Effect of sulphur fertilization on growth and chemical composition of sorghum (Sorghum Bicolor L.) and on utilization of sorghum silage fed to wethers

Sulphur (S) is an essential element for plant and animal nutrition, but widespread deficiencies of S occur world wide. Current recommendations for nitrogen (N):S ratios are 15 to 18:1 and 10 to 12:1 for plant and animal nutrition, respectively; but recent information suggests these may not predict animal response. Sorghum is an important crop, particularly in drier climatic regions but little is known concerning S-nutrition for sorghum growth or utilization of S-fertilized forages. Sorghum "Pioneer 947" was grown on a Lucy loamy sand (loamy, siliceous, thermic Arenic Kandiudult) in King William County, VA, with and without S fertilization (0 vs. 138 kg S ha⁻¹ as ammonium sulphate) in a randomized block design with four replications. Sulphur fertilization decreased (P < 0.05) soil pH and increased soil S in the 0 to 25 cm (P < 0.08) and 25 to 50 cm (P < 0.05) soil layers. An increase in Mehlich-I extractable soil P, Mn (P < 0.05) and soil N0₃-N (P < 0.06) at surface 25 cm layer occurred with S-fertilization. At harvest, S-fertilization increased (P < 0.05) S and water soluble carbohydrates and decreased (P < 0.05) N:S ratio and P concentration in whole plants. Sorghum leaves were higher (P < 0.05) in N, S, Ca, Mn and Cu in S fertilized compared to non-S fertilized sorghum. Sulphur fertilization decreased (P < 0.05) concentration of hydrocyanic acid (HCN) in the upper three leaves. A greenhouse experiment was conducted with the Lucy soil and 'Pioneer 947' sorghum to further investigate effects of fertilization (0, 70, and 140 kg S ha ⁻¹) as ammonium sulphate in a completely randomized design with five replications. Sulphur application decreased soil pH, and extractable soil K linearly (P < 0.01), and increased extractable soil S linearly (P < 0.01).