New ideas mean lodging neednt

21 March 1997

New ideas mean lodging neednt

be a downer

New ideas for assessing lodging risk are well received in the latest of our series bringing HGCA-funded researchers and growers face to face. Andrew Blake reports

FLAT cereals cost UK growers a lot – £94m in 1992 alone, estimates ADASs John Spink, joint researcher with Jonathan Griffin of Monsanto on a £350,000 HGCA project.

Growth regulators help avoid some of the damage, but they also cost money, and late treatments can be risky.

By understanding more about what makes crops go down it should be possible to predict more precisely which will do so and tailor husbandry accordingly, says Mr Spink.

"Lodging has as much if not more to do with the crop as the weather," he stresses. Proof that downed corn is not solely due to an act of God in July comes from ADAS Rosemaund. Since 1980 there has been little link between rain that month and the amount of lodging.

"In 1996 we had a fair bit of lodging though it was relatively dry. In 1988 it was a very wet July but we got practically no lodging."

The four-and-a-half year project, due for report in June, examined several features of the crop, both above and below ground, and the soil. The aim is a practical scoring system based on in-season grower measurements which when combined will give a more accurate guide to the need for growth regulators.

A key finding is that what goes on below ground matters as much as what happens above in determining whether a crop lodges.

Taller heavier canopied plants, such as those encouraged by early drilling, are naturally more vulnerable to lodging, says Mr Griffin. This is because they exert more leverage on the lower parts when the wind blows.

Resisting this aerial force are two below ground forces, one resulting from stem base strength, the other from the cone of anchoring crown roots, he explains. Crown roots are thickened and lignified and usually confined to the top 25-50mm (1-2in) of soil.

Stem base strength is varietal, but the fact that some short varieties have unexpectedly poor NIAB standing power ratings may be due to poor crown rooting, says Mr Spink. "There is scope for more work to be done on this."

A strong influence on cone size is seed rate. Dense crops from high rates have much less root anchorage because plant competition restricts cone diameter. So spring plant populations will be vital inputs in lodging risk calculations, he says.

Soil – its type, water content and crumb structure – is the other main area of project exploration.

Much depends on clay content. Clays are inherently stronger than sands and so tend to hold crops more firmly. But as soils become wet they lose their strength. "As the soil goes from bone dry to field capacity that strength decreases massively. On a high clay soil it goes down about twelvefold."

Sand strength drops about fivefold, albeit to a similar level. But the significant point is that it does so with much less rain because clay has a higher water holding capacity, explains Mr Spink.

Soils with good crumb structure are much weaker than those that are capped, he adds.

"If you look at the crop and you know it is poorly anchored you might be better off trying to consolidate the soil than applying a PGR."

Any wetter and its bound to go down! Richard Butler (blue jacket) and agronomist Roger Organ (right) are intrigued by the lodging work carried out by John Spink (left) andf Jonathan Griffin.

Below: Better than a boot? Soil strength can be measured accurately with this gadget – the equivalent of a torque wrench. A typical reading for a sandy loam is 25 kilopascals. A clay soil of similiar moisture content registers 40kp.

Wheat plants from the same field have very different root anchorage according to soil type. The one on the right came from greensand, the other from silty clay loam.

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