Nitrate leaching and pasture yields following the application of dairy shed effluent or ammonium fertilizer under spray or flood irrigation: results of a lysimeter study

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Abstract
Nitrate leaching and pasture (Lolium perenne / Trifolium repens) yields were measured on monolith lysimeters (80 cm diam. × 120 cm depth) of a Templeton sandy loam soil (Udic Ustochrept), following repeated applications of dairy shed effluent (DSE) or ammonium fertilizer (NH4Cl), under spray (50 mm/month) or flood (100 mm/month) irrigation. Applications of DSE at 400 kg N/ha per annum resulted in significantly less nitrate leaching (8–25 kg N/ha per yr) compared with NH4Cl (28–48kg N/ha per yr) (P < 0.01). Over the two year period, the total mineral N (predominantly nitrate) leached was equivalent to 2.5–3.7% of the total N applied in the DSE and 8.7–9.8% of the N applied in the NH4Cl. There was a trend of slightly less nitrate leaching under the flood irrigation than under the spray irrigation, probably because of the greater potential for denitrification under the wetter conditions. Average nitrate concentrations in the leachate were generally below the drinking water standard except in the NH4Cl treatment under spray irrigation where it averaged 10 mg NO3‐N/l over the two year period. DSE was equally as effective as NH4Cl in stimulating pasture dry matter production. Annual nitrogen uptakes were similar for the DSE (343 kg N/ha) and NH4Cl (332–344kg N/ha) treatments in the first year but were higher in the DSE (361–412 kg N/ha) than in the NH4Cl (324–340 kg N/ha) treatments in the second year. Pasture uptakes of phosphorus and sulphur were also higher in the DSE than in the NH4Cl treatments in the second year. The results emphasize the need to set different regulatory limits for land application of organic wastes of various types and for N fertilizers.