Hangs, R.D.

Schoenau, J.J.

English

University of Saskatchewan Research Archive

Second-Year Decomposition and Nutrient Release Characteristics of Ten AnnualCrop Residues in South-Central Saskatchewan, CanadaRyan Hangs and Jeff SchoenauDepartment of Soil Science, University of Saskatchewan, Saskatoon, SKMATERIALS & METHODS• Post-harvest residues were collected in the fall of 2015 from farmfields in Saskatchewan, dried to a constant weight, and a 5-gsubsample placed in a polyethylene screen bag (20 × 20 cm; 1 mmmesh) and stapled closed. Additional subsamples of the originalresidues (i.e., time = 0) were analysed for their nitrogen (N),phosphorus (P), potassium (K), and sulfur (S) contents.• Prior to snowfall, the litter bags (n = 4) were placed on the soilsurface of a farm field in south-central Saskatchewan andarranged in a completely randomized design.• The soil is an Orthic Brown Chernozem with pH 7.6 and 20 mg/kgextractable NO3-N, 10 P, 300 K, and 25 S in the 0-15 cm depth.• Four collection times were chosen: the spring of 2016 (sixmonths) and the fall of 2016 (1 year), 2017 (2 years; reported here),and 2018 (3 years).• The residual litter was dried to a constant weight, weighed todetermine mass loss, and analysed for its N, P, K, and S contents.• Meteorological data (air temperature, rainfall, relative humidity,wind speed, and snow depth), along with soil temp/moisture (0-60cm), are being collected using an adjacent MET station.OBJECTIVE• Quantify the mass loss and changes in nutrient content ofdecomposing harvest residues from a variety of annual cereal,pulse, and oilseed crops grown in Saskatchewan: barley, wheat,oats, field pea, lentil, soybean, faba bean, canola, flax, and hemp.• Post-harvest plant residues represent a significant addition ofcarbon (C) and nutrients to soil; however, limited work has beendone to investigate their fate within low disturbance agriculturalsystems, where these residues are not incorporated into the soil.• Quantifying these dynamics will improve our understanding ofhow different crop residues impact C sequestration and nutrientcycling, along with providing data for the development andvalidation of agroecosystem C and nutrient biogeochemicalcycling models.INTRODUCTIONCONCLUSION• Despite similar mass (and C) losses, there were considerabledifferences in nutrient release among crop residues after twoyears, with initial residue quality being an important factorcontrolling decomposition and nutrient release, particularly for N.• Similar measurements after a third year will provide more insightinto longer term residue biomass and nutrient dynamics.• The differences in mass loss (20-83%) and cumulative N, P, K, andS release (-5 to 86%) among the crop residues (Figs. 1 and 2), areattributed to variation in specific surface area and residue quality.• Average residue N, P, K, and S additions to the soil nutrient pooldiffered among nutrients (10, 1, 15, and 2 kg/ha, respectively) andcrop residue (Fig. 3). Unlike the legume and oilseed crop residuesthat contributed N via net mineralization (19 and 12 kg N/ha), thecereal crop residues immobilized soil N (-4 kg N/ha). There wereno apparent P, K, and S loss trends among residues.• Generally the cereal residues (especially oats) are decomposingand releasing nutrients slower than other residues, explained bywider C:nutrient ratios (Figs. 1, 2, and 3). Potassium is readilyleached from all residues, leading to residue K being the largestcontribution to the soil nutrient pool.• Principal component analysis indicated: i) soil nutrient pooladditions were directly related to initial residue nutrientconcentrations, and ii) the relationship between mass loss and N,P, and S release (inverse) and K (direct), that reflects the releasemechanism of N, P, and S (microbially mediated) vs K (leaching).DISCUSSIONRESULTSFigure 1. Mean (n = 4) initial ratios of total carbon (C) to nitrogen (N),phosphorus (P), potassium (K), and sulfur (S) of post-harvest cropresidues, along with their mass and cumulative N, P, K, and S losses aftertwo years, measured using litter bags placed on the soil surface, at a sitein south-central Saskatchewan. Means with the same letter are notsignificantly different (P > 0.05) using LSD.C:N 102 127 113 50 37 39 59 86 102 91C:P 484 1403 1151 648 396 347 1009 807 1016 897C:K 247 597 868 450 523 193 1130 507 896 647C:S 80 216 91 114 143 67 69 128 93 85-100102030405060708090100MassNPKS2 YrsBarleySpringWheat OatsField PeaSoybeanLentil Canola Flax HempFabaBeanccdcbcaabcabcabcdebabcabcLoss (%)Figure 2. Ten annual crop residues before (left) and after (right) two years ofdecomposition, measured using litter bags placed on the soil surface.Original Two YearsBarleySoybeanCanolaFaba BeanField PeaFlaxHempSpring WheatOatsLentilACKNOWLEDGEMENTS• Thanks to NSERC and ADF for funding, along with the logistical support from L.Cowell, R. de Freitas, B. Ewen, C. Fatteicher, S. Froese, K. Gudkova, R. and R.Hangs, N. Howse, M. Jaster, R. Kar, T. King, L. Schoenau, C. Stevenson, A.Stocki, B. Swerhone, R. Vinueza, and J. Wiens.Figure 3. Mean (n = 4) (a) percent change in nitrogen (N), phosphorus (P),potassium (K), and sulfur (S) content of decomposing annual crop residuesafter two years, measured using litter bags placed on the soil surface, and (b)its predicted effect on soil nutrient availability, estimated by factoring in theinitial residue nutrient concentrations, historically reported crop residuebiomass, and change in nutrient content. For each nutrient, means with thesame letter are not significantly different (P > 0.05) using LSD.2 Yrs-10-505101520253035Soil Nutrient Budget (kg/ha)N P K SSpringWheatOatsBarleyField PeaSoybeanLentil Canola Flax HempFabaBeanbeeffdefadcbgbcdcaccd d ffabda bec fbabdaeccdebb2 Yrs-50-250255075100Nutrients Released (%)N P K Scdebcbcdcfe ffcdebc dbc abeabddbcababcbcaaaabbcdcdabababdabadbcdea2 Yrs-10-505101520253035Soil Nutrient Budget (kg/ha)N P K SSpringWheatOatsBarleyField PeaSoybeanLentil Canola Flax HempFabaBean

Second-year decomposition and nutrient release characteristics of ten annual crop residues in south-central Saskatchewan, Canada

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Second-year decomposition and nutrient release characteristics of ten annual crop residues in south-central Saskatchewan, Canada

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