Management of cereal root systems

Summary

Background

At present we do not know how to manage root systems in the way that we can manipulate canopies. We know that management decisions can affect cereal roots but in many cases do not know what the result is for yield and quality. The project was a desk study and consultation to find out what is known already so that future research can be appropriately targeted.

Situations where rooting can limit yield

Poor rooting can limit growth due to low uptake of water or nutrients or by increasing the risk of lodging. Root systems respond dynamically to soil conditions and there is usually a large enough system to support the above-ground parts. The clearest examples of yield losses due to poor rooting come from studies on soil compaction and from the poor control of root diseases such as Take-all and pests such as cereal cyst nematode. Even in these cases, however, the effect on yield depends on other factors such as rainfall. The risk of root lodging is increased where the root system is not strong enough. It is not clear whether cereal root systems could be modified to allow the crops to make better use of water and nutrients, particularly nitrogen.

Diagnosis of rooting problems

Some problems will occur equally throughout a field and are thus not obvious. Others may occur in patches characterised by a lower or yellower crop cover, shorter crops or premature ripening. Rooting problems are best seen by digging soil pits down to a depth of between 0.5 to 1.2 m (depending on soil type) and examining them for signs of harder layers of soil and areas of poor rooting. Pits are normally dug after harvest when the soil is moist but this will miss any temporary problems that occurred earlier in the growing season.

Farming operations that affect rooting

Farmers can modify the root system either deliberately or as a consequence of other actions. The operations that influence rooting include: rotation, variety choice, cultivations, seed rate, sowing date, nitrogen rate and timing and plant growth regulator application. However, for some of these farmers have no real choice and others take place too late to have a significant effect. On heavier soils a key decision is whether or not to carry out expensive cultivations such as sub-soiling and better guidance is needed. Problems are likely to be greatest for spring crops when roots compete strongly with the shoots for the products of photosynthesis, particularly in dry springs.

Varietal differences in rooting

Varieties differ in rooting pattern in the same way as there are differences in straw length and canopy characteristics. Differences in nitrogen scavenging ability have been noted and there are differences in the response to pH. However, there is insufficient knowledge to identify good characters for use in a plant breeding programme.