Stable isotope technique in the evaluation of tillage and fertilizer effects on soil carbon and nitrogen sequestration and water use efficiency

Abstract Agricultural soil could be made to serve as a sink rather than a source of greenhouse gases by suitable soil management. This study was, therefore, conducted to assess the impact of tillage and fertilizer application on soil and plant carbon and nitrogen fractionation and intrinsic water use efficiency ( i WUE). The experiment was a split–split-plot factorial design with three replications. The main plot consisted of two tillage treatments: zero tillage (ZT) and conventional tillage (CT). The sub-plot contained four NPK fertilizer treatments (0, 90, 120 and 150 kg N ha −1 ), while the sub–sub-plot comprised three poultry manure (PM) treatments (0, 10 and 20 Mg ha −1 ). Soil carbon and nitrogen sequestration were evaluated using stable isotope of carbon ( δ 13 C) and nitrogen ( δ 15 N). The δ 13 C in maize plant was used to obtain i WUE. It was observed that soil δ 13 C and δ 15 N were more depleted under ZT than CT and in plots treated with 20 Mg ha −1 PM (PM 20 ) implying carbon and nitrogen sequestration under ZT and by PM 20 . Relative to the control, application of PM 20 raised soil δ 15 N enrichment by 82% and 96% under CT and ZT, respectively. Higher i WUE of 25.7% was obtained under CT and was significantly higher than the i WUE values under ZT in the second year of the study while the i WUE was significantly lower with PM 20 application than other fertilizer treatments. The significant δ 13 C depletion and hence lower i WUE with combination of NPK fertilizer and PM under CT than the control implied that soil disturbance under tilled plots was mediated by combined nutrient management thereby limiting soil C available for fractionation resulting in lower i WUE. This suggests that conservation tillage such as zero tillage and integrated application of organic and inorganic fertilizers are good strategies for reducing soil carbon and nitrogen emission.