A long-established, moderately steep hill pasture was visually mapped into five strata (A to E) according to occurrence, colour, and vigour of pasture species and distribution density of obvious urine patches.An!,lUal pasture production and major nutrient concentrations of the pasture, except magneSIUm, decreased markedly from stratum A to stratum E. Phosphorus and potassium soil tests were distinctly higher in stratum A than in the remainder of the paddock.From the measured nutrient uptake in pasture and from dung counts carried out on each stratum, it was estimated that large quantities of P, K, and N were transferred into camp areas, mostly from the least productive two-thirds of the paddock.Because of the irregular distributi.on of the. strata. it is !'lot practic::ble to compensate fully for the observed transfer of nutnents by dlfferentJal aenal topdressmg; but phosphatic topdressing of 10 percent of this paddock could probably be omitted without measurably affecting total production.The significance of the five strata in soil sampling and the incidence and correction of potassium deficiency are discussed.
New Zealand pastoral farm land is intensively grazed and receives predominantly single superphosphate fertilizer. Resource managers and policymakers are concerned about the effects of such land use on P enrichment of waterways and lakes. This paper reviews New Zealand research on the effects of agricultural land use on P losses in water runoff and highlights priorities for management and future research. Diffuse agricultural sources contribute about 91% of total P entering fresh waters annually, with 0.11 to 1.67 kg P ha−1 yr−1 being removed, mostly in particulate forms. Despite a number of studies showing good site‐specific correlation, no widely applicable soil test method for estimating runoff dissolved P concentration has been found. The effects of (i) fertilizer application in increasing surface runoff P concentrations (ii) riparian areas in both source and control roles, and (iii) subsurface drainage, in reducing losses of P in surface runoff from pasture land, are reported. A catchment scale simulation model, Basin New Zealand (BNZ), for intensively grazed pastures, has been produced based on CREAMS (chemicals, runoff, and erosion from agricultural management systems). This model adequately predicts P loss at the field scale but is less reliable at the catchment scale, which indicates differences in predominant P and sediment sources at the two scales. Corrective management has alleviated eutrophication problems in some lakes and waterways; however better information is yet required to understand, model, and manage the more insidious losses of P to waterways from New Zealand farm land.
A series of small, mowed plots, excluded from grazing, were established on flat to easy sloping (up to 15°) pastures on farms from Wairoa (northern Hawke's Bay) to Moeraki (North Otago) with contrasting degrees of spring, summer and autumn dryness, to evaluate the pattern of pasture responses to a range of nitrogen (N) fertiliser rates, and associated soil phosphorus (P) levels. Mean annual rainfall ranged from 474 (Marlborough) to 1348 mm (Wairoa) with all farms having an associated range in spring/summer/autumn rainfall. In mid-late winter 2000, fertiliser P and N were applied at 0, 30, 60 or 90 kg ha -1 in a completely randomised design with incomplete replication. In winter 2001 and 2002 the rates of N fertiliser (urea) treatments were repeated. The application of P fertiliser (triple super) varied between treatments, sites and years in an attempt to generate and stabilise a range of soil P tests at each site. The rates of P applied in were based on the soil Olsen P test in the previous spring. The pasture response to N fertiliser differed between the early spring (August-October) and late spring-autumn seasons. The pasture response in early spring to N fertiliser ranged from 1.58 kg DM kgr 1 N in Marlborough to 17.9 kg DM kg -1 N fertiliser at Wairoa. Conversely, at almost all sites, there was a negative pasture response in late spring-autumn to increasing rate of N fertiliser. The net difference between the positive pasture responses to fertiliser N in early spring and the negative effects in late spring-autumn showed a positive net response over the total season. The overall average for all sites was 12.4 kg DM kg -1 N response at the 30 kg N ha -1 rate, and 7.6 kg DM kg -1 N fertiliser at the 90 kg N ha -1 rate. The relative pasture responses at most sites to increasing soil P status was similar in both the early spring, and in the late spring-autumn seasons. Asymptotic regression relationships (Mitscherlich type), derived for data from each of the Wairoa, Puketapu, Waipawa, Wallingford and Moeraki sites suggested that near peak responses were obtained at Olsen soil P test of 20.
Simulation models of soil water balance for flat land are not applicable to hill soils, principally because on the latter sites significant runoff can occur before the soil reaches field capacity. Part of the data from regular measurements of topsoil (0-75 mm depth) moisture content over a 3-year period on the north aspect of a steepland yellow-brown earth soil was used to construct a simulation model which described changes in soil moisture to 150 mm depth during the year. Similar data collected on a south aspect of the soil and also on north and south aspects of a yellowbrown loam hill soil were used to evaluate the model. A 4-layer model was developed in which the rate of soil rewetting was empirically limited according to soil moisture content and evapotranspiration rate was primarily soil-controlled. Predicted topsoil moisture levels provided similar, but generally lower values compared to actual levels especially during the summer to late winter period: The greater discrepancy during early spring could be attributed to the role of unaccounted-for subsurface flow downslope and/or rapid infiltration bypassing surface layers but contributing to actual moisture levels below the soil surface. Despite these limitations the modelling exercise enabled 2 major conclusions to be drawn which were not previously apparent. First, because of the low storage capacity of these soils the availability of moisture to pasture was highly dependent on rewetting frequency rather than total rainfall and, second, as a result of this, probably less than 50% of the total annual rainfall was involved in replenishing soil moisture at plantavailable depths.
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