Development and prediction of sulphur deficiency in winter oilseed rape

Abstract

Amounts of sulphur (S) deposited from the atmosphere and of extractable S in the soil at 30, 60 and 90 cm depths were monitored at periodic intervals through the growing season in 16 field experiments evaluating crop response to spring-applied S fertiliser (40 or 50 kg S/ha) during the 1991-92 and 1992-93 seasons. Large significant (P < 0.1) increases in seed yield, ranging from 15% to 74%, were obtained at S sites located on sandy soils or shallow soils over chalk in Scotland, northern, south-west and eastern England. Transient symptoms of S deficiency were observed at a further 4 sites in these areas but there was no yield response. Seed glucosinolate concentrations were increased 2-3 fold by application of S at S-deficient sites, although this was not consistent. Total amounts of S deposited from the atmosphere in 1993 ranged from 9.3 to 17.6 kg/ha and were lowest in Scotland. There was wide variation between sites in the amounts of S in the soil profile to 90 cm but no difference in amounts of S at any depth between autumn and spring. Crop uptake of S was significantly increased by addition of fertiliser S at most sites but did not exceed 55 kg/ha.

Yield responsive sites were distinguished by a low (< 4 mg/g)concentration of S in young fully expanded leaves at flowering. There was a significant relationship between leaf S content at this growth stage and the concentration in the soil, either to 30 cm or averaged over the soil profile, of extractable sulphate-S as measured by ion chromatography (IC) and extractable total S as measured by inductively coupled plasma atomic emission spectrometry (ICP-AES). Inorganic S04-S measured by IC was, on average, 50%, 60% and 70% of soil S measured by ICP-AES at 30, 60 and 90 cm, respectively. Yield responsive sites were generally but not exclusively associated with extractable S04-S and S concentrations in the soil of < 4 and < 8 mg/kg, respectively. It was concluded that soil analysis in autumn or spring was a useful but less reliable guide to S deficiency in winter oilseed rape than leaf analysis.