Correction of manganese deficiency in barley crops on calcareous soils. 2. Comparison of mixed and compound fertilizers

Mixed and compound fertilizers made from superphosphate and manganous sulphate were compared in field experiments as sources of manganese for barley on the calcareous soils of southern Yorke Peninsula, South Australia. The compound fertilizers were made by blending manganous sulphate with 'den-fresh' superphosphate before the granulation process: mixed fertilizers were made by mixing the components after manufacture. The fertilizers were applied at sowing at rates of 19 kg haw1P and 16 kg haelMn in one experiment and 28 kg ha-1 P and 6 kg ha-1 Mn in a second experiment. In the latter, up to three foliar sprays of manganous sulphate (1.3 kg ha-1 Mn per spray) were applied in addition. The rate at which the fertilizers reacted with the soil was studied in an incubation experiment, and the nutrient content of particle-size fractions of the fertilizers was also determined. Plant dry weight, manganese and phosphorus uptake, and grain yield were increased to a greater extent by application of the compound fertilizer than by the mixed fertilizer. Application of compound fertilizers at sowing also delayed the appearance of manganese deficiency symptoms in crops by two weeks compared with mixed fertilizers. Neither fertilizer prevented the occurrence of manganese deficiency and further yield increases were obtained by subsequent foliar sprays of manganous sulphate. Fertilizer manganese was rapidly immobilized in the soil. After 167 hours' incubation, approximately three quarters of that added in manganous sulphate, and in the mixed and compound fertilizers was not extractable in divalent form. The variation in nutrient content of particle size fractions of a compound fertilizer was much less than that in a mixed fertilizer.