Changes in soil organic carbon and nitrogen fractions on conversion of land use from long term poplar based agroforestry to rice–wheat rotation
摘要
There is limited information on what happens to soil carbon and nitrogen fractions when long-term poplar based agroforestry system (AFS) is converted to rice–wheat cropping system. Therefore, a study was conducted to observe the changes in soil carbon and nitrogen pools when land use was changed from long term poplar based AFS to rice–wheat rotation at Khera bet village, Ludhiana, Punjab. The observations were recorded in four land use systems viz., sites where poplar based AFS was being raised for the last 35 years, sites with rice–wheat rotation system for last 35 years, sites with rice–wheat rotation from the last 5 years which was converted from poplar based AFS for 30 years and uncultivated fallow land with no crop or plants (control). Soil organic carbon (SOC) content was highest in poplar based AFS (8.0 g kg−1 in surface depth) and lowest in control (3.82 g kg−1). Very labile (2.396–3.132 g kg−1) and labile carbon (2.264–2.840 g kg−1) pools were also higher under poplar based AFS, whereas less labile (1.684–2.602 g kg−1) and non-labile carbon (2.744–2.984 g kg−1) pools were higher under long term rice–wheat rotation system. All the fractions decreased with depth in various land use systems. Microbial biomass and water soluble carbon ranged from 44.0–149.0 μg kg−1 and 8.46–17.19 mg kg−1, respectively in 0–15 cm soil depth in various land use systems. Carbon pool index, lability index and carbon management index were higher under poplar based AFS than other systems. The ammonical and nitrate N were observed to be highest under long term rice–wheat rotation, with a range of 6.31–7.49 and 3.29–4.42 mg kg−1, respectively. Therefore, it is concluded that the readily decomposable carbon fractions were higher in poplar based AFS whereas more stable carbon fractions in rice–wheat cropping system.