G.S. Rajendram1, S.F. Ledgard1, R. Monaghan2, J.W. Penno3, M.S. Sprosen1 and L. Ouyang1 1AgResearch, Ruakura Research Centre, Private Bag 3123, Hamilton 2AgResearch, Invermay, PO Box 50034, Mosgiel 3Dairying Research Corporation, Private Bag 3123, Hamilton Abstract Losses of Ca, Mg, K, Na, nitrate-N, sulphate-S, Cl and inorganic P were determined in intensively grazed dairy pastures at three sites receiving no nitrogen fertiliser. The range of losses for each nutrient in kg/ha/year were 69-144, 10-46, 6-16, 32-79, 21-26, 39-89, 63-123 and <1 respectively. Measurements of leaching losses relative to nutrient inputs in fertiliser, rainfall and drench at DRC Number 2 dairy indicated that leaching of Mg exceeded inputs by approximately 20 kg/ha/year. Leaching losses of the above cations and anions were also measured in dairy cow farmlets at DRC Number 2 dairy which received 0, 200 or 400 kg N/ha/year. The amount of nitrate-N leaching increased with increasing rate of N fertiliser application. This was associated with an increase in leaching of Ca of up to 100%. There was no significant effect on leaching of other cations. Introduction In New Zealand, there have been few studies on the leaching of anions and cations in intensive dairy farming systems. Charge balance needs to be preserved in leaching solutions and therefore a cation will accompany any anion leached. The leaching of anions and cations will be dependent on a number of factors including the amounts and form of nutrients applied in fertiliser, stocking rate, drainage, soil type and extent of previous leaching (McLaren and Cameron, 1990; Scholefield et al., 1993). With the increasing use of N fertiliser on dairy farms over the past 5-10 years, there has been increasing concern about the impact on nitrate leaching to groundwater. Ledgard et al.(1996) showed that increased N fertiliser application on dairy pasture resulted in increased nitrate-N concentrations in groundwater. Leaching of nitrate also results in leaching of associated cations and this has implications to the requirements for nutrients in the farm maintenance fertiliser programme and to the lime requirement (Sinclair et al., 1993). The aim of this study was to determine the amounts of Ca, Mg, Na, K, nitrate-N, sulphate-S, Cl and inorganic P leached from intensively grazed dairy pasture at 3 sites in the absence of N. In addition, nutrient leaching was determined in dairy farmlets at one site receiving 0, 200 or 400 kg N/ha/year. Method Farmlets receiving no nitrogen fertiliser 1. Waikato farmle Cation and anion losses were measured in 1995 in a farmlet at the Dairying Research Corporation (DRC) No. 5 dairy which received no N fertiliser. Soil solution at 1 metre depth was collected using 30 ceramic cup collectors at 2-3 weekly intervals ( Sprosen et al., 1997). Calcium, Mg, Na and K were analysed using atomic absorption spectroscopy, nitrate-N using flow injection autoanalyser, sulphate-S using high pressure ion chromatography, and chloride using uv/vis spectroscopy. The farmlets were rotationally-grazed by dairy cows. The soil type was a moderately-well drained Bruntwood silt loam (Aquic Hapludand) derived from volcanic ash. Drainage was estimated from the volume of water passing through lysimeters (0.4 m diameter by 1 m depth) containing intact soil cores. Data for drainage and nutrient concentrations were used to calculate the amount of nutrients leached. 2. Southland farmlet Leachate from mole and tile drains was collected at frequent intervals from 6 non-N-fertilised paddocks (Monaghan, unpublished) in 1996 and was analysed for anions and cations as described above. Inorganic P was analysed using uv/vis spectroscopy. The paddocks were rotationally grazed by cattle. The soil was a Fleming silt loam which is a naturally poorly-drained sedimentary soil. DRC No. 2 dairy, Hamilton Cation and anion losses were measured in 1995 and 1996 in a farmlet at the DRC No. 2 dairy near Hamilton which received no N fertiliser. Soil solution at 1 metre depth was collected using 30 ceramic cup collectors at 2-3 weekly intervals (Ledgard et al., 1996). The soil was a free-draining Silverdale silt loam (mottled orthic brown soil). Cations and anions in leachate were measured as above. Farmlets receiving nitrogen fertiliser DRC No. 2 dairy, Hamilton Measurements were made of anion and cation leaching in farmlets at the DRC No. 2 dairy near Hamilton. Treatments received 0, 200 or 400 kg N/ha/year as urea in 8-10 split applications throughout the year (Table 1). Table 1: Nitrogen fertiliser applied as urea to farmlets at DRC No. 2 dairy Hamilton (Penno et al., 1996). Leachate from the free-draining Silverdale silt loam (mottled orthic brown soil) was collected using ceramic cup samplers located at 1 metre depth (30 samplers per treatment). Groundwater was also sampled using piezometers (3 per treatment; to a depth of 6 m) located within grazed paddocks of each treatment. The solutions were analysed as above for cations and anions. Phosphate in groundwater was also analysed. The extent of water drainage from each treatment was measured using lysimeters (0.4 m diameter by 1 m deep) containing undisturbed soil cores. The nutrient inputs via fertiliser and rainfall (which were measured) are summarised in Table 2. Fertiliser inputs were muriate of potash applied at 100 kg/ha/year and superphosphate applied at 600 kg/ha/year. Lime was applied to the farmlets at commencement of the trial in 1993. Results Farmlets receiving no N fertiliser High losses of calcium, magnesium, sodium, nitrate-N, sulphate-S, and chloride were observed for the farmlets at No. 2 dairy Hamilton, Waikato and Southland (Table 3). There were lower losses of potassium and inorganic P (all < 1 kg Pi/ha). At each site, the annual amounts leached from the grazed pasture receiving no N fertiliser were in the order Ca > Na > Mg > K and for the anions were in the order Cl > sulphate-S > nitrate-N. At No. 2 dairy, the amounts leached were higher in 1996 than 1995, which coincided with greater drainage. The amounts of calcium and nitrate-N leaching increased ( p< .001) with increasing rate of N fertiliser application at DRC No. 2 dairy during 1996 (Fig. 1). However, there was no effect of N
