The primary aim is to examine the consequences for livestock producers of adopting a reduced output strategy based on the substitution of legumes for N fertiliser. Secondarily the work aims a) to test the use of a simple simulation model to obtain an increase in herbage utilization efficiency and b) to identify the factors affecting the ecological stability of grass/clover associations.
Linked research into clover herbage interactions was carried out in Ireland, France, Italy and United Kingdom. In the United Kingdom French concerted action a model for lucerne (Medicago sativa) growth was developed under experimental conditions, considering net crop photosynthesis, the partitioning of assimilates and the respiratory costs of biological nitrogen fixation.
The French Italian multilocation trials showed that, due to a greater yielding capacity and stability in yield, combinations of grasses and legumes always result in better performance than the corresponding monocultures. This also applied to lucerne in combination with cocksfoot (Dactylis glomerata) while formerly lucerne was considered not to be able to survive in a combination with any grass species.
The Irish contribution included the grazing animal and the development of a grazing management system that optimizes sward conditions for grass legume pastures and maximizes animal output by improving utilization of pasture.
It was found that a grass clover sward without nitrogen had a carrying capacity 70% of that of a grass sward with high rates of mineral nitrogen fertilizer. This comparison not only reflects the difference in dry matter production but also includes differences in feed value between the systems. The financial margin of animal husbandry on grass clover swards compared to high rates of mineral nitrogen at current prices was calculated at 89%; financial equilibrium will be attained at doubling of nitrogen fertilizer prices.
Rotational grazing trial with 4 treatments i.e. grass/clover sward and grass sward receiving 250 N kg ha-1 ann-1, each grazed at 2 stocking rates by steers. Utilization of herbage is maximised by grazing all paddocks to 50mm. In a 20 day rotation any paddock not required for grazing is cut as silage and used as a strategic reserve for use as a supplement in periods of feed deficit. Simulation model is used to monitor continuously the level of herbage available in each treatment to provide advance alerts of feed surplus or deficit. In selected paddocks of the grass/clover sward the distribution of clover relative to grass and of each species relative to levels of physical environmental factors is examined.