Improving sulphur recommendations for potatoes

The purpose of this project was to specify conditions under which applications of sulphur to the potato crop can be economically justified.

Objectives:

1. To better quantify the risk to potato yield and quality from sulphur deficiency in potato crops
2. To determine an appropriate S application rate in S deficient circumstances
3. To provide these data and an interpretation to AHDB to enable an update to the new versions of the Nutrient Management Guide.
4. To determine the effect of sulphur application on the accumulation of acrylamide and/or its precursors in cooked potato products.

Key findings:

In those experiments where it was measured, applications of S fertilizers increased petiole sulphate concentration showing the S fertiliser was available to the crop. However, in the 17 experiments reported here, application of S fertiliser had no effect on tuber FW yield or tuber dry matter concentration.

There was no indication that omitting sulphur fertilisers was associated with an increase in tuber concentration of glucose, fructose or asparagine and therefore, S applications, are unlikely to reduce the concentration of acrylamide in cooked product. Since there was no response to S fertiliser it was not possible to determine critical levels of soil or petiole sulphate below which S should be applied with any confidence. However, from these results, it is possible that positive responses to S fertiliser may be seen when soil sulphate is less than 15 mg S/l and when petiole sulphur at 50 days after emergence is less than c. 45 mg/l. However, this would need to be confirmed by experimentation.