Diagnosis of Sulphur deficiency in oilseed rape and wheat

Abstract

The reduction in sulphur dioxide emissions in Western Europe over the last decades and changes in fertilizer practices have resulted in a widespread increase in the occurrence of S deficiency in agricultural crops. However, S deficiency is dependent on soil type and prevailing climatic conditions, and does not occur uniformly across the country, hence there is a need for a reliablem practical, field-based diagnostic test to determine where it is likely to occur. In this study we examined the effect of S deficiency in oilseed rape and wheat on several diagnostic indicators, tissue variation, variations within the growth season, practicality and potential ease of implementation of techniques used.

The controlled environment experiments were performed to investigate the distribution patterns of different S pools within the plan and to examine the effects of S deficiency on growth and pool sizes in oilseed rape and wheat, with the specific objective of identifying parameters suitable as diagnostic indicators of the S nutritional status. The results are summarised as follows:

1) In oilseed rape, the concentration of glutathione in the youngest leaves was approximately three times higher than that in the mature leaves. In wheat, before stem extension there was no significant difference between the glutathione concentrations of different leaves. In both crop species, the glutathione concentration decreased with time.

2) In both crop species, the concentrations of sulphate decreased during S deficiency. In oilseed rape, when the external S supply was sufficient, S accumulated as sulphate, in particular in the mature leaves. During S deficiency, the sulphate concentration in the young leaves was almost completely depleted whereas in the mature leaves about 50% of total S was still present as sulphate. This suggested that the oilseed rape plants were inefficient in redistributing sulphate from the mature leaves to the young leaves when the external S supply was low and this may contribute to the high demand of oilseed rape plants for S.

3) Wheat plants were capable of redistributing S from soluble S pools in leaves to the ears at times of S shortage, but only if during the early growth stages enough S had accumulated to make redistribution possible.

4) In both crop species, protein S was maintained as long as possible at the expense of soluble S pools, so the protein S content decreased only slowly during S deficiency.

5) The effect of S deficiency on the total S concentrations was less pronounced than the effect on the sulphate concentrations. As protein S forms a large portion of total S, this was mainly due to the reason mentioned above that protein S was less affected by S deficiency.

6) In oilseed rape, glucosinolates were not a major source of S during S deficiency.