Responses of Lotus pedunculatus to sulphur fertiliser and defoliation regime in high country

Abstract

The potential for Lotus pedunculatus is greatest in acid soils of our hill and high country. However, its productivity and longevity are sensitive firstly to establishment success, secondly to nutrient supply and thirdly to the grazing management applied by the farmer. We investigated the role of sulphur fertiliser in productivity, and then tested the influence of defoliation regime on production and spread of Lotus after the establishment of high or low plant populations in low pH, high aluminium soils near Millers Flat. The mapping of soil test results to Lotus yield revealed a relationship between soil sulphur content and lotus growth. Sulphur was then applied at two sites (low or high productivity) at three rates (0, 24 or 78 kg S/ha) and measured over three years. To test the impacts of grazing management, defoliation regimes (seasonally to 2 or 5 cm residual height, or once per annum in autumn) were applied to paired plots of high or low initial plants numbers for three years, after a 12-month establishment period. The experimental site, at approximately 1000 masl, had a base vegetation cover of unimproved native tussock, with low soil pH and P (4.8 and 7 respectively) and high available Al (30-40 ppm), after fertiliser application at establishment. Herbage production, plant abundance and rhizome spread were measured. Lotus contributed between 65-85% of the herbage available for grazing (excluding tussocks). Total production ranged between 1900 and 3200 kg DM/ha/annum and was lower when initial plant numbers were lower. The addition of sulphur fertiliser did not alter dry matter yields over three years. Herbage yields were maximised by defoliation to 2 cm height each season or once in autumn. Measurements of the influence of defoliation intensity and initial plant numbers on rhizome spread are pending. The establishment of high plant numbers is essential to lotus stand productivity. Low herbage yields require relatively little nutrient inputs and yields were not affected by additional sulphur fertiliser in the five years after establishment. Impacts of defoliation regime and initial plant numbers will be ready before final paper submission. Subdivision of hill and high-country blocks will improve the longevity of Lotus stands. Ensuring an adequate number of lotus plant establish is key to enabling longevity. Impacts of spelling Lotus for whole growing seasons to aid spread will be included in the paper. Lotus maintains a consistent yield with small fertiliser inputs.