Decomposition of crop residues under conventional and zero tillage

Field experiments were conducted to determine decomposition patterns of red clover (Trifolium pratense), field pea (Pisum sativum), canola (Brassica rapa) and wheat (Triticum aestivum) residues under zero and conventional tillage. Crop residue amounts produced in 2 trial years ranged from 1.6 t ha -1 for monoculture wheat to 6.05 t ha -1 for peas, and tillage had no effect. The extent of dry matter (DM) decomposition was usually less under zero than under conventional tillage, e.g., 31 to 41% of canola DM decomposed under zero tillage while 41 to 50% decomposed under conventional tillage in 12 mo. Corresponding percentages for other residues under zero and conventional tillage, respectively, were: 65 and 75% for clover, 43 and 45 to 55% for pea, and 27 and 40% for wheat. The rate and extent of DM decomposition were positively correlated with N and P concentrations, and negatively correlated with C/N, C/P, lignin/P and lignin/K ratios. These decomposition patterns have implications for nutrient release and soil cover. Rapid decomposition is not necessarily desirable because the nutrients released are subject to losses in soil. Key words: Biological soil quality, crop residue quality, crop rotation