Sugarcane green harvest management influencing soil phosphorus fractions

Few researchers have evaluated phosphorus (P) fractions in soils from humid tropical regions in which sugarcane (Saccharum spp) is harvested without prior burning. Aiming to evaluate if that practice may promote substantial changes in the availability of soil P, we analyzed the differences in total P, organic P (Po), and extractable inorganic P (Pi) fractions in soil samples collected from an Oxisol. A long-term (14 years) randomized block design was employed with six replicates and two treatments: green-harvest (GH) and burned-harvest (BH) in a sugarcane plantation. Soil samples, with six replicates, were collected at depths of 0-0.05 m, 0.05-0.1 m, 0.1-0.2 m, 0.2-0.3 m, and 0.3-0.4 m from the planting row, 0.25 m perpendicular to the row, and in the interrow. The total Po fraction had the greatest variation between the GH and BH systems. Total Po concentration was lower in the 0-0.05 m soil layer of the GH system than that of the BH system. Total Po had also accumulated in the 0.2-0.3 m layer, which is where P fertilizer was applied at planting. These differences were observed in the planting row and 0.25 m from the planting row, but not in the inter-row. There was also no relationship between Pi fractions and row position or sampling depth in the two harvest systems. Long-term GH management rather than conventional BH sugarcane promoted greater cycling of Po in the soil, while concentrations of Pi fractions did not differ between harvest systems.