Pasture responses to phosphorus and nitrogen fertilisers on East Coast hill country: Total production from easy slopes

Abstract

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.

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

“…This was quite different from the "diminishing returns" effect of increasing N fertiliser rate on pasture response recorded on flatter sites in the associated trial series (Gillingham et al 2007), and in results published for ryegrass:clover pastures (Ball & Field 1982;O'Connor 1982). This suggested that the soil on steep slopes was more deficient in available nitrate than was the soil on easier slopes.…”

“…comm. ), and, except for the Wairoa and Wairarapa locations tended to be slightly lower than those measured on adjacent flatter slopes at the same time (Gillingham et al 2007). The values measured in Pumice soil at Wairoa (0.64 mg kg -1 ) and the value Table 2 Statistical significance of N fertiliser and Olsen soil P effects on total pasture dry matter production (kg Dm ha -1 ) in the early spring season (Jul-oct) from 2000 to 2002 at each site.…”

“…The relatively moist, south facing, Wairoa site had pasture with the highest proportions of clover, and the least variability between years, reflecting the higher and more reliable summer rainfall at this site (Gillingham et al 2007; Table 1). At other sites the clover content was lower and much more variable Table 3 Pasture clover content (estimated % contribution to total dry matter (Dm) production) in early spring and in late spring-autumn periods of each year at each of the zero and 90 kg ha -1 rates of N fertiliser, and for the Control and high P treatments only.…”

“…mean annual rainfall ranged from 474 mm (marlborough) to 1348 mm (Wairoa). Farms received an average spring rainfall that comprised 18-33% of the annual total, and summer rainfall which comprised 20-32% of the annual total (Gillingham et al 2007).…”

“…in 2000, seven trial sites were selected (Gillingham et al 2007) on established pasture within sheep and beef hill farms near Wairoa, Napier (Puketapu), Waipawa, Waipukurau (Wallingford), masterton (Wairarapa), Seddon (marlborough) and moeraki in North otago to represent a range in annual rainfall and associated pasture growth conditions. mean annual rainfall ranged from 474 mm (marlborough) to 1348 mm (Wairoa).…”