Pasture and tussock responses to a single application of nitrogen or a full development process for drier hill country over two years

Abstract

Increasing production from drier hill country to maintain economic viability must be balanced with environmental impacts and the preservation of the tussock landscape. This trial investigated the use of a one-off autumn application of nitrogen (100 kg N/ha) to increase pasture production from drier hill country over subsequent seasons while maintaining the tussock biota. Comparative controls and previously oversown blocks were included. The response to nitrogen in the first winter-spring period was approximately 13 kg DM/ kg N applied with no measurable response occurring thereafter. The oversown block produced around 3200 kg/DM/annum more than the other blocks, as expected in the first two years. The botanical analysis showed that browntop reinvasion of recently oversown pasture was rapid, increasing to a presence of over 50% in three years. Tussocks decreased in size in the nitrogen treated block, but this was possibly due to management practices rather than a response to fertiliser nitrogen. This trial highlights some of the issues that surround the optimal use of nitrogen fertiliser in drier hill country and also documents the invasion of less desirable grasses into the preferred developed pastures. Keywords: Nitrogen, tussocks, oversowing