Availability of fertiliser sulphate and elemental sulphur to canola in two consecutive crops

Abstract

Aims: We compared elemental sulphur (ES) and sulphate fertilisers in terms of yield and S uptake. Methods: Two consecutive canola crops were grown on 35S-labelled soil amended with ammonium sulphate, ES-bentonite pastilles (90 % ES), or S-fortified ammonium phosphate (NP) fertilisers containing both sulphate-S and ES (5–8 % ES). The shoot yield, S concentration and specific activity of S in the shoot were determined. Results: In the first crop, the yield was significantly lower in the control (without added ES) and ES pastille treatments than in the other treatments. Sulphur uptake was highly correlated with the added sulphate rate. In the second crop, the yield and S uptake was highest for the S-fortified NP fertilizers. The contribution of ES to the S uptake was circa 20 % in the first crop and 43 % in the second crop for the S-fortified NP fertilisers, but was negligible for the ES pastilles. Modelling indicated an oxidation rate of 0.6 − 0.7 % per day for the S-fortified NP fertilisers and 0.03 % per day for the ES pastilles. Conclusions: The contribution of ES pastilles to S uptake was negligible in both crops. In contrast, S-fortified NP fertilisers showed a significant contribution of ES and higher S availability than sulphate-only fertiliser in the second crop.