Small changes in grazing management can reap big benefits.
In the current tight times many dairy farmers will be focusing on gaining the best return from their investments using the resources they have available. One investment most farmers have already made is sowing pastures. The management of these pastures will impact the return on this investment. Two things that can increase this return are grazing management and nitrogen.
Many farmers have heard about leaf stage grazing, however it is important to get the basics right, especially in tight times, as small changes can result in big benefits.
The aim of good grazing management is to balance the requirements of the pasture and herd. Deferring grazing between the two- to three-leaf stage allows pasture to reach its potential production. By the two-leaf stage the tiller has restored its energy reserves required to regrow after the last grazing. Allowing the tiller to reach the three-leaf stage before grazing can be a bonus as the third leaf is an extra 30–40 per cent larger than the second leaf — though if we go beyond this the first leaf begins to die, increasing wastage.
In spring you may reach canopy closure before the two-leaf stage. If this occurs, graze before or on canopy closure, because leaving it past canopy closure will lead to death and decay, thus increasing wastage. Canopy closure is the point when no light is able to reach the bottom of the canopy and can be identified when we are no longer able to see the ground through the canopy of the plant.
Aim to leave a post-grazing residual of 4–6 cm between clumps, because this is where the tiller stores its energy or ‘fuel’ to re-grow. Grazing below 4 cm will reduce the amount of energy reserves available, resulting in smaller tillers, slower regrowth and less pasture at the next grazing, while grazing above 6 cm has no benefit to growth and increases pasture wastage.
With low temperatures and short day length during winter, leaf appearance rate slows. This means the rotation length needs to be lengthened so the pastures continue to reach the two- to three-leaf stage target. As we head into spring our days become warmer and longer, accelerating leaf appearance rate and resulting in a shortening rotation. Remember to keep an eye on the leaf stage of the pasture you are offering to the herd each day to see if you are reaching your target leaf stage and not shortening your rotation too soon while maintaining post-grazing residuals.
Remember, lengthening or shortening rotation length is about reaching the desired leaf stage. Post-grazing residuals are a measure of supplementary feeding level with higher residuals indicating over-feeding and low residuals indicating under-feeding.
Nitrogen fertiliser is useful and, used strategically, can boost pasture production and fill feed gaps. When making decisions, base them on the potential response rate in conjunction with your feed budget and feed requirements. Ensuring the extra pasture grown is consumed will maximise the return on this investment.
The use of nitrogen does not increase the rate of leaf appearance but increases the size of the leaf, increasing the volume of feed available to be grazed. This can lead to the occurrence of canopy closure before the three-leaf stage is reached, particularly in tetraploid varieties. It is best to graze at the point of canopy closure than to allow death and decay to occur which will lead to feed wastage.
The cooler temperatures in late winter result in a lower response to nitrogen than in spring or autumn, though this does not mean it is not cost-effective. Often during winter supplement feed prices are higher and quality feed is scarcer, making nitrogen a viable option. If soil temperatures drop below 4°C response rates will be very low. A table of responses you could expect can be found under the tools tab at http://www.nitrogen.unimelb.edu.au/Index.htm
Urea continues to be the cheapest source of nitrogen. There is no difference in the response rates of different forms of nitrogen (for example, urea verses DAP) unless there is another nutritional deficiency. The best response will come from those paddocks with few other limiting factors. Paddocks with better species composition, high density, good fertility (P, K and S) and limited weeds with no waterlogging will respond best.
Nitrogen should be applied two to three days either side of grazing at a rate of 25 to 50 kg N/ha (about 50 to 100 kg urea/ha) to allow the plant to fully utilise the nitrogen for growth. Applying earlier than three days before grazing increases the risk of nitrates and reduces the potential response from the nitrogen applied. Applying less than 25 kg N/ha often results in unpredictable responses, while applying above 50 kg N/ha can result in a reduced response per kilogram of nitrogen applied. Combining this with grazing at the two- to three-leaf stage will maximise pasture growth.
A tool available to help calculate this point for your situation is the Dairy Nitrogen Fertiliser Advisor: http://vro.agriculture.vic.gov.au/dpi/vro/vrosite.nsf/pages/nitrogen-advisor
— Sarah Brown, dairy extension officer, Agriculture Victoria, Tatura