Conservation Tillage Effects On Carbon, Nitrogen and Mass Loss From Organic Residues.

Traditional organic vegetable production relies on tillage for weed control, but organic producers may adopt no-till if sufficient weed suppression can be achieved. A combination of high biomass cover crops with organic mulches may provide vegetable producers with multiple benefits, but information on nutrient release from these residues is lacking. Information on the timely release of nutrients from organic residues will help producers make informed decisions regarding residue management, including adoption of conservation or conventional tillage. The objective of this study was to assess carbon (C) and nitrogen (N) release and mass loss rates from organic residues (mimosa, lespedeza, straw, and soybean) under conventional and conservation tillage. The experiment used litterbag methodology and consisted of a split plot design with tillage (2) as main plots and mulch types (4) as subplots with four replicates in central eastern Alabama. Carbon and N release rates are presented with residue persistence.  Data were fitted to double exponential decay models which served as the basis for comparison between conservation and conventional tillage.  The labile portions of buried residues are more susceptible to decomposition than surface residues.  Mimosa sequesters 518 kg ha^-1 more C and 52 kg ha^-1 more N under conservation tillage than conventional tillage after one year, with 45 kg N ha^-1 more N potentially available at spring planting on May 1.  More nutrients are potentially available to succeeding crops from surface residues, which act as a slow release fertilizer, compared to incorporated residues.  This study demonstrates that in situ cover crops and mulches may be utilized under conservation tillage for the enhancement of soil organic matter and soil nutrient status.