Development of the pasture management envelope: methods for the analysis, interpretation & application of grazing management experiments

Summary

Guidelines for pasture management need to be based upon a sound understanding of the pasture ecosystem under grazing and the results of experiments interpreted in ways that identify the relevant outcomes and can be easily translated into advisory messages for producers. This project investigated the use of the pasture management envelope which embodies the concept that pastures should be managed within boundaries rather than to fixed points and builds on concepts of 'benchmarks '.

In the envelope a priority is attached to benchmarks and only two are used at anyone time and both lower and upper boundaries is set where management needs to intervene to correct any adverse trends. The boundaries used in the envelope are for key (desirable) species (% dry weight) and for the forage-on-offer (FOOT (green)DM/ha). Secondary boundaries can be set for forage allowance per animal unit to enable estimation of stocking rates. Data from four grazing experiments were used to define boundaries and tested for one independent site. For these pastures it was considered that the lower and upper boundaries for total (desirable) perennial grasses or total legumes, should be 15 to 60%. The FOO boundaries for a phalaris pasture were 1.5 to 3.5 tDM/ha and for cocksfoot and naturalised native grass pastures 1 to 3 tDM/ha. The lower boundaries were considered more important than the upper ones. Each boundary in reality has some flexibility about it. The better management treatments met the boundary conditions for one parameter often, but less so for two parameters, highlighting the problems in expecting producers to meet a list of benchmarks.

The envelope provided a valuable procedure for evaluating treatments and to portray extension messages, but is a sophisticated tool that requires knowledge of pasture assessment and is more appropriate when pastures are in a reasonable state and production and sustainability goals can be set. Further development and use of the envelope is justified. The pasture species composition matrix was developed as a simpler way of describing all the common states that most temperate pastures can exist in. This enabled a concise description of pasture trends under different management practices, from which advisory messages could be deduced and the limitations of some practices identified it should provide a useful vehicle to use with producers to identify their goals in pasture management. Statistical procedures for the analysis of the grazing management experiments were also developed in collaboration with biometricians. Multivariate biplot techniques were used to identify overall treatment effects and the major components influencing a treatment. New splining procedures now enable a general description of time trends in individual pasture components.