28 May 1999

IGERtrials show S yield benefits on sandy loams

APPLYING sulphur to sandy loam soil increases grass yield by up to 10t/ha (4t/acre) and improves nitrogen use efficiency.

But less benefit is found on clay loam soils, according to studies over the past two years.

That was the finding Lorna Brown, an Institute of Grassland and Environmental Research soil scientist, reported at Grassland 99. Kemira-funded studies compared fertiliser treatments with and without sulphur on two Devon sites over two years, one with sandy loam and one with clay loam soil.

Plots were treated with either high or low nitrogen, 450kg N/ha (360 units/acre) or 200kg N/ha (160 units/acre), and either 45.6kg of sulphur/ha (36.5 units/acre) or no sulphur. The sulphur was split into three dressings.

When sulphur fertiliser was used on sandy loam soils, with the higher rate of nitrogen, a 16% and 30% increase in herbage yields was recorded in 1997 and 1998, respectively, said Dr Brown.

But the timing extra growth occurred varied in the different growing seasons: In 1997, first cut yield was 25% higher when the crop was sulphur treated, she said.

On sandy loam soil there is less nitrogen lost through leaching and as gas into the atmosphere through denitrification when using sulphur fertiliser. Of the two years, nitrogen leaching decreased most in 1998 at 72% less than plots without sulphur, in 1997 it was 58% lower. Peak nitrogen concentration in soil also stayed below the EC limit when sulphur was applied, whereas it increased above the EC limit without sulphur fertiliser, she added.

"These results mean that on sandy loam soils you can reduce nitrogen losses without a yield penalty and increase herbage yields using sulphur," said Dr Brown.

But on the clay loam soil site there was only a small increase in herbage yield and there was no saving in nitrogen losses. "On heavy soils less sulphur is leached and there is a better supply of sulphur through mineralisation, so the response is much lower."

Kemiras George Fisher added that sulphur could be used to hold yields and reduce nitrogen applications, saving 30kg/ha of nitrogen (24 units/acre). This would allow producers to comply with regulations in Nitrate Vulnerable Zones.

But to find out whether more sulphur is needed, producers should do a tissue test to identify the nitrogen:sulphur ratio.

Kemiras Roger Chesher added that using a fertiliser containing sulphur could be worth £200/ha (£80/acre) – based on producing an extra 10t of fresh grass/ha (4t/acre) worth £20/t – without spending more on fertiliser.