Nutrient leaching in an Ultisol cultivated with sugarcane

Solute leaching below the crop-rooting zone represents not only a valuable loss of nutrients for the plant, but also a potential pollution source of groundwater. The objective of this work was to quantify nutrient-leaching losses at 0.9m depth in an Ultisol that was cultivated with sugarcane, located in the county of Jaboticabal-SP, Brazil. The following ions were evaluated: nitrite, nitrate, ammonium, sulfate, phosphate, calcium, magnesium and potassium. The first ratoon cycle was monitored from November 16, 2006, to July 9, 2007. The experimental design was organized as four random blocks and three treatments: T1: without fertilizer; T2: 100kgha−1 of N and 114kgha−1 of S; and T3: 150kgha−1 of N and 172kgha−1 of S. To determine the fate of the N-fertilizer and S-fertilizer, four microplots were installed, in which 2.15% atoms of 15N- and 10.5% atoms of 34S-enriched ammonium sulfate were applied. The input and output of anions and cations were quantified from the flux density of water and the ion concentration. The NO3−, K+, Mg2+ and Ca2+ concentrations in the soil increased in January following both rainfall and drainage. The leaching of N was between 3.9 and 34.9kgha−1. The N leached derived from the 100kgha−1 applied N fertilizer was 22.5kgha−1. The S leached was between 4.6 and 8.4kgha−1. From the 114kgha−1 S applied as fertilizer the leaching was 0.480kgha−1. The maximum leaching of P, K, Ca, and Mg were 1.2, 53.6, 135.7 and 39.8kgha−1, respectively. From the results, it is not possible to determine whether the local groundwater will be contaminated, but caution should be taken to maintain soil quality by reducing the leaching loss of nutrients.