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Research is lacking on the impact of alternative reduced tillage (RT) systems on vegetable crop performance and soil quality, especially in organic production systems, where weed control cannot rely on synthetic herbicides. A 2-year field study was implemented in Aug. 2010 in Knoxville, TN, to evaluate cover crop–based systems for organic vegetable production either with or without spring tillage. Treatments, all organically managed, included 1) Till (+ACC), spring tillage of a winter cover crop with aboveground cover crop biomass (ACC) retained and soil covered by polyethylene mulch; 2) Till (−ACC), spring tillage of a winter cover crop with aboveground cover crop biomass (ACC) removed before tillage and soil covered by polyethylene mulch; and 3) RT system with no spring tillage and mechanically terminated winter cover crop residue on the soil surface. Vegetable crops of eggplant (Solanum melongena L.) and watermelon [Citrullus lanatus (Thunb.) Matsum. et Nakai] were planted in 2011 and 2012, respectively. Crop yield, cover crop biomass accumulation, soil N and C dynamics, and weed density were assessed. Marketable eggplant yield and marketable watermelon yield did not differ among treatments, but weed density was higher in the RT system. Measures of soil quality after 2 years of the study indicated that particulate organic matter-carbon (POM-C) and -nitrogen (POM-N) were highest in the RT treatment, a significant increase as compared with values at the beginning of the study. As a measure of the active fraction of soil organic matter, this indicates that the RT system may best maintain and improve soil quality in similar regional organic vegetable cropping systems. As indicated by measures of soil quality and crop yield, removal of aboveground cover crop biomass did not negatively impact the Till (−ACC) system as compared with the Till (+ACC).

Abstract

Seasonal changes in soluble carbohydrates of Fraser fir [Abies fraseri (Pursh) Poir.] needles were monitored in Fall 1984, Spring 1985, and Fall 1985 through Spring 1986. Raffinose concentration increased in the fall and decreased in the spring. There was a 23-fold increase in raffinose concentration from Aug. 1985 to Jan. 1986. Sucrose concentration varied from fall to spring with the lowest concentration occurring in February. Postharvest needle abscission from harvested branches held 6 weeks without water was inversely correlated with raffinose concentration at the time of harvest. Diurnal fluctuations in soluble carbohydrates were monitored on 12 July and 26 Oct. 1985. Raffinose concentration fluctuated slightly on both dates with a decrease during the dark period. On 12 July, sucrose increased during the day and decreased at night, whereas hexoses decreased in the day and increased at night. No significant diurnal changes in sucrose or hexose were evident on 26 Oct. Controlled-environment studies at 24° (day)/18°C (night), 18°/12°, and 12°/6° showed that most of the raffinose accumulation was due to low temperature; the remainder to short days. Postharvest needle loss was lowest in plants with high needle raffinose concentrations resulting from the 12°/6° temperature. Storage without water resulted in significant postharvest needle loss for shoots from plants preconditioned with 24°/18° and 18°/12°, but not for those exposed to 12°/76°. Compared to long days, plants preconditioned with short days lost fewer needles following harvest.

Anaerobic soil disinfestation (ASD) is a biologically based, non-fumigant, pre-plant soil treatment developed to control soilborne plant pathogens and plant-parasitic nematodes in specialty crop production systems. Soil treatment by ASD includes the incorporation of a labile carbon (C) source, tarping with plastic, and irrigation of the topsoil to saturation (5 cm irrigation) to create conditions conducive to anaerobic decomposition of the added C source. A field study was implemented beginning in Fall 2010 and repeated in the same plot locations in Fall 2011 in Knoxville, TN, to evaluate ASD. Soil properties, weed and Rhizoctonia solani population dynamics, and crop performance were evaluated after ASD treatment with several potential C sources for ASD before production of fresh-market tomato (Solanum lycopersicum L. ‘Red Defender’) and red bell pepper (Capsicum annum L. ‘Red Knight X3R’). Treatments included: 1) untreated control; 2) mustard seed meal (biofumigant control); 3) ASD with dried molasses; 4) ASD with soil-incorporated Indian mustard (Brassica juncea L.), white mustard (Sinapis alba L.), and arugula (Eruca sativa Mill.) cover crop with molasses added at cover crop incorporation; 5) ASD with soil-incorporated Indian mustard, white mustard, and arugula cover crop; 6) ASD with soil-incorporated cereal rye (Secale cereale L.) cover crop with molasses added at cover crop incorporation; and 7) ASD with soil-incorporated cereal rye cover crop. Accumulated soil anaerobic conditions were significantly greater than the untreated control in all ASD treatments except the ASD mustard/arugula treatment. Although not related to accumulated anaerobic conditions, populations of R. solani were lowest and equivalent to the biofumigant control for ASD cereal rye and ASD mustard/arugula treatments. Differences in weed populations and soil inorganic nitrogen among treatments were limited. Yield of bell pepper and tomato did not differ among treatments, which may have been partly the result of the low pest pressure observed at the site over the 2 years of the study.