The effect of granule size of compound fertilizers on barley crops grown in calcareous soils

The effect of variations in the granule size of compound fertilizers on dry matter, grain yield and nutrient uptake of barley was evaluated in three field experiments on the calcareous soil (> 80 per cent CaCO3) of southern Yorke Peninsula, South Australia. This soil has a high capacity to fix applied phosphorus and manganese. The fertilizers contained superphosphate, manganous and cupric sulphates, and, in two experiments, elemental sulphur as well. The fertilizers were banded with the seed. In all experiments, small fertilizer granules with diameters less than 2.1 mm produced greater grain 5elds than the larger granules. In two of the three experiments, a commercial-sized fertilizer (< 4.8 mm diam.) produced yields similar to those of the small granules. In two of the experiments, plant dry weight, phosphorus and manganese uptake was also significantly increased with decreasing granule size, particularly during rapid plant growth from mid-tillering to late stem extension. This response was more pronounced where the phosphate application rate was suboptimal. In the third experiment, conducted in a year of above average rainfall, the responses were variable and usually not significant. From measurements of granule distribution we suggest that the greater plant response to small granules is due to the better distribution of fertilizer within the soil. This appears to increase contact between plant roots and fertilizer and hence increases the nutrient uptake by the crop.