As concerns grow across much of Scotland about the dry conditions, we look to the considerations that go into managing grass and forage crops during periods of stress. The graph above from GrassCheck GB week commencing 6th June highlights the predicted impact of a lack of rain on grass growth over the coming weeks and will no doubt have an effect on animal growth rates and winter forage stocks.
Whilst we cannot control the weather it is hard to overlook the fact that periods of very dry weather are becoming more common, with the timing of that period varying year to year and region to region. This poses significant challenges for grass growth and quality but there are few factors which we can influence to try and minimise the impact before the inevitable rain arrives.
- As grass moves out of the vegetative phase and into a reproductive state animals can sense the increased lignin in the plant and will actively seek out fresher, green leaves. Not only is the quality of the grass reduced but growth is also slowing down. Management to overcome this can include topping of pastures to remove the stemmy material and reset residuals or the use of rotational grazing to reduce the amount of selective grazing and give those developing leaves time to grow rather than being nipped off as animals look for vegetative growth. We can also adapt the class of stock grazing those longer pastures using dry cows or ewes to tidy them up instead of compromising the performance of growing animals.
- Under dry conditions grass plants are under stress so minimising other sources of stress such as low soil pH, P and K levels, compaction, or competition from overpowering weeds such as docks will help to reduce the accumulative effect of multiple stresses. Potash has a significant role to play in helping plants to be more drought tolerant through the regulation of stomata opening. Low potassium levels in plants results in the stomata reacting too slowly leading to water vapour loss and reduced photosynthesis. Again, compounding the issue of a lack of water. You can read more at Potassium and drought tolerance - Potash Development Association (PDA)
- Maintaining Nitrogen supply, whilst the immediate reaction may be to hold off on applications of Nitrogen until there is rain forecast a lack of Nitrogen available to the grass plant can form another element of stress. Reduced applications of products such as ammonium nitrate which are at lower risk of volatilisation will be available to help that plant to recover more quickly once there is sufficient moisture for plant uptake. Holding off on applications can result in a delayed reaction in the availability of Nitrogen to the plant however if there is residual nitrogen built up that has not been used further applications will not be needed. Grass MUST still be growing to uptake this Nitrogen, if grass is visibly burning you will have to wait for sufficient rain.
- Soils which are compacted have larger soil particles with uneven pore spaces between soil particles and this lack of space and uniformity impacts the flow of water both down through the soil profile but also from the groundwater up into plant root spaces. Compacted soils essentially exasperate the issue of a lack of water due to its reduced ability to move through the soil. Regular investigation of soils using the visual evaluation of soil structure (VESS) guide will help identify any problem fields and dictate the appropriate mode of action.
- If topping stemmy grass or cutting silage, consider raising the height of mower or topper to leave more grass cover and protect the soil from exposure to sun to help retain moisture.
- When grass is grazed below the target height of 4-5cm the plant must use more energy from its root reserves to produce leaf area to then photosynthesise, slowing down recovery and reducing growth. This also places significant stress on the plant. Moving stock off fields at that target residual will ensure the plant is given time to recover.
- If you have areas of grass which do not recover from the dry conditions consider over sowing these with new grass to maintain a competitive sward of productive grasses and keep weeds out.
In the longer term we can look at our systems as a whole and see where different plant species or the use of forage crops can help us become more resilient during these periods of slow growth. Legumes such as red and white clover and herbs such as chicory have deeper root structures in comparison to grass plants and can tolerate growing in higher temperatures. In the correct conditions legumes can also help to reduce our reliance on artificial Nitrogen as it will fix its own Nitrogen from the atmosphere and convert this to a plant available form of nitrate – reducing costs and potential losses of gases to the atmosphere. You can read more and catch up on some videos and podcasts with farmers successfully integrating multi species swards into their farming systems at www.fas.scot.
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