It is well understood that clover plays the key role in New Zealand’s competitive advantage over our European counterparts allowing our farmers to produce lower input cost meat, milk and fibre products for export.
Managing the grass-clover sward to maximise this advantage has been the focus of many studies. The benefits of increasing nitrogen (N) supply via atmospheric fixation of N by rhizobia bacteria in clover root nodules are also well understood. The effect of grazing management and increases in lamb live weights are investigated in this article.
The paper ‘Management of clover in grazed pastures: expectations, limitations and opportunities’ is a lengthy and detailed study and we will break it up into two or three parts to feature in following editions of Country-wide. Fertco’s CloverZone® programme defines the chemical, physical and biological limitations to clover growth and seeks to improve both the vigour and productiveness of clover in the mixed sward.
The Research Grasslands paper ‘Management of clover in grazed pastures: expectations, limitations and opportunities’ identifies some of the limitations to optimising the contribution of clover in complex soil/pasture/animal systems, within the context of the expectations commonly held of clover.
The paper states that it is well known the advantages that clover brings to a mixed pasture, but it is also well known that clover has limitations as a pasture plant. These limitations can lead to inefficiencies in the performance of grass/clover associations. The authors’ aim was to identify some of the limitations to optimising the contribution of clover and look at the role of interactions between the grass and the clover in governing the performance of clover.
‘It is widely accepted that clover is superior to grass, particularly to unfertilised (N) grass, as an animal feed. But it is important to identify factors that limit the realisation of that superiority.
‘Some of the most revealing information comes from studies where equal quantities of clover or N-fertilised grass with similar digestibilities have been fed to animals and fluxes of N within the digestive tract have been measured.
‘These show a relatively small, 15%, advantage to clover in the quantity of (plant plus microbial) protein available for digestion in the small intestine. Data from experiments with sheep (Table 1) show that this difference is due to lower losses of N in the rumen and hence greater efficiency of digestion of protein in animals eating pure clover.
In outdoor studies, intake rates from clover monocultures are seen to be some 1.5 to 2 times those of fertilised grass.
However, outdoors, high intake rates are not synonymous with high total daily intake. There is a limitation on clover benefits because total grazing time on clover is consistently less than on grass. Even when clover constitutes a large proportion of the pasture, and is readily accessible, animals ‘dilute’ the proposed benefits of clover by also eating substantial quantities of grass. There is increasing evidence that there is a nutritional basis for this desire for a mixed diet.
The other limitation to realising the nutritional benefits of clover compared to grass, is the typically low clover content in pastures.
‘The major limitation to clover’s contribution to N input and yield is its current typically low content in pastures (typically <20% of total DM).’
Clover content is also subject to long-term fluctuations, leading to what have become know as ‘good clover years’ and ‘clover crashes’.
This spatial and temporal uncertainty feeds the perception of inadequacy (in the clover germplasm) and risk (in farming practice) that has led to the widespread and sometimes excessive use of mineral N fertiliser in intensive agriculture in the UK and Netherlands.
The argument for using mineral N is gaining strength in New Zealand, and is hard to refute on the basis of research and practical experience with use of N in intensive productive systems. It is still not clear what the optimum clover content of pasture is. The issue is how much can clover content in a pasture be increased to capture the benefi ts of nutritional value, N fixation and yield without compromising the environmental integrity of the grass/clover system.
There is an expectation that an optimal grass/clover balance can be sustained over time, leading to predictable outputs of animal product and N from the system. But expectations of clover performance in mixtures must be realistic.
‘It is appropriate, therefore, to identify factors that limit our ability to harness the advantages of white clover to the maximum, within the context of our expectations of clover performance’.
‘Clearly, then there is great scope for increasing the clover content of pastures from the current low average levels 10-20%. But we should be careful in our expectations of the increases in animal production that might result from raising clover content.
‘Optimistically we can expect ryegrass/white clover mixtures with a high white clover content toapproach the yields of pure grass swards supplied with adequate mineral N’.
The benefits associated with increased clover predominance in the sward and increased productivity relating to greater fixation of atmospheric N are realised by the overall increase in pasture production of grass and clover combined. The increase in intake of higher quality, more nutritious herbage results in better growth rates and greater per hectare performance overall. An increase in clover consumption also supplies more minerals to the animals and improves the protein intake ratio.
The Fertco’s CloverZone® programme works to identify the defines the limitations to your clover growth and to improve both the vigour and productiveness of clover in the mixed sward.