Soil aggregation and greenhouse gas flux after 15 years of wheat straw and fertilizer management in a no-till system

• Published in: Soil & tillage research 2013-01, Vol.126, p.78-89
• Main Authors: Lenka, Narendra Kumar, Lal, Rattan
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Alfisols; Biological and medical sciences; carbon; Carbon sequestration; CO2 – mitigation; correlation; Crop residue; Cropping systems. Cultivation. Soil tillage; fertilizer rates; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Generalities. Analysis and diagnosis methods; global warming; Global warming potential; greenhouse gases; management systems; microaggregates; nitrogen content; nitrogen fertilizers; Occluded carbon; Physical properties; Physics, chemistry, biochemistry and biology of agricultural and forest soils; silt; Soil aggregates; soil depth; soil organic carbon; soil properties; Soil science; Soil-plant relationships. Soil fertility. Fertilization. Amendments; Structure, texture, density, mechanical behavior. Heat and gas exchanges; Triticum aestivum; wheat straw
• ISSN: 0167-1987; 1879-3444
• DOI: 10.1016/j.still.2012.08.011

► The soil-, aggregate- and occluded C significantly influence greenhouse gas (GHG) flux from soil. ► The microaggregate C is relatively protected but the occluded C in macroaggregates is not stabilized. ► The mitigation potential of residue retention decreases with time and rate of addition. ► With 15 years of mulch application, the soil may be approaching its SOC sink capacity. ► Residues had dominant effect than fertilizers, in terms of aggregation and the GHG flux. Mulching effect on carbon (C) sequestration depends on soil properties, mulch material, and the rate and duration of application. Thus, rate of soil C sequestration was assessed on a 15 year field study involving three levels of wheat straw at 0 (M0), 8 (M8) and 16 (M16) Mgha−1yr−1, at two levels (244kgNha−1yr−1, F1 and without, F0) of supplemental N. Soil C concentration was assessed in relation to aggregation and occlusion in aggregates of a silt loam Alfisol under a no-till (NT) and crop-free system in central Ohio. In comparison to control, soil organic carbon (SOC) concentration in the 0–10cm depth of bulk soil increased by 32% and 90% with M8 and M16 treatments with a corresponding increase in the SOC stock by 21–25% and 50–60%, respectively. With increase in rate of residue mulch, proportion of water stable aggregates (small macroaggregates, >250μm size) increased by 1.4–1.8 times and of microaggregates (53–250μm) by 1.4 times. Fertilizer N significantly increased the SOC concentration of small macroaggregates under M16 treatments only. Ultra-sonication showed that 12–20% of SOC occluded in the inter-microaggregate space of small macroaggergates, was a function of both mulch and fertilizer rates. Significantly higher and positive correlation of greenhouse gases (GHGs), CO2, CH4 and N2O flux was observed with C and N concentrations of small macroaggregates and also of the occluded fraction of small macroaggregates. The higher correlation coefficient indicated the latter to be prone to microbial attack. On the contrary, non-significant relationship with C and N concentrations of microaggregates indicate a possible protection of microaggregate C. The diurnal fluxes of CO2, CH4 and N2O were the lowest under bare soil and the highest under high mulch rate with added N, with values ranging from 1.51 to 2.31gm−2d−1, −2.79 to 3.15mgm−2d−1 and 0.46 to 1.02mgm−2d−1, respectively. Mulch rate affected the GHGs flux more than did the fertilizer rates. The net global warming potential (GWP) was hig