Nutrient leaching under intensive sheep and beef grazing : Master of Philosophy in Animal Science, School of Agriculture and Environment, Massey University, New Zealand
The sheep and beef industry plays a vital role in the New Zealand economy, but there is growing concern about water quality in the pastoral farming systems. To address this issue, regional councils are implementing restrictions on nitrate leaching rates to improve water quality. Nitrate leaching is influenced by factors such as plant uptake rate, rainfall, soil type, and texture, as well as the stocking rate of grazing animals. However, there is a lack of information on nitrate leaching from sheep and beef farms, particularly in the context of winter cropping options like kale (Brassica oleracea) and Turnips (Brassica rapa subsp. rapa). Additionally, the potential of planting Italian ryegrass as a cover crop mixed with brassica to reduce nitrate leaching has not been thoroughly explored. This study aims to compare nitrate leaching under sheep and beef cattle which are grazing perennial ryegrass/white clover, as well as investigate whether mixing Italian ryegrass with brassica can mitigate nitrate leaching. Furthermore, the study will compare the measured rates of nitrate leaching with predicted values using Overseer and a model that simulates N dynamics in urine patches. An experiment has been established in twenty hydrologically isolated plots at Massey University’s Keeble farm for the year 2022. Each plot contains an isolated mole and pipe drainage system to monitor drainage water and assess nitrate leaching. There were five replicates of four treatments: sheep grazing perennial ryegrass/white clover, sheep grazing turnips/Italian ryegrass, sheep grazing kale, and cattle grazing perennial ryegrass/white clover. Measured leaching losses under all treatments were small and there was no significant difference between the nitrate leaching flux of any of the treatments. While Overseer estimates of nitrate leaching were greater than the observed values, they also suggested that there should be no significant difference in leaching rates from the plots Overseer was used to explore likely leaching rates at greater stocking rates. These results suggested that under more intensive farm systems (18 SU/ha), leaching rates under cattle are likely to be greater than under sheep. This difference can be explained by reference to the distribution pattern of urine-N of sheep verse cattle: sheep spread the urine-N load over a greater area. The findings of this study are evidence of the advantages of dry stock farming, particularly sheep, to water quality.
Networked Digital Library of Theses and Dissertations