Decomposition Dynamics of Leaf Litter Mixtures Enriched with NPS Fertilizer and Resultant Effects on Common Bean Productivity in Nutrient Depleted Soil

Abstract

Organic materials have a nonreplaceable role to improve soil quality and productivity. Yet, processes related to decomposition and nutrient supply capacity are restricted under nutrient-depleted soils. Thus, a field experiment was conducted to evaluate the decomposition rate of leaf litter mixtures treated with mineral nitrogen (N), phosphorous (P), and sulfur (S) fertilizer in the form of NPS (19N38P2O57S), and their effects on agronomic performance of common bean (Phaseolus vulgaris L.). The mixtures of croton (Croton macrostachyus) and erythrina (Erythrina brucei) leaf litters (LLs) were placed at 20 cm depth in a litterbag at a rate equivalent to 2.5 and 5 t/ha, and treated with four NPS rates (0, 50, 100, and 150 kg/ha). The leaf litters have low carbon (C) to N ratio. The experiments (litterbag and crop response) were laid out in a randomized complete block design with three replications. The decomposition pattern was monitored at a two week interval (15, 30, 45, and 56 days after application) and assessed for daily decomposition rate (k), weight loss, and time required to decompose half of the residue (t50). For the crop response experiment, selected growth and yield component parameters, and grain yield data were recorded. The results indicated that NPS fertilizer and the amount of LL were significantly ( $p<0.01$ ) influenced the k values and weight loss. The k at 14 days varied from 4.47% day−1 (150 NPS kg/ha × 2.5 t LL/ha) and 2.75% day−1 (sole 2.5 t/ha LL) in which application of mineral NPS fertilizer enhanced k by 62.5%. The k values, averaged over 56 days, revealed 2.68% day−1 (150 kg NPS/ha × 2.5 t LL/ha), and 1.78% day−1 in the unfertilized 2.5 LL. The decay rate was faster within 14 days and declined afterward. Over 56 days, 60.4% and 46.6% of the original mass remained in litters without NPS fertilizer, and 150 NPS kg/ha x 2.5 t LL/ha, respectively. The residue weight loss also significantly decreased with time (r2 > 0.98). Half-lifetime was significantly ( $p<0.001$ ) decreased with the increasing rate of NPS application (r = −0.86). The t50 values, averaged over 56 days, were between 38.9 days (nontreated LL) and 27.8 days (150 kg NPS/ha), respectively. The result regarding agronomic performance indicated that the application of NPS fertilizer on the leaf litters significantly ( $p<0.01$ ) increased the growth, yield component, and grain yield of common bean. For instance, 150 kg NPS/ha on 2.5 t/ha LL has resulted in a 79% grain yield advantage over LL without NPS. Grain yield also showed significant relationship ( $p<0.01$ ) with k (r = 0.67), mass loss (r = −0.67), and t50 (r = −0.66). The finding suggests that for plant residues with a narrow C/N ratio in nutrient-depleted soils, the addition of mineral NPS fertilizer is advantageous for increased decomposition and yield of legume crops.