Abstract. In grazed dairy pasture systems, a major source of NO3– leached and N2O emitted is the N returned in the urine from the grazing animal. The objective of this study was to use lysimeters to measure directly the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in decreasing NO3– leaching and N2O emissions from urine patches in a grazed dairy pasture under irrigation. The soil was a free‐draining Lismore stony silt loam (Udic Haplustept loamy skeletal) and the pasture was a mixture of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). The use of DCD decreased NO3–‐N leaching by 76% for the urine N applied in the autumn, and by 42% for urine N applied in the spring, giving an annual average reduction of 59%. This would reduce the NO3–‐N leaching loss in a grazed paddock from 118 to 46 kg N ha–1 yr–1. The NO3–‐N concentration in the drainage water would be reduced accordingly from 19.7 to 7.7 mg N L–1, with the latter being below the drinking water guideline of 11.3 mg N L–1. Total N2O emissions following two urine applications were reduced from 46 kg N2O‐N ha–1 without DCD to 8.5 kg N2O‐N with DCD, representing an 82% reduction. In addition to the environmental benefits, the use of DCD also increased herbage production by more than 30%, from 11 to 15 t ha–1 yr–1. The use of DCD therefore has the potential to make dairy farming more environmentally sustainable by reducing NO3– leaching and N2O emissions.

ABSTRACTsolution P transferred to ground or surface water depends primarily on the interplay with the flowing waterAlthough phosphate phosphorus (P) is strongly sorbed in many and its associated energy (Haygarth and Jarvis, 1999 Watson, 1980), anion exchange resin (Sibbesen, 1978), the topsoil, but the higher P-fixing capacity of the subsoil appeared and iron oxide-impregnated paper (van der Zee et al.,to restrict P mobility. Application of a dye tracer enabled preferential 1987;Pote et al., 1996; Chardon et al., 1996), as well as flow pathways to be identified. Soil sampling according to dye staining isotopic exchange (Fardeau, 1996; Di et al., 1997). These patterns revealed that exchangeable P was significantly greater in methods are used to estimate the amount of soil P that preferential flow areas as compared with the unstained soil matrix.is available for plant uptake. Recently, attempts have which there is an increased risk of significant P loss in subsurface drains. In addition, the findings of Heathwaite and Dils (2000) highlighted the importance of

Abstract. Nitrous oxide (N2O) from animal excreta in grazed pasture systems makes up a significant component (c. 10%) of New Zealand's total greenhouse gas inventory. We report an effective method to decrease N2O emissions from animal urine patches by treating the soil with the nitrification inhibitor dicyandiamide (DCD), in a simulated grazed dairy pasture system under spray irrigation. The soil was a free‐draining Lismore stony silt loam (Udic Haplustept loamy skeletal) and the pasture was a mixture of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). By treating the soil with DCD, N2O emissions were decreased by 76% following urine application in the autumn, from 26.7 kg N2O‐N ha−1 without DCD to an average of 6.4 kg N2O‐N ha−1 with DCD over the 6‐month experimental period. N2O flux was decreased by 78% following urine application in the spring, from 18 kg N2O‐N ha−1 without DCD to 3.9 kg N2O‐N ha−1 with the application of DCD over the 3‐month period. A single application of DCD immediately after urine was sufficient to effectively mitigate N2O emissions from the urine. The results showed that repeated applications of DCD after urine application, or mixing DCD with urine, offered no advantage over a single application of DCD immediately after urine deposition.

Gross N mineralization and nitrification rates were measured in soils treated with dairy shed effluent (DSE) (i.e. effluent from the dairy milking shed, comprising dung, urine and water) or ammonium fertilizer (NH 4 Cl) under field conditions, by injecting 15 N-solution into intact soil cores. The relationships between gross mineralization rate, microbial biomass C and N and extracellular enzyme activities (protease, deaminase and urease) as affected by the application of DSE and NH 4 Cl were also determined. During the first 16 days, gross mineralization rate in the DSE treated soil (4.3^6.1 mg N g 71 soil day 71 ) were significantly (P`0.05) higher than those in the NH 4 Cl treated soil (2.6^3.4 mg N g À1 soil day 71 ). The higher mineralization rate was probably due to the presence of readily mineralizable organic substrates in the DSE, accompanied by stimulated microbial and extracellular enzyme activities.The stable organic N compounds in the DSE were slow to mineralize and contributed little to the mineral N pool during the period of the experiment. Nitrification rates during the first 16 days were higher in the NH 4 Cl treated soil (1.7^1.2 mg N g 71 soil day 71 ) compared to the DSE treated soil (0.97^1.5 mg N g 71 soil day 71 ). Soil microbial biomass C and N and extracellular enzyme activities (protease, deaminase and urease) increased after the application of the DSE due to the organic substrates and nutrients applied, but declined with time, probably because of the exhaustion of the readily available substrates. The NH 4 Cl application did not result in any significant increases in microbial biomass C, protease or urease activities due to the lack of carbonaceous materials in the ammonium fertilizer. However, it did increase microbial biomass N and deaminase activity. Significant positive correlations were found between gross N mineralization rate and soil microbial biomass, protease, deaminase and urease activities. Nitrification rate was significantly correlated to biomass N but not to the microbial biomass C or the enzyme activities. Stepwise regression analysis showed that the variations of gross N mineralization rate was best described by the microbial biomass C and N.

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