Leaching of nitrate and other nutrients from a grazed pasture

The object of this study was to determine the amounts of nitrate (NO 3 ‐ ) and other nutrients leached from an intensively grazed pasture over 1 year. Concentrations of NH 4 + , NO 3 ‐ , Ca 2+ , Mg 2+ , Na + , K + , SO 4 2‐ , PO 4 3‐ , and Cl ‐ were measured in samples of water percolating through soil (Ruatangata friable clay) under cattle grazed pastures receiving 0 or 172 kg N/ha per year as urea. Elemental concentrations varied greatly with both site and time of collection. The equivalent concentrations of NO 3 ‐ and Ca 2+ were highly correlated ( r 2 = 0.96) and could be used for estimating the equivalent concentrations of the other ions. For each unit increase in the concentration of NO 3 ‐ , the equivalent concentration of cations increased in the order: Ca > Mg > Na > K. The amount of element leached was calculated as the product of measured concentration and estimated drainage volume. Leaching losses over 1 year (kg/ha nil‐N treatment; kg/ha +N treatment) were thus estimated as N (88; 193); Ca (154; 216); Mg (32; 44); Na (71; 86); and K (14; 21). Rainfall and estimated drainage were 1840 and 985 mm respectively.