Residual effect of nitrogen on rice productivity following tree removal of Acacia nilotica in a traditional agroforestry system in central India

Abstract

The study reports the effect of residual nitrogen on the yield of rice crop after removal of Acacia nilotica (L.) wild. ex. Del. tree in a traditional agroforestry system in central India. Twenty four homogeneous rice fields were selected. These were divided into six sets of four fields each. From these sets, trees had been removed 1–5 years and 7 years, respectively before the beginning of the study. There was only one tree stump in each field. Rice crop and soil were sampled at 1–7 m and 20 m distance from the tree stump. Distance at 20 m was treated as control. Maximum 53% of the residual nitrogen was released quickly for the first rice cropping season following the tree removal and remaining 37% gradually, until the fifth cropping season. Yield of the rice crop was higher by 73%, across the distances, for the first cropping season, 52% for the second, 45% for the third, 41% for the fourth and 26% for the fifth cropping season, compared to the control. The crop yield, soil organic C and total soil N increased up to 5 m from the tree stump in the first cropping season. By the fifth cropping season, the increase due to tree removal was confined to 2 m from the stump. Total increase in the crop yield, across the cropping seasons, was 12.5 t ha −1 which was nearly equal to the reduction in the crop yield suffered during 15 years of the tree growth. Soil organic C and total soil N declined with the passage of time following the tree removal, where as C/N ratio increased.