Reaction of zinc with soil affecting its availability to subterranean clover. 1. The relationship between critical concentrations of extractable zinc and properties of Australian soils responsive to applied zinc

Abstract

A number of glasshouse experiments were conducted in which subterranean clover cv. Nungarin was grown in pots of a wide range of Australian soils to which zinc was added. Levels of zinc extractable in DTPA and in ammonium oxalate were determined and related to the growth of clover. DPTA extractable zinc (ZnD) was found to be a reliable predictor of the response of subclover to zinc added to the soils. The critical levels of ZnD, determined for the maximum growth of subterranean clover were found to vary markedly among the soil types. No simple linear relationship between the critical ZnD levels and any one soil property were found. The ZnD critical levels were found to be related to the clay content (%) and pH (1 : 5 water). The selected model in a stepwise linear regression was: Y (DTPA critical level) = -0.087 + 0.039 pH, + 0.005 clay (%). For the non-responsive soils, ZnD was found to be above the calculated critical ZnD level.