Pea crops also found wanting

22 January 2000

Pea crops also found wanting

ITS not just potatoes and oilseed rape that may benefit from a sulphur fertiliser boost in the wake of industrial decline and cleaner air. Pea crops could also be suffering the effects of a sulphur shortage.

The first indication of a potential problem comes from new research by Dr Fangjie Zhao of IACR-Rothamsted, funded by the Processors and Growers Research Organisation (PGRO). At an acutely S-deficient site in Woburn, Bedfordshire, sulphur soil treatments have boosted pea yields by up to 20%, and pea seed numbers by slightly more.

For growers, possible yield losses are serious. But even more important to feed compounders might be the effect on quality. Sulphur deficiency could pull down the nutritional value of feed pulses by limiting the amount of methionine, an important amino acid.

Dr Zhaos research is still in the preliminary stages, but it appears that pulses may have a similar S requirement to that of wheat, at about 15kgS/ha. Brassicas such as rape have the highest demand, approximately five times greater.

Symptoms of sulphur deficiency show up as a dramatic yellowing of all leaves on the plant at once, not just younger tissue. The effect is marked because peas need sulphur at an early stage, in order to feed the nitrogen fixation process, which occurs within the root nodules. As soon as sulphur runs low, then the whole plant is rapidly starved of nitrogen.

Treatment with Thiovit, applied as a soil drench prior to emergence, has shown yield improvements of up to 5.7t/ha (2.3t/acre). "Thiovit has given us the best results, but theres a possibility that it could also have had a fungicidal effect on powdery mildew which may have boosted yield," says Dr Zhao.

He is seeking a reliable system of S deficiency diagnosis, using tissue testing. Treatment boosts the number of pods per plant, occasionally doubling pod numbers; a similar effect is seen with oilseed rape.

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