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Variable rate fertilization

In the last decade the need to fertilize soils rather than fields has been recognized and has led to the concept of variable fertilizer rates. Variable fertilizer rates have been advocated for a number of reasons:maximizing fertilizer use efficiency, reducing field variability, and minimizing fertilizer losses.

IPNI-1991-CAN-SK9

Overview Related Article
30 Aug 2001

Justification

    Soil properties often vary widely within any given field and, as a consequence, so do fertilizer requirements. In the last decade the need to fertilize soils rather than fields has been recognized and has led to the concept of variable fertilizer rates. Variable fertilizer rates have been advocated for a number of reasons:
      1. Maximizing fertilizer use efficiency. With the emphasis on minimizing inputs, it is desirable to use the fertilizer in those areas where it will result in the greatest yield increase.
      2. Reduce field variability. Fields often vary considerably in terms of yield and also in time to maturity. Fertilizers may reduce this variability.
      3. Soil conservation and rebuilding productivity in eroded areas. Higher fertilizer rates in eroded, nonproductive areas may result in more straw production which will reduce future erosion and in the long run may rebuild soil productivity.
      4. Minimize fertilizer losses. Nitrogen fertilizer is subject to losses to the atmosphere by denitrification and losses to the groundwater by leaching. Consequently, large applications of N-fertilizers should not be placed in positions where potential losses, and hence environmental pollution, are high.

    Clearly, the four objectives of using variable fertilizer rates could lead to different practices. For example, nitrogen responses are strongly dependent on soil water supplies, and hence some argue that nitrogen fertilizer applications should be increased in wetter areas of the field. However, this would also increase the possibility of losses by denitrification or by leaching. High rates of nitrogen fertilizer on the knolls would not likely lead to environmental pollution and might increase straw production with benefits in terms of soil quality, but it may be more economical to produce the extra straw in the low-lying, wetter areas and move it to the knolls. Many questions need to be answered before recommendation on variable fertilizer rate practices in Saskatchewan can be given.