Influence of sulfur and phosphorus placement, and sulfur particle size, on elemental sulfur oxidation and the growth response of maize (Zea mays)

Abstract

The oxidation rate of elemental sulfur (S) can be manipulated by a number of controllable factors to match formation of sulfate to plant demand. Two of these factors are particle size and the presence of adequate nutrients for the oxidising bacteria. A factorial experiment was conducted in a glasshouse consisting of 3 combinations of S and phosphorus (P) placements × 2 S particle sizes [ ³⁵S-labelled 50–150 µm (fine sulfur, S_f) and 150–250 µm (coarse sulfur, S_c)] × 2 harvesting times of maize (Zea mays) (28 and 56 days). In the 3 fertiliser placement treatments, all of the S was evenly mixed with the soil in the front compartment of a split-root box. The treatments differed in the placement of the P fertiliser: (i) all of the P was applied in the front compartment with the S (SP_F); (ii) the P was applied evenly throughout the soil in both compartments (SP_FB); and (iii) all of the P was applied in the back compartment (SP_B). A high P- and S-sorbing basaltic soil (Haplohumult) from Walcha, New South Wales, was used in the split-root boxes.

Plant dry weight and fertiliser S uptake were increased when P was mixed with elemental S. Elemental S oxidation after 28 days was higher when mixed with P than when separated from P, and higher with S_f than with S_c. Root proliferation occurred in direct response to the placement of P. There were significant linear relationships between the amount of applied P in the front compartment and root length and root surface area of the front compartment roots.

This study shows that the increase in S uptake by the plant from elemental S when it was mixed with P was due to the combined effect of P on elemental S oxidation and on root proliferation.