First-Year Decomposition and Nutrient Release Characteristics of Ten Annual Crop Residues in South-Central Saskatchewan, Canada.

Quantifying crop residue decomposition will help to improve our understanding of carbon sequestration and nutrient cycling within agroecosystems, while providing valuable data for model development and validation. The objective of this study is to quantify the decomposition and associated nutrient release dynamics of post-harvest residues from a variety of annual cereal, pulse, and oil seed crops grown in Saskatchewan: barley, wheat, oats, field pea, soybean, faba bean, lentil, canola, flax, and hemp. Litter bags were placed on the soil surface in the fall of 2015 prior to snowfall and will be collected in the spring of 2016 (six-months), fall 2016 (1-yr), fall 2017 (2-yrs), and fall 2018 (3-yrs), to model the rates of mass loss and release of nitrogen (N), phosphorus (P), potassium (K), and sulphur (S) to the soil nutrient pool. After one year, the differences in mass loss (27-41%) among the crop residues, along with the corresponding N, P, K, and S additions to the soil (9, 1, 12, and 2 kg/ha, respectively), are attributed to varying residue quality and specific surface area. Hemp residue had the largest mass loss, likely due the decomposition of its narrower C:N components (e.g., flowers, leaves, and hurd; ≤ 40). The grain legume crop residues contributed more N via net mineralization than cereal crop residues (15 vs 2 kg N/ha), with no apparent P, K, and S loss trends among residues. The apparent relationship between mass loss and N, P, and S release (inverse) and K (direct), may reflect the contrasting release mechanism of N, P, and S (microbially mediated) vs K (leaching). Measurements over subsequent years will allow for the modelling of decomposition rate constants and limit values associated with carbon and nutrient additions to soil over time for each residue type.