C and N mineralisation of straw of traditional and modern wheat varieties in soils of contrasting fertility
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Incorporation of crop residues can increase SOC stocks, but the extent of this depends on their C:N ratio and soil nutrient availability. Traditional wheat varieties (TWV) typically produce high straw biomass with high C:N ratio. We hypothesised that C:N ratio of straw of TWV are higher than those of modern (MWV) ones, resulting in lower carbon (C) mineralisation potential, especially in nutrient-poor (NP) soils. Furthermore, soil nitrogen (N) retention is expected to be higher during decomposition of straw of TWV with high C:N ratio. Straw productivity of six TWV and six MWV was measured during a 2-year field experiment, in nutrient-rich (NR) and NP soils. Cumulative CO2 emissions and soil N availability were also examined in these soils amended with straw residues with C:N ratios of 89.2, 148.6 and 202.7 during an 84-day lab experiment. Straw production of TWV was 1.31–1.74 times higher compared to MWV. Straw C:N ratio of TWV in NP soil averaged 152.1, greater than that of MWV (119.8). Straw-derived CO2 emissions in NR soils were 2.5–4.3 times higher than NP and were the lowest in straw C:N ratio of TWV. After the addition of straw, immobilised N was partially re-mineralised in the NR soil with lower values at higher straw C:N ratio. N immobilisation also occurred in straw amended NP soil independently of the straw residues C:N ratio. The higher straw productivity and higher C:N ratio of TWV can contribute to C accumulation and prevent N losses after its incorporation in soils.
KeywordsTraditional and modern wheat varieties C:N ratios of wheat straw residues CO2 production Soil N dynamics
This work springs from the international research project on Sustainable Farm Systems: Long-Term Socio-Ecological Metabolism in Western Agriculture funded by the Social Sciences and Humanities Research Council of Canada (SSHRC 895-2011-1020) and Spanish research projects HAR2012-38920-C02-01 and HAR2015-69620-C2-1-P funded by Ministerio de Econoñmía y Competitividad (Spain).
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