FIELD AMELIORATION OF ACIDIC SOILS IN SOUTH-EAST QUEENSLAND - II - EFFECT OF AMENDMENTS ON THE YIELD AND LEAF NUTRIENT COMPOSITION OF MAIZE

The yield of maize, grown on acidic soils with various rates of lime, was measured in replicated field trials at each of 19 sites ih south-e ast Queensland. Treatments comprising single rates of gypsum, phosphog ypsum, and calcium silicate las Portland cement) were incorporated int o the trial design at selected sites. At 12 of the sites, lime signifi cantly (P < 0.05) increased grain yield. Because Ca was applied as a b asal nutrient the lime responses were attributed mainly to the amelior ation of Al and/or Mn toxicities and this was supported by the observa tion that 90% maximum yield was attained at pH(w) values of around 5.0 -5.5. Soil pH(w) values of around 5.5 would appear to be adequate for optimal maize growth in the region and there was little evidence to su pport liming to higher pH values. High lime rates resulted in signific ant (P < 0.05) grain yield reduction relative to the maximum yield at 3 sites with concomitant soil pH(w) values of 6.7, 7.1, and 7.2, but l eaf analysis did not provide a conclusive explanation for the yield re ductions. Lime significantly (P < 0.05) increased leaf tissue P concen trations at 6 sites, whereas Zn and Mn concentrations were decreased a t 7 and 10 sites, respectively. Across all sites, there were no consis tent trends with respect to the effect of lime on N, K, S, and Mg conc entrations. Although gypsum and/or phosphogypsum increased grain yield at 3 sites, there was little evidence that amendments other than lime or dolomite type products would have widespread potential for amelior ating soils where Al and/or Mn toxicities are limiting crop growth in the region.