Redefining the production potential of hill pastures using fertiliser nitrogen

Abstract

Farmer perceptions of the productive potential of land influence their attitudes to productivity improvement. Pasture production information has generally been gathered within management systems that were considered feasible at the time. A sheep grazing trial was run over 2 years in southern Hawkes Bay hill country in which a Fer tiliser treatment involving a very high rate of nitrogen (N) fertiliser (400 kg N/ha annually as 8 split dressings of 50 kg N/ha) was applied to blocks with historically low, medium or high fertility. Additional fertiliser P and S was also applied as part of the Fertiliser treatment, however the responses were judged to have been mainly due to the N fertiliser Annual pasture production increased from an average 9.2 t DM/ha in Control areas to 17.1 t DM/ha in Fertiliser treatment areas. Similar responses of 18 to 22 kg DM/kg N fertiliser occurred across the 3 fer tility blocks. Average annual pasture production for the historically high fertility-Fertiliser treatment combination was 19.4 t DM/ha, higher than on most dairy farms. Pasture content of high-fertilityresponsive grasses such as ryegrass increased, at the expense of low-fertility-tolerant grasses such as browntop, legumes such as white clover, and herbaceous weeds. Nitrate leaching measurements suggested annual losses were increased by 25 kg N/ ha or 6% of the N applied. Given present-day cost structures and returns, these results suggest use of higher rates of N fertiliser than is current practice is an economic option for hill farmers. However longterm sustainability of systems receiving such high dressings of fertiliser N r equires further investig ation before such an approach should be adopted as part of commercial practice. Keywords: botanical composition, hill country, New Zealand, nitrate leaching, nitrogen fertiliser, pasture production potential

From there to where? Past, present and future soil fertility management on hill country farms

“…Applying 400 kg N/ha in total (8 applications of 50 kg N/ha) increased annual pasture production from 9.2 tonnes DM/ha to 17.1 tonnes DM/ha averaged across low, medium and high fertility blocks over 2 years of measurement. Significant responses to N fertiliser occurred in all 4 seasons of each year, with highest responses recorded in spring and summer (Lambert et al 2003). The response was similar across the fertility blocks ranging from 7.4 and 7.3 tonnes/ ha for the medium and high fertility blocks and 8.9 tonnes DM/ha for the low fertility block with response efficiencies ranging from 18.2 to 22.3 kg DM/kg N applied (Lambert et al 2003).…”

“…As a result the pastures are severely N deficient and respond well to low rates of N fertiliser after they wet-up in winter (Gillingham et al 2007;2008a). Summer moist hill country pastures, usually with higher legume content, still respond to the use of N fertiliser as was ably demonstrated in a trial at Ballantrae (Lambert et al 2003). Applying 400 kg N/ha in total (8 applications of 50 kg N/ha) increased annual pasture production from 9.2 tonnes DM/ha to 17.1 tonnes DM/ha averaged across low, medium and high fertility blocks over 2 years of measurement.…”

“…Significant responses to N fertiliser occurred in all 4 seasons of each year, with highest responses recorded in spring and summer (Lambert et al 2003). The response was similar across the fertility blocks ranging from 7.4 and 7.3 tonnes/ ha for the medium and high fertility blocks and 8.9 tonnes DM/ha for the low fertility block with response efficiencies ranging from 18.2 to 22.3 kg DM/kg N applied (Lambert et al 2003). Various other authors have previously reported a large range of N responses on sheep-grazed and/or hill country pastures e.g., 14 to 31 kg DM/kg N (Ball et al 1976), 24 to 43 kg DM/kg N (Gillingham et al 1998), 7 to 55 kg DM/kg N (Lambert et al 2012), 13 and 21kg DM/kg N (Ledgard et al 1983), and 10 to 25 kg DM/kg N (Luscombe 1979).…”

Attrition of recommended areas for protection: clearance of ecologically significant vegetation on private land

“…4c). Production from steeper slopes is limited by accessibility and a tendency toward thinner soils and lower fertility, but dramatic increases in pasture production can be achieved through fertilising (Lambert et al 2003).…”

Is nitrogen fertiliser an economic option in tussock hill country?

“…One of the major limiting nutrients in many hill soils is nitrogen (N) (Lambert et al 2003). Experience in the Wise Use of Nitrogen in Hill Country Sustainable Farming Fund programme (www.wisenuse.co.nz) indicates that significant changes in pasture production can be made using high rates of N in moist hill country (Lambert et al 2003). This indicates a potential for N fertiliser to be used as a development tool rather than a tactical feed supplement.…”