VSN International / Case Studies / Strategic Grazing using Reml

Strategic Grazing using Reml

Farming strategies started way back with crop rotation which helped to prevent the soil being drained of all nutrients through over farming by one plant. Times have moved on as technology does and we’ve entered a more complex world of pesticides, herbicides, fertiliser and new crop development. As the world’s population grows the demand for food and agricultural products will increase; but it isn’t as simple as “grow more”. There is little doubt that the world needs to get smarter with its farming and farming techniques, and this needs to cover all aspects of farming, from land management to plant types.  I recently came across some research from Australia that is looking at how different grazing systems affected the yield and quality of a particular grass in the Western District of Victoria. Interestingly the basis of this project is not on new plants, or new herbicides and pesticides, it’s more about finding out the most suitable plant with the most suitable grazing system. Margaret Raeside, a PhD student at Charles Sturt University, is evaluating the benefits of a summer growing variety of tall fescue. This specific study is part of a research project run by EverGraze, with Charles Sturt University and the Victorian Department of Primary Industries, that aims to boost profits for wool and livestock producers, whilst lowering groundwater recharge and soil salinity.

The Western District of Victoria is known for its heavy clay soils, that are prone to short periods of waterlogging for 2-3 months a year in the Winter; but with the right pasture species livestock producers could increase pasture production during the Summer by utilising this stored soil moisture. Additionally a species that can use out of season rainfall and moisture stored in the soil, would reduce groundwater recharge. One such plant is Summer-active tall fescue.

The experiment, which began in November 2004 with the establishment of the grass, is taking place at the DPI EverGraze research site at Hamilton;  4 grazing system treatments were imposed in a randomised design in September 2006. Since then the plots have been grazed at different levels and herbage mass measured monthly to calculate herbage accumulation.

GenStat’s REML technique was used to model the repeated measurements over time.

Coopworth sheep

This enabled seasonal changes in pasture productivity and quality to be detected, and indicated how the plant responds to climatic events, such as the summer rainfall that is a common characteristic of the research site. Stocking rate, and major husbandry practises, such as lambing and calving, could then be timed to coincide with pasture availability. Within each time period, GenStat was used to determine the effects of grazing treatment on pasture persistence, productivity and quality.  Grazing management was then adjusted, based on the results of the GenStat analysis, to achieve maximum consumption of high quality pasture by livestock, whilst also ensuring the long term survival of the pasture.  Throughout this research, efforts were made to reduce error, and increase the accuracy of the results.  This was achieved by using repeated measurements from fixed quadrants, and also by using GenStat’s graphics capabilities to generate residual plots, which were used to check the normality of the data, and, where needed, impose data transformations.

The study found that the accumulation rate and nutritional value of the Summer-active tall fescue are closely related with its growing conditions. Specific grazing systems and the environmental conditions had an effect on the herbage accumulation and nutritional value. Research, such as Margaret’s is vital in being able to provide sound advice and reliable observations to landowners, and because GenStat was originally developed by statisticians working in agricultural research, it is the most suitable data analysis tool for agricultural research. Couple GenStat’s understanding of the agricultural researchers issues with the reliable and proven statistics, and ethics of good statistical practice and you know your analysis results can be trusted.

Details of Margaret’s project and more information is available at EverGraze. An action sheet based on Margaret’s work on summer active Tall Fescue is here.


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