Recyclet

Ammonium nitrate prices are rising particularly steeply, as suppliers struggle to meet increasing demand, he says. But, in the short- to medium-term, there is more capacity coming on stream to produce urea, so it is marginally cheaper and may be something worth considering. "Urea is substantially cheaper that AN as spot price for the products is the same, and given 46% N compared to 34.5%N there is a real difference."

Urea differs from AN though, so growers have to understand how to use it, says Mr Norman. Principally it is less readily available than AN, so needs to be applied earlier. "In cold conditions it might take 10 days or so for it to be available to the crop and in warmer weather nearer 5-7 days. This is completely different to AN, which is available almost immediately."

Urea is also more prone to volatilisation losses, particularly when soils are warm and dry, he adds. DEFRA field experiments suggest losses from granular urea can be as high as 22% of total N applied, compared with 14% for liquid urea and just 2% from AN. "There's a massive range though, depending on soil and weather conditions."

Optimum rates do not change

Mr Norman advises against cutting back on nitrogen applications, even if fertiliser is more expensive. Results from four years of Velcourt/ Yara nitrogen dose rate response work found that the physical and economic optimum remained around 220kg N/ha, whatever the variety, grain or nitrogen price.

"The objective is still to produce as much yield as possible. Crop uptake doesn't change so the optimum stays the same. But profitability will be reduced, so you may have to find other ways of mitigating high nitrogen prices, such as using compost, biosolids, or manures."

It is also important to ensure other nutrients are up to the optimum level and the soil pH is right to maximise crop uptake and nitrogen utilisation, he adds.

"Ideally every farm should be fully pH-tested every four years, so a quarter of the farm should be done each year," says Digby Burley of R&T Liming. "pH is crucial for the rooting and nutrient uptake of every crop, not just rape or sugar beet."

Recycled plasterboard may have soil benefits

Gypsum from recycled plasterboard could be a useful alternative to conventional powdered gypsum, trials funded by Waste & Resources Action Programme (WRAP) on one Velcourt farm in Suffolk suggest. "It's as good, if not slightly better," trials officer, Paul Cartwright says.

It has been found to be a useful soil improver, particularly on heavy clay, low organic matter, or saline coastal soils and there have been signs of benefits for potato crops in improved skin finish and less growth cracking, he says. "It doesn't have any liming value though."

Although some recycling companies, such as Recyclet Ltd in Brigg, are interested in developing the agricultural uses, availability of the product can be very limited, he says. Applying recycled gypsum to land is also subject to waste management regulations, so the cost of registering an exemption (approximately £11/ha) and the associated time and paperwork can put growers off, he says. "We've got some farms using it already, but the price has to be competitive with supplies of mineral gypsum."

Mr Cartwright hopes that a new specification for recycled gypsum, similar to the BSI PAS100 compost standard, should reduce the cost and make it more accessible for growers. "We're working with WRAP and the Environment Agency to develop a quality protocol at the moment."