Evaluation of Nitrogen Mineralization Dynamics Following Amendments Application under Cropping Systems on a Ferric Acrisol in Ghana

Abstract

Published information on the dynamics of nitrogen mineralization under different amendments and cropping systems on the field is lacking. Earlier studies focused on nitrogen mineralization under laboratory conditions, results of which may be of limited importance under field conditions. To bridge this gap in knowledge, a field experiment was conducted on a Ferric Acrisol in 2006 and 2007 in the semi – deciduous forest zone of Ghana. The experiment was arranged in a split – plot with three replications. Three different amendments (poultry manure, poultry manure + chemical fertilizer, chemical fertilizer and a control (no amendment) constituted the sub-plots whereas selected cropping systems (continuous maize, maize/soybean intercrop and maize/cowpea rotation) were assigned to the main plots. The experiment was conducted in three consecutive cropping seasons and the rate of nitrogen mineralization monitored at 3, 6, 9 and 12 weeks after application of amendments (WAA) within each season. The results indicated changes in the level of NO3- and NH4+ over time. Nitrate- nitrogen was generally low and rose to higher levels at the occurrence of ‘Birch effect’ when the control registered higher values (19.32 - 80.89 mg NO3- kg-1 soil) than amended plots (12.83 - 80.49 mg NO3- kg-1 soil). Unlike NH4+ - N, NO3- - N showed immobilization in amended plots as PM and PM + CF plots recorded -0.11 mg/kg each at 9 WAA in 2007 major season. The ratios of NH4+ -N: NO3- -N varied considerably in the seasonal cycles with generally least values (0.1 - 1.3) recorded at the occurrence of Birch effect. Cropping systems significantly (P < 0.05) influenced NH4+ -N: NO3- -N ratios in all seasons of study. The study has established that ‘Birch effect’ is characterized by immobilization of nitrate under amendments and lower NH4+: NO3- ratios. Crop removal of NO3- - N and NH4+ - N was generally different for the cropping systems considered.