds, DIMBOA glucose and MBOA, were prevalent in root tissue. Total hydroxamic acid concentration in rye tissue generally declined with age. Aqueous crude extracts of rye shoot tissue were more toxic than extracts of root tissue to lettuce (Lactuca sativa L.) and tomato (Lycopersicon esculentum Mill.) root length. Extracts of rye seedlings (Feekes growth stage 2) were most phytotoxic, but there was no pattern to the phytotoxicity of extracts of rye sampled at growth stages 4 to 10.5.4, and no correlation of hydroxamic acid content and phytotoxicity (I50 values). Analysis of dose-response model slope coefficients indicated a lack of parallelism among models for rye extracts from different growth stages, suggesting that phytotoxicity may be attributed to compounds with different modes of action at different stages. Hydroxamic acids may account for the phytoxicity of extracts derived from rye at early growth stages, but other compounds are probably responsible in later growth stages.

Use of vegetative furrows to mitigate copper loads and soil loss in runoff from polyethylene (plastic) mulch vegetable production systems.

The transport of runoff with high copper concentrations and sediment loads into adjacent surface waters can have adverse effects on nontarget organisms as a result of increased turbidity and degraded water quality. Runoff from vegetable production utilizing polyethylene mulch can contain up to 35% of applied copper, a widely used fungicide/bactericide that has adverse effects on aquatic organisms. Copper is primarily transported in runoff with suspended particulates; therefore, implementation of management practices that minimize soil erosion will reduce copper loads. Replacing bare-soil furrows with furrows planted in rye (Secale cereale) significantly improved the sustainability of vegetable production with polyethylene mulch and reduced the potential environmental impact of this management practice. Vegetative furrows decreased runoff volume by >40% and soil erosion by >80%. Copper loads with runoff were reduced by 72% in 2001, primarily as a result of reduced soil erosion since more than 88% of the total copper loads were transported in runoff with suspended soil particulates. Tomato yields in both years were similar between the polyethylene mulch plots containing either bare-soil or vegetative furrows. Replacing bare-soil furrows with vegetative furrows greatly reduces the effects of sediments and agrochemicals on sensitive ecosystems while maintaining crop yields.

Comparison of copper levels in runoff from fresh-market vegetable production using polyethylene mulch or a vegetative mulch.

Runoff from tomato (Lycopersicon esculentum Mill.) production with polyethylene mulch has been implicated in the failure of commercial shellfish farms in the Mid-Atlantic Region of the United States. Copper, applied in the form of copper hydroxide, is the most widely used fungicide-bactericide for control of tomato diseases and recently has been detected in the Chesapeake Bay (USA) watershed. Elevated levels of copper have been shown to have adverse effects on shellfish, finfish, and other aquatic organisms. This research evaluates the off-site movement of copper with the dissolved phase and the particulate phase of runoff from controlled field plots containing tomato plants grown in either polyethylene mulch or a vegetative mulch, hairy vetch (Vicia villosa Roth.). Overall, runoff collected from polyethylene mulch plots contained significantly (p < or = 0.05) greater loads of dissolved- and particulate-phase copper than runoff from hairy vetch mulch plots. However, the loss of copper associated with the particulate phase was significantly greater (p < or = 0.05) than that associated with the dissolved phase of runoff from both mulch treatments, with the particulate phase accounting for more than 80% of the copper loads. The reported toxicity of copper to aquatic organisms and the greater runoff volume, soil loss, and off-site loading of copper measured in runoff from the polyethylene mulch suggests that this management practice is less sustainable and may have a more harmful impact on aquatic ecosystems.

Foliar Disease in Fresh-Market Tomato Grown in Differing Bed Strategies and Fungicide Spray Programs.

A 3-year field study in central Maryland evaluated foliar disease in fresh-market tomato grown using combinations of four bed strategies and three fungicide programs. Bed strategies included uncovered beds with or without a composted dairy manure amendment or beds covered with black polyethylene or hairy vetch mulch. Fungicide programs included no fungicide, weekly fungicide, or fungicide applications scheduled according to the TOMCAST disease predictor. In plots with hairy vetch-covered beds, early blight caused by Alternaria solani, Septoria leaf spot caused by Septoria lycopersici, and defoliation were lower versus uncovered beds each year. Early blight and defoliation were lower in beds covered with vetch versus polyethylene mulch in 2 of 3 years. Disease severity, defoliation, and marketable yield were similar for the weekly and TOMCAST fungicide programs, with 40 to 50% fewer sprays using TOMCAST. Marketable yield was similar among bed strategies except for higher yields in covered versus uncovered and unamended beds in a relatively wet year and lower yields in vetch versus polyethylene beds in a dry year.

Factors Associated with Foliar Disease of Staked Fresh Market Tomatoes Grown Under Differing Bed Strategies.

The use of mulch or compost to reduce foliar disease in fresh market tomato could reduce fungicide use. Between 1997 and 1999, foliar disease was monitored in tomatoes grown in beds with bare soil, black polyethylene, composted dairy manure, or hairy vetch. Early blight was reduced in plots with vetch compared with bare soil or compost in all years and compared with polyethylene cover in 1 year. Early blight was reduced in plots with polyethylene versus compost and bare soil in 1 and 2 years, respectively. Septoria leaf spot was reduced in plots with vetch versus other bed strategies in 1998 and bare soil or compost in 1999. This disease was reduced in plots with polyethylene versus bare soil or compost in 1998 and 1999. Soil coverage of tomato leaflets and soil particle dispersal were reduced in plots with polyethylene or vetch versus bare soil or compost in both years that these variables were assessed. Sensor wetness duration was reduced in plots with polyethylene or vetch versus bare soil or compost in one of two years. These findings suggest that foliar disease reduction in mulch was associated with reduced splash dispersal and, in one year, reduced leaf wetness.