Archive Article: 1998/01/17
It was the unpleasant smell of liquid sewage that forced a delegation from the local village to protest at Icknield Farm 20 years ago. Now that the product arrives in dried cake form, there is rarely a comment.
Grower Guy Hildred can detect the odour only when it is warm and damp following application to fields on the 810ha (2,000 acres) mixed farm near Wallingford in Oxford-shire. Generally it is no worse than the farms own cattle manure.
But the herd of 110 dairy cows cannot supply all the manure needed to strengthen the clay and flint soils, so Mr Hildred buys in sewage cake for a large proportion of the arable area. It is applied every three years to fields which support cereals, oilseed rape, sugar beet and pulses.
Each sewage recommendation comes with a full nutrient analysis, which enables Mr Hildred to adjust fertiliser inputs with precision. His supplier, Terra EcoSystems of Heathrow, a subsidiary of Thames Water, gives him an estimate for each field of the amount by which he can cut back on additional nitrogen, phosphate and potassium fertilisers. From that Mr Hildred calculates how much to apply in the coming growing season.
"A printout states the financial value of the major nutrients that each application of Terra cake gives, based on current fertiliser prices. Once I have adjusted them to the prices Im paying, I can work out how much Im saving over and above what I would spend on fertiliser," he explains.
Until this season, it has cost 50p/t to have Terra cake delivered and spread, and the value has been estimated at as much as four times its cost. Consequently most fields which hadnt received manure for several years received up to two applications of Terra cake. The exceptions were fields near a borehole or waterway, since that poses a risk of nitrogen leaching and possible runoff. The cake was spread on to stubble at a rate of about 16ha (40 acres) a day from a heap in the corner of each field.
It is difficult to know whether or not treatments lead to yield increases because there could have been other factors involved. The treated milling wheats had extremely good proteins, which could have been a result of the sewage or the season. But Mr Hildred is sure Terra cake was responsible for keeping his arable crops greener for longer in recent dry springs.
"My wheats were greener for at least 10 days longer than other crops in this area, and were more akin to those grown by a neighbouring pig farmer who regularly uses muck. In fields where boreholes prevented some parts being treated, you could see at harvest where the spreader had been by the colour of the crop. Sugar beet fields in particular were green on the treated side and yellow on the other."
The cake released its nutrients so well in last years warm summer that it caught Mr Hildred out more than once. Nitrogen levels in his harvested sugar beet were dangerously high because he didnt reduce his nitrogen fertiliser applications enough to allow for the 80kg/ha the cake released.
Nitrogen
"I wasnt sure there would be sufficient nitrogen early enough for the March drilled crop following an application of sewage in January, so I cut down by only 40kg/ha. As it was, I think Id have got away with 80kg/ha less, as Terra had suggested," he acknowledges.
Mr Hildred will be cutting back generally from now on, however. A recent price increase doubling the cost of the Terra cake has caused him to question its value. He will be more selective about where he uses it in future.
"There are many disadvantages to using sewage, and I can put up with them while it is priced at 50p/t but not at £1/t. And I have concerns that the risks perceived by consumers will necessitate a review of the legislation on heavy metals in soils. The limits set are arbitrary, and they differ widely from those in other countries."
Mr Hildred believes the main reasons growers dont widely use sewage are that the product doesnt always arrive at a convenient time, the loss of cropped area for stockpiling it is unacceptable, and that it necessitates ploughing. And although its smell is less of an issue than it was 20 years ago, the association will remain in peoples minds.