Long term sugarcane cultivation on tropical Ultisols drives changes in available phosphorus and arbuscular mycorrhizal colonization and soil quality indicators

Abstract

Chemical, physical and biological indicators of soil condition are seldom assessed together across a crop cycle on tropical Ultisols. We examined how selected soil quality and arbuscular mycorrhizal (AMF) indicators differ among sugarcane crop stages. Twenty plots at three commercial plantations in South Sumatra, Indonesia, were sampled at four crop stages (3, 5, 7 and 11 months; n = 6, 6, 4 and 4). Soil pH, organic carbon (SOC), Bray-1 available phosphorus (P), aggregate stability (mean weight diameter, MWD), bulk density, AMF spore density, root colonization, Shannon diversity and stalk height were measured, with yield and Pol at harvest. Analyses used one- and two-way ANOVA, correlation, principal component analysis, a soil quality index (SQI) and resampling procedures suited to the modest sample size. Stage mean available P was 66.1, 11.7, 18.3 and 15.3 mg kg⁻¹ at 3, 5, 7 and 11 months. AMF spore density and root colonization were highest at 5 months, and colonization was negatively correlated with available P, although that association is a contrast between the 3-month plots and all others. Plots at later stages had higher MWD, lower bulk density and higher SOC concentration, although SOC stocks differed little. Stage differences persisted after adjustment for site and no stage × site interaction was detected, but two of three sites contributed one block per stage. The SQI ranked the earliest stage lowest, a result determined by construction. These observational findings motivate experimental testing of phosphorus timing.