Effects of irrigation, crop residue mulch and nitrogen management in maize (Zea mays L.) on soil carbon pools in a sandy loam soil of Indo-gangetic plain region

Different land use management practices e.g. native forest vegetation, pastures and the agricultural management practices (e.g. tillage, cropping system, crop residue mulching and fertilizer and manure application) influence the soil organic carbon pools, which has short term and long term implications on soil carbon dynamics. Field experiments were conducted in a sandy loam soil of the Indian Agricultural Research Institute, New Delhi research farm during the kharif season (July to October) of 2012 and 2013 with the objective to study the short term (2 years) impact of irrigation, crop residue mulch and nitrogen management in maize on soil organic carbon pools and to identify the best management practice in terms of Carbon Management Index (CMI). Maize (cv. HQPM 1) was grown in a split-split plot design with two levels of irrigation (irrigated and rainfed) as main factor, two levels of mulch (No mulch and wheat residue at a rate of 10 Mg/ha as mulch) as sub factor and three levels of nitrogen (0, 75 and 150 kg N/ha) as subsub factor. The results showed that total organic carbon (TOC) increased by 40.5% in irrigation treatment compared to the rainfed treatment for the 0-5 cm soil depth after 2nd year of cropping. Application of crop residue mulch significantly increased the TOC concentration by 14.9% at 0-5 cm soil depth compared to the no mulch treatment. Crop residue mulch also significantly increased carbon stratification ratio (SR) by 9.2% compared to no mulch treatment for the same depth. Nitrogen application at 150 kg/ha significantly increased TOC concentration at 0-5 cm soil depth by 22.2% and 7.8% over control and 75 kg/ha, respectively. Water stable aggregate associated carbon concentration in large macro-aggregates and micro-aggregates increased significantly by 16.7% and 11.8%, respectively due to crop residue mulching. Application of crop residue mulch resulted in significant increase in labile and non-labile pools of carbon at 0-5 cm soil depth compared to the no mulch treatment, and among the labile pools of carbon, the maximum increase was recorded in very labile (VL) pools. The Carbon Lability Index (CLI) decreased whereas Carbon Pool Index (CPI) and Carbon Management Index (CMI) increased due to irrigation and crop residue mulch application. Application of 75 kg N/ha resulted in significantly higher CMI than that of 150 kg N/ha at 0-5 and 5-15 cm soil depth. So maize may be grown under irrigated condition with wheat residue mulch at a rate of 10 Mg/ha and 75 kg N/ha to achieve higher total organic carbon pool and labile pools of carbon, better Carbon Management Index.