Biomass amendment effects on soil nutrients and microbial phosphorus under different land uses in a tropical dryland

Abstract

Dryland agriculture is constrained by limited water availability, low organic matter and increasing erosion. In sloping dryland areas of eastern Indonesia, slash-and-burn land preparation can reduce soil fertility. This study examined the effects of five biomass amendments (control, rice husk charcoal (RHC), wood charcoal (WC), rice husk (RH) and wood leaves (WL), each at 20 t ha-1) on soil chemical properties and microbial phosphorus (microbial P) in two land-use systems, intensive cultivation (IC) and non-intensive cultivation (NIC), sampled at two sites (Netpala and Kualeu, Indonesia) and incubated for 30 and 60 days. Using a randomised complete block design (RCBD) with site as the blocking factor, biomass treatment significantly increased total nitrogen (N), phosphorus pentoxide (P₂O₅) and potassium oxide (K₂O) in IC soils (p < 0.05), whereas effects in NIC soils and effects on pH, organic carbon (C) and microbial P in either soil type, were not statistically significant at the achieved replication. Intensive cultivation soils showed larger numerical gains relative to their own controls than NIC soils, which maintained higher absolute nutrient levels throughout; wood leaves produced the largest gains in N and K₂O, while charcoal amendments produced the largest gains in P₂O₅ and organic C. These findings, based on a high, non-field-representative rate and two-site incubation, indicate that biomass amendments can improve short-term soil chemical status in degraded tropical dryland soils, most clearly under intensive cultivation; field trials at realistic rates with greater replication are needed to confirm their practical value for restoring soil quality and reducing degradation from slash-and-burn practices.