26 May 1995

Higher yields and less waste

APPLYING nitrogen according to measured crop need, rather than expected demand, can give higher yields with less wasted fertiliser.

Such targeted applications can outstrip current recommendations, argues Dr Donald MacKerron of SCRI, Dundee. "They may be right on average. But is that just a polite way of saying theyre wrong all the time."

He advocates a system based on applying three-quarters of the crops need in the usual way, in line with recommendations. But this is then supplemented according to measured crop need.

That is judged by testing the nitrogen content of the whole plant – leaves, stems and tubers – two or three times early in the season. "Sadly we cant recommend petiole sap analysis. It doesnt work. But plotting the entire plants nitrogen content against fresh weight does give a good guide."

The supplement is provided by 12kg/ha (10 units an acre) applications of liquid urea and ammonium sulphate, tank mixed with blight sprays. &#42