Mineral nitrogen dynamics in compacted soil under organic amendment

Abstract Soil compaction is a major problem associated with conventional agriculture characterized by heavy farm machinery usage. However, only few studies have quantified the dynamics of soil nutrients in compacted soils under restorative interventions, particularly in sub-Saharan Africa. Field and pot experiments were therefore conducted to evaluate the extent to which soil compaction modulates NH4+ and NO3− dynamics under organic amendment in Ghana. Soils were bulked to three (1.3, 1.5, and 1.7 Mgm−3) and four (1.3, 1.5, 1.7 and 1.9 Mgm−3) density levels in field and pot experiment respectively. The treatments were laid out in a factorial experiment, replicated three times with poultry manure applied at 4 and 6 t ha−1 with a control (0 t ha−1). Mineral N generally increased from 21 to 42 days after amendment (DAA) and declined at 63 DAA in both experiments. Soil compaction decreased NO3− more than NH4+ levels, the effects being more pronounced at 21 and 63 DAA in the field experiment. Application of poultry manure (PM) at 6 t ha−1 offsets, to a large extent, the impact of soil compaction. The 4 and 6 t ha−1 PM produced similar (p > 0.05) grain yields of 3000.00±169.04 and 3004.44±277.99 kg ha−1 in the field experiment respectively. However, grain yield decreased by 135% in compacted soil at 1.7 Mgm−3, which received no amendment, compared to same compacted soil that received 4 t ha− 1 poultry manure in the field experiment. Our finding suggests that addition of 4 t ha−1 PM is required for yield improvement in compacted soils less than 1.5 Mgm−3.