25 February 2000

Underground route to better crop performance

In our latest article looking

at the prospects for arable

farming we examine scope

for improving management of

out-of-sight root growth.

Andrew Blake reports

COMPARED with our knowledge of crop canopies, todays understanding of what occurs beneath the soil is sketchy, says Ian Bingham, SAC crop scientist and one of the HGCAs new trio of research overseers.

"But by understanding how root systems function and control the canopy, it should be possible to develop new varieties and husbandry tools to meet the challenges of the future," says Dr Bingham. "Root and soil management is a key area for new HGCA research."

Most agriculturists can define a good seed-bed for a given crop, he says. "But that is just the start. What we need to do is ensure that the size and distribution of roots is sufficient to sustain the canopy later on during, say, cereal grain formation and filling."

One of the aims is to match root systems more effectively to particular soil conditions. The alternative route of remedying soil problems or applying other corrective measures, such as irrigation, can be expensive, he explains.

In the short term, perhaps five years, this could partly be achieved through better choice of varieties and sowing dates. "We need management guidelines for the more difficult soils.

"We also need better guidelines on cultivations and subsoiling. There is a lot of renewed interest in minimal cultivations and we need to be able to offer more specific advice on where and when it will work and where it wont. There is still a great deal of uncertainty over the need for subsoiling.

Understanding the role of roots in crop growth is also essential. Scientists are increasingly aware of the role of plant hormones like cytokinins and abscissic acid in allowing plants to respond to their surroundings, says Dr Bingham.

Roots and crop canopies are inevitably linked. But an ability to manipulate the hormonal messages roots send to aerial parts of plants is potentially exciting, he suggests.

"We already know of mutants where the signals between roots and shoots are weaker than in other plants of the same species. That raises the possibility of exploiting that difference."

Scottish-funded basic research at SAC and elsewhere on the way roots react to different soil properties offers the foundation for applied work that could have more practical spin-offs, he believes.

"Roots are unlikely to limit yield on deep, fertile, well structured soil with plenty of moisture. What we must do is focus our attention on the more difficult soils to find ways of creating root systems that can cope in these conditions."

Much research has been carried out on mycorrhizal fungi and other organisms which interact with roots and the soil and which can help ward off plant pathogens. "But we have only recently developed molecular techniques to distinguish between the different types," says Dr Bingham.

"In 10-15 years we might be able to develop those with specific beneficial effects. They could be particularly useful for helping reduce nutrient inputs and the effects of root diseases on crops."

Some genes involved in extracting nutrient ions from the soil and in root branching have already been pinpointed. "Now we need to see whether any benefits can be obtained from them and whether those could be transferred to the field."

A pressing requirement to advance much of the work is a quicker method of measuring roots, stresses Dr Bingham. "Traditionally it is a very time-consuming process."

A faster tool could allow speedy assessment of any useful differences between the rooting systems of varieties in NIAB trials.

The SAC hopes to start work soon developing an air-knife used by civil engineers to remove soil from around pipelines. Driven by compressed air the tool could be modified to blast soil away from crop roots so that they can be photographed and analysed by computer.

Some damage of the finer roots would be inevitable. "But a semi-quantitative image may be good enough for our needs. It is only a research idea at the moment. But it could produce sets of root distribution pictures. These could then be related to crop canopy characteristics to help growers identify when rooting may be limiting to yield." &#42


&#8226 In relative infancy.

&#8226 Key HGCA thrust.

&#8226 Practical guidleines aim.

&#8226 Speedy measuring need.

Crop growth beneath the surface is just as important as that above ground. But we know relatively little about how it drives output, says SAC crop scientist Ian Bingham (inset).