Phosphorus (P) is one of the most important mineral nutrients in agricultural systems, and along with nitrogen (N), is generally the most limiting nutrient for plant production. Farming systems have intensified greatly over time, and in recent years it has become apparent that the concomitant increase in losses of N and P from agricultural land is having a serious detrimental effect on water quality and the environment. The last two decades have seen a marked increase in research into the issues surrounding diffuse losses of P to surface and ground water. This paper reviews this research, examining the issue of P forms in runoff, and highlighting the exceptions to some generally held assumptions about land use and P transport. In particular the review focuses on P losses associated with recent P fertilizer application, as opposed to organic manures, both on the amounts and the forms of P in runoff water. The effects of the physicochemical characteristics of different forms of P fertilizer are explored, particularly in relation to water solubility. Various means of mitigating the risk of loss of P are discussed. It is argued that the influence of recent fertilizer applications is an under-researched area, yet may offer the most readily applicable opportunity to mitigate P losses by land users. This review highlights and discusses some options that have recently become available that may make a significant contribution to the task of sustainable management of nutrient losses from agriculture.

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Ammoniacal nitrogen (ammonia and ammonium) in agricultural wastewaters can promote eutrophication of receiving waters and be potentially toxic to fish and other aquatic life. Zeolites, which are hydrated aluminum-silicate minerals, have an affinity for ammonium ions (NH 4 + ) and are, therefore, potentially useful in removing this contaminant from wastewaters. The major objectives of this study were to evaluate the capacity of two natural New Zealand zeolites (clinoptilolite and mordenite) to remove NH 4 + from a range of wastewaters under both batch and flowthrough conditions. Effects of two zeolite particle size ranges (0.25-0.50 mm and 2.0-2.83 mm) on NH 4 + removal performance were also investigated. Results obtained from the batch adsorption experiments indicated that both zeolites tested, regardless of their particle sizes, were equally effective (87-98%) -3 of wastewater throughput, which equates up to 5.8-6.5 g NH 4 -N kg -1 zeolite. In contrast, at a faster loading flow rate (15.9 mm min -1 ), the breakthrough was almost immediate (1 BV) for coarse zeolites and after 22 BVs for fine zeolite. The NH 4 + breakthrough capacity for fine mordenite was 2.0-4.4 g NH 4 -N kg -1 zeolite. Fine zeolites were more effective than coarse zeolites in removing wastewater NH 4 + (95% and 55% removal, respectively), even after receiving 64 BV of wastewater.

A simulated rainfall study carried out as part of a larger grazing experiment was conducted to investigate the effects of a 2-3 day cattle-treading event in winter on soil physical properties and contaminant (sediment and nutrient) runoff in topographically variable hill land. Measurements were made on two land zones: easy contoured ridges and gullies (15-24° slope) and steep inter-track land (28-39° slope). Simulated rainfall was applied to 16 plots (0.5 m 2 ) with a range of treading damage for each land zone within 14 days of the treading event. Simulated rainfall was repeated on the same plots in the following summer and winter to assess the recovery of soil from treading damage. A97034 Received 28 April 1997; accepted 22 January 1998Treading damage reduced water infiltration rate, particularly in the steep zone. It also caused a significant increase in the transport of suspended solids (SS), total Kjeldahl nitrogen (TKN), and total phosphorus (TP) from the plots during simulated runoff. On the steep inter-track zone, damaged areas had a 46% lower infiltration rate, and runoff from these areas contained on average 87% more sediment, and 89% more N and 94% more P compared with undamaged areas. These effects had disappeared six months later. The rainfall simulation and soil physical studies show that a 2-3 day winter treading event may increase soil bulk density, reduce soil macroporosity and total porosity, and lead to a decrease in the water infiltration rate and an increase in contaminant runoff.

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To determine the effects of soil amendments (lime or ammonium-sorbed zeolite) on emissions of nitrous oxide (N2O) and dinitrogen (N2) gases from pasture and wetland soils, a 90-day incubation experiment was conducted under controlled moisture and temperature conditions. Soil samples (0–0.10 m soil depth) collected from pasture and adjacent wetland sites were treated with 2 nitrogen (N) sources (cow urine or urea) at 200 kg N/ha with and without added soil amendments using 10-L plastic containers and then incubated at 25°C. Subsoil samples were taken out at different intervals to measure gaseous emissions of N2O and N2 using the acetylene (C2H2) inhibition method, ammonium (NH4+), nitrate (NO3–), soluble organic C, and pH. The anaerobic conditions (81% water-filled pore space) in wetland soils precluded nitrification, and therefore no increase in NO3–, N2O, or N2 was observed during the 90-day incubation period. In the pasture soil, the application of urine, urea, and soil amendments significantly affected daily and total N2O and N2 emissions and their ratios over a 90-day incubation period. Total N2O emission from urea-treated soil (48 kg N2O-N/ha) was significantly higher than from urine-treated soil (39 kg N2O-N/ha) and the control soil (4.5 kg N2O-N/ha). The application of zeolite significantly reduced N2O emissions from urea and urine-treated soils by 45% and 33%, respectively, due to the sorption of NH4+ by zeolite. Liming had minor effect on N2O emission. However, when lime was applied with zeolite, a significant reduction in N2O emission was observed. Lime application alone was found to increase N2 emissions in urine and urea treated soils by 46% and 35%, respectively, and thereby lower N2O : N2 ratios. The results indicate that zeolite reduced N2O emission while lime increased N2 emissions and lowered N2O : N2 ratios, and warranting further attention for mitigation of N2O.

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A grazing experiment on aLismore stony silt loam in mid Canterbury spanning a 34-year period has demonstrated the importance of both phosphorus (P) and sulphur (S) fertilisers for the development and maintenance of irrigated ryegrassclover pastures, especially during spring and summer growth periods. In the initial stage of pasture development, the absence of P or S fertiliser inputs can lead to a severe reduction in pasture production and a deterioration of the pasture sward towards weeds and weed grasses at the expense of high quality ryegrass and clover species. Superphosphate applied at rates of 21-24 kg/ha per year is sufficient to satisfy phosphate maintenance requirements for irrigated pastures. However, the S content in superphosphate applied at these rates exceeds pasture S requirements. Spring application of sulphatecontaining phosphatic fertilisers which aims to provide P at a maintenance rate of21-24 kg P/ha per year is also sufficient for pasture S requirements if these fertilisers have a ratio of StoP content of about 0.8: 1. A short-term application of superphosphate for 6 years even at rates well above the maintenance P and S requirements was unable to safeguard pastures against yield reduction or pasture deterioration towards weeds and weed grasses even in the first growing season after superphosphate was Received 18 October 1988; accepted 10 February 1989 discontinued. Superphosphate applications over several years, however, can build up soil P and S reserves which may contribute significantly to plants. Under this situation, the residual value of previous applications may be able to maintain pasture production and high quality herbage species without any reduction for a longer period than that observed under short-term applications. Since soil organic S as well as organic and inorganic P can accumulate under grazed pastures, especially after prolonged annual applications of superphosphate, the contribution of these reserves to pastures should be considered in conjunction with soil phosphate and sulphate tests when assessing pasture requirements for these two nutrients.