An evaluation of sulfur efficiency parameters in soybean and wheat cropping systems in relation to fertiliser sulfur on a Typic Haplustert

Sulfur (S) efficiency parameters were evaluated in soybean-wheat cropping systems in relation to rates of applied S in field experiments on Typic Haplusterts. The parameters evaluated were grain yield per kg fertiliser S applied, S harvest index (SHI), S utilisation from soil (SUS), and fertiliser (SUF) and S efficiency ratios measured as grain yield per kg S uptake by the shoot or grain yield per kg S uptake by the grain. In addition, grain and straw yields, S uptake by both crops, and fertiliser S requirements for optimum production of the 2 crops were also studied. Both soybean and wheat crops responded significantly to S when applied at 0-40 kg/ha on S-deficient soils. The calculated optimum rates of application of fertiliser S to achieve 90% of the maximum yield were 19-38 kg S/ha for soybean and 28-33 kg S/ha for wheat over the 2-year period. The efficiency of crop production as measured by grain or seed yield per kg S applied was greater at lower rates of S application; however, when fertiliser S was applied at a higher rate than 40 kg S/ha, the efficiency declined. Wheat produced more grain yield per kg S applied than soybean. The SHI indicated more efficient translocation of S to soybean seeds than wheat grain. The SUF was greater in wheat, whereas SUS was similar in both soybean and wheat.