Could sewage sludge be limiting take-all losses?
Could sewage sludge be limiting take-all losses?
By Hans Luers
APPLYING digested sewage sludge prior to a second wheat crop can lift yields and gross margins to the level of a first wheat by suppressing the effects of take-all, believes Peter Taylor, an independent crop consultant operating in Essex and Herts.
He decided to investigate after clients reported second wheats treated with Terra digested sewage sludge yielding on a par with, and sometimes above, first wheats.
That was despite mineral fertiliser rates having been slashed, in the case of nitrogen by anything up to 50kg/ha. Yield benefits were even observed where the organic manure was applied earlier in the rotation.
The chance discovery came in the wake of the increased use of Thames Waters sewage-based Terra Cake as growers looked for cheaper sources of P and K, says Mr Taylor.
"On our heavier soils there are limited slots for applying sewage sludge in the rotation, such as oilseed rape, hence our interest in applying it for second wheats. We were expecting to see a financial advantage from lower mineral fertiliser rates, but the yield benefits have been far greater than we imagined."
In 1999 sludge-treated second wheat on one Herts clients farm yielded on a par with first wheats. The following year sludge-treated second wheat Rialto yielded 5% better than the same variety grown as a first wheat on an identical soil type. Both results were despite second wheats receiving no mineral P and K and 40-50kg/ha less nitrogen.
Similar results have been recorded on other clay soil farms in Herts and Essex.
Mr Taylor believes the use of organic sewage sludge counteracts the effects of take-all, although there is no scientific proof. The most likely cause is the balanced and continuous nutrient supply to the growing crop, in particular the availability of phosphate and nitrogen, he suggests. Soil conditioning may also have an effect, particularly where the product is applied over a number of years.
"Take-all affects root development and I can only assume that the combination of ample phosphate and regular nitrogen from the extra mineralisation provides the plants with the right amount of nutrients, from establishment right through to grain filling, and this somehow stimulates root growth to the extent that it actually ameliorates the effects of take-all and possibly other root diseases," says Mr Taylor. *
Could sewage sludge be providing slow release nutrients to compensate for the root-ravaging effects of take-all, asks independent consultant Peter Taylor.