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The residual effects of fertilizer zinc on a black earth soil from North Western New South Wales

R.G. Weir1 and J. Holland2

1 Biological and Chemical Research Institute, Department of Agriculture, Ryalmere, N.S.W. 3116
Agricultural Research Centre. Department of Agriculture, Tamworth, N.S.W. 3340

Zinc deficiency affects several crops including maize when grown on the extensive black earth soils of north western New South Wales. Application of zinc to the soil corrects the deficiency symptoms and increases yield. Producers need to have information on the effects of rates of initial and subsequent applications on yields and the residual effects to assist them in planning fertilizer programs for these soils.

In the 1973/73 season, a trial was established on the Liverpool Plains Research Station at Breeza, to study rates, methods of application and residual effects of zinc oxide on hybrid maize XL45. Zinc was either broadcast or drilled at initial rates of 0, 5.6, 11.3 or 38 kg Zn ha-l and 0 or 5.6 kg Zn ha-l in subsequent seasons.

In most seasons treatment with zinc almost doubled grain yields. Broadcasting and working in was more effective than drilling zinc with the fertilizer. Table 1 summarises for the broadcast treatments the effects of initial rate and annual applications of zinc on maize yields for each season.

TABLE l. Yield of maize grain (kg ha-l)

There were large yield responses to the initial 5.6 kg of Zn with small increases up to the highest rate of 28 kg Zn ha-l. The shape of the yield curve has remained basically the same during the six years of the trial. Broadcasting and working in the initial zinc treatments gave much higher yields than drilling in the first two years.

Residual effects of the initial 5.6, 11.2 and 38 kg Zn remained evident throughout the six years and the higher rates continued to produce highest yields.

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