Pasture responses to phosphorus and nitrogen fertilisers on east coast hill country: 3. Production from steep slopes

Abstract

Aseries of trials was established in 2000, and measured until 2002, down the east coast of New Zealand on seven farms with contrasting amounts of spring-summer rainfall and resultant pasture growth. The aim was to evaluate the pattern of pasture responses to a range of nitrogen (N) fertiliser rates and associated soil phosphorus (P) levels generated by a range of P fertiliser treatments. Small plots excluded from grazing were established on steep (about 20 degrees slope) sites containing pastures that had been established for many years. Each of these steep sites was located within a hill paddock containing similar areas with a wide variety of slopes ranging from near flat to steep. Pasture production was measured approximately monthly (less frequently in seasons of slower growth), and soil was sampled for soil Olsen P test in mid spring each year. 90 kg N ha -1 ) were measured from three northern sites, whereas lower responses were recorded at the southern sites, and especially at Moeraki (3.7 kg DM kg -1 N applied). This may be partly explained by the lower temperatures in early spring at those sites. There was no pasture response over the late spring-autumn period in the North Island. However responses were measured at Moeraki in the South Island. There was little change in the average pasture response (kg DM kg -1 N fertiliser applied) to N fertiliser applied at 30 kg N ha -1 and at 90 kg N ha -1 at each site. This was in contrast to responses measured at the same locations on more gentle sloping sites where the average response declined as the rate of fertiliser N applied increased. Pasture responses in early spring to increase in soil Olsen P test were most pronounced on sites such as Wairoa and Wairarapa, with higher than average pasture clover content, and in years where the clover component was greatest. Some pasture responses to increase in soil Olsen P test also occurred over the late spring-autumn period, generally where there was significant clover content. Conclusions from these trials, together with those earlier reported, show that the initial grass:clover composition of the pasture, whether on easy or steep slopes, was able to be modified by both N fertiliser application, and by increasing soil Olsen P test, and was also a determining factor in the responses measured.

Pasture responses to phosphorus and nitrogen fertilisers on east coast hill country: 2. Clover and grass production from easy slopes

“…The same conclusion was reached by Gillingham et al (1998) as a result of earlier trials on summ er dry hill country near Waipawa in Hawke's Bay.…”

“…Trial management may therefore impose a greater than desirable amount of shading on clovers present, but this would be similar to that encountered on many rotationally grazed hill farms. Gillingham et al (1998) reported a reduction in clover content of hill pastures that had received N fertiliser and were rotationally grazed by ewes and cattle.…”

Simple models of carbon and nitrogen cycling in New Zealand hill country pastures: exploring impacts of intensification on soil C and N pools

“…The use of N fertiliser in hill country farming has increased considerably in recent years (MacLeod & Moller 2006). A range of N fertiliser responses of 1Á33 kg DM/ kg N have been reported in hill pastures (Luscombe 1980;Ball & Field 1982;Lambert et al 1986;Clark & Lambert 1989;Gillingham et al 1998;Blennerhassett 2002;Gillingham et al 2007Gillingham et al , 2008a. Factors affecting the magnitude of response include location (Ball & Field 1982;Gillingham et al 2008aGillingham et al , 2008b, fertiliser application rate Gillingham et al 2007Gillingham et al , 2008aGillingham et al , 2008b, season, slope (Ledgard et al 1983;Gillingham et al 1998;Blennerhassett 2002;Gillingham et al 2003), aspect (Blennerhassett 2002;Gillingham et al 2003) and pasture species composition (Ledgard et al 1982;Rumball 1991).…”

Developing variable rate application technology: Economic impact for farm owners and topdressing operators

“…Although considerable information exists about the relationship between the application of phosphorus fertiliser, pasture growth and the influence of topography (Lambert et al 1983(Lambert et al ,2000Gillingham et al 1998;Lopez et al 2003;Dodd et al 2004), up until now we have lacked the mechanism to apply variable rates of fertiliser to match the potential of the land. A variable rate control system designed by the New Zealand Centre for Precision Agriculture, Massey University in conjunction with Wanganui Aerowork Ltd has been developed, and commercial trials using this system have resulted in a ground resolution of 18 × 18 m. Figures such as 15-20 kg superphosphate SU -1 yr-1 wintered have been used as a broad recommendation (Morton & Roberts 1999); however the within-field variability of hillcountry pasture production is often overlooked.…”