Long-term straw management and N fertilizer rate effects on quantity and quality of organic C and N and some chemical properties in two contrasting soils in Western Canada

Crop residue and fertilizer management practices alter some soil properties, but the magnitude of change depends on soil type and climatic conditions. Field experiments with mainly barley (and canola, wheat, triticale, or pea in a few years) under conventional tillage were conducted from 1983 to 2009 at Breton (Gray Luvisol (Typic Haplocryalf) loam) and Ellerslie (Black Chernozem (Albic Argicryoll) clay loam), Alberta, Canada, to determine the effects of straw management (straw removed (SRem) and straw retained (SRet)) and N fertilizer rate (0, 25, 50, and 75 kg N ha−1) on total organic C (TOC) and N (TON), light fraction organic C (LFOC), and N (LFON) in the 0–7.5 and 7.5–15 cm, pH in the 0–7.5, 7.5–15, and 15–20 cm and extractable P, ammonium-N, and nitrate-N in the 0–15, 15–30, 30–60, and 60–90 cm soil layers. The SRet and N fertilizer treatments usually had higher mass of TOC, TON, LFOC, and LFON in soil at Breton, but only of LFOC and LFON in soil at Ellerslie compared with the corresponding SRem and zero-N control treatments. The responses of soil organic C and N to management practices were more pronounced for N fertilization than straw management. There were significant correlations among most soil organic C or N fractions, especially at Breton. Linear regressions between crop residue C or N input, or rate of fertilizer N applied and soil organic C or N were significant in most cases at Breton, but only for LFOC and LFON at Ellerslie. At Breton, compared with zero-N rate, the C sequestration efficiency of additional crop residue C input was 5.8%, 20.1%, and 20.4% in SRet and 17.2%, 28.0%, and 30.1% in SRem treatments at the 25, 50, and 75 kg N ha−1 rates, respectively. The effects of crop residue management and N fertilization on chemical properties were generally similar for both contrasting soil types. There was no effect of crop residue management on soil pH, extractable P and residual nitrate-N. Extractable P and pH in the top 0–15 cm soil decreased significantly with N application in both soil types. Residual nitrate-N (though quite low in Breton soil) increased with application of N and also indicated some downward movement in the soil profile up to 90 cm depth in Ellerslie soil. There was generally no effect of any treatment on ammonium-N in soil. In conclusion, straw retention and N application improved organic C and N in soil, and generally differences were more pronounced for light fraction than total organic C and N, and between the most extreme treatments (SRem0 vs. SRet75). Application of N fertilizer reduced extractable P and pH in the surface soil, and showed accumulation and downward leaching of nitrate-N in the soil profile.