Carbon and Nitrogen Mineralization and Persistence of Organic Residues under Conservation and Conventional Tillage

Abstract

A combination of high biomass cover crops with organic mulches may be an option for no‐till vegetable production, but information on mineralization rates from these residues is lacking. The objective of this study was to assess nutrient release rates and persistence from mimosa (Albizia julibrissin Durazz.), lespedeza [Lespedeza cuneata (Dum. Cours.) G. Don], oat (Avena sativa L.) straw, and soybean [Glycine max (L.) Merr.] residues under conventional and conservation tillage. The experiment was conducted in Tallassee, AL using litterbag methodology in a split‐plot design (main plots: two tillage systems; subplots: four residue types). Comparison of rate constants showed that labile portions of residues was more affected by tillage than recalcitrant portions. In spring, mimosa residue contained 78 kg N ha−1 when buried the previous fall, compared to 123 kg N ha−1 when surface placed; soybean residue showed similar results (39 vs. 72 kg N ha−1, respectively). Results were similar for lespedeza (72 vs. 101 kg N ha−1, respectively), but not for oat straw (24 vs. 26 kg N ha−1, respectively). After 1 yr, surface placed mimosa residue mineralized 33% of initial N compared to 71% when buried, while surface placed lespedeza mineralized 36% of initial N compared to 64% when buried. Soybean residue mineralized N quickly regardless of placement (73 vs. 87%, respectively). This study demonstrates that cut‐and‐carry mulches may be used under conservation tillage for the enhancement of soil organic matter (SOM), soil organic carbon (SOC), and soil N status.