The Relationship Between The Pre Plant Nitrate N And Relative Yield Of Wheat

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gure 1 shows the relationship between the pre-plant nitrate-N and relative yield of wheat. At the Australian level, the CV90 of 47kg N/ha has a narrow CR90 of 43-51kg nitrate-N/ha. However when the data is presented in terms of states, Queensland, Victoria and South Australia, differences between CV90 and CR90 are evident. The lowest CV90 is Queensland with 43kg nitrate-N/ha, followed by South Australia with 55kg nitrate-N/ha and the highest value is for Victoria at 62kg nitrate-N/ha. Corresponding to the CV90 values are the CR90 values with Queensland 39-48kg nitrate-N/ha, SA 50-61kg nitrate-N/ha and Victoria 47-82kg nitrate-N/ha. Whilst Queensland and South Australia have similarly narrow CR90 values, Victoria’s CR90 is wider. This indicates many high-yielding trials producing Ymax in excess of 4 or 5t/ha and a similar number of low-yielding trials, averaging 5t/ha. The r value for each relationship was as follows: 1-2t/ha, 0.36; 2-3t/ha, 0.45; 3-4t/ha, 0.38; 4-5t/ha, 0.69 and >5t/ha, 0.63.

From Figure 3, increasing in-crop rainfall has resulted in a trend of small increases in soil nitrate-N kg/ha demand for Queensland and South Australian data. Against the trend is the Queensland >250mm value which showed a decline in value to 36 nitrate-N kg/ha from the previous 200-250mm demand for 44 nitrate-N kg/ha. In contrast, the South Australian wheat data has continued to use higher soil nitrate-N values, of 53 nitrate-N kg/ha at 350mm, without any decline at

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