Soil Phosphorus Reserves and Availability Under Contrasting Sugarcane Harvesting System in Umbric Rhodic Ferralsols

Abstract The impact of sugarcane harvesting system on phosphorus (P) cycling in highly weathered, acidic soils remains poorly understood, especially in Umbric Rhodic Ferralsols of South Africa. We hypothesized that green cane harvesting would increase P availability and microbial activities compared to pre-harvest burning. The aim of this study is to determine the effects of green cane relative to pre-harvest burning on soil P inorganic fractions, microbial biomass P (MBP), and the activity of acid and alkaline phosphomonoesterase enzyme activities in Umbric Rhodic Ferralsols. Soils were sampled to a 100-cm depth from adjacent fields under pre-harvest burning systems. Inorganic P fractions, Ambic-2 extractable P, MBP, and phosphomonoesterase enzyme activities were measured and analysed using a two-way ANOVA. Green cane harvesting resulted in lower soil pH and higher extractable P, citrate-dithionite-bicarbonate P (CDB-P), and P bound to aluminium (Al-P) fractions compared to pre-harvest burning. MBP was 100% higher ( p < 0.001) under green cane. Acid phosphomonoesterase activity was 82% higher ( p < 0.001), while alkaline phosphomonoesterase activity was 37% ( p = 0.022) lower under green cane than under pre-harvest burning. These findings demonstrate that green cane harvesting enhances P storage, availability, and microbial activity involved in P cycling compared to pre-harvest burning in Umbric Rhodic Ferralsols. Future work should investigate the seasonal dynamics of P availability, MBP, and phosphomonoesterase enzyme activity in relation to sugarcane P uptake.