Management of sulphur fertiliser to improve durum wheat production and minimise S leaching

Optimisation of S release from decomposing soil organic matter and S fertiliser related to plant S uptake is a central issue and goal in applied research in agricultural systems. Two lysimeter experiments were conducted in central Italy in two subsequent seasons on two commercial durum wheat cultivars to investigate the effects on yield, S and N uptake and leaching of different rates of N and S fertilisers, soil type and split applications of S. Sulphur fertiliser increased grain yield and N and S uptake of both varieties. Grain yield increase was mainly due to an increase of the number of kernels per spike, which was interpreted as a stimulation of the initiation of spikelets and/or florets, or to a reduction the floret mortality. As an average of the two seasons, S leaching during wheat cycle was 35 kg S ha−1. Sulphur fertiliser rate increased S concentration in drainage water and consequently S leached during wheat cycle. Compared to unfertilised control, S leached was by 13 kg ha−1 higher at 60 kg S ha−1 and by 19 kg ha−1 higher at 120 kg S ha−1. The splitting of sulphur fertiliser during crop cycle modified both grain yield and S leaching. The highest grain yield and S plant uptake was obtained with the splitting of S rate into 60 kg S ha−1 before seeding and 60 kg S ha−1 at stem elongation and the lowest amount of S lost by leaching occurred with the application of 36 kg S ha−1 before seeding and 84 kg S ha−1 at stem elongation. Sulphur output was equally accounted for by leaching and plant uptake. The input–output balance of S was positive in both experiments only when the higher S rate was applied, as more S was imported than removed. Thus, no substantial S deficit may be expected in short term, provided that high S fertiliser rate is applied and the availability of S is synchronised with plant needs.