ARCHIVE: Fertiliser Manual (RB209)

Checklist for Decision Making

Decisions for fertiliser use must be made for each field separately. Where more than one crop is grown in a field, crops must be considered individually.

  1. Confirm the crop to be grown and the intended market. Identify any specific crop quality requirements for this market.
  2. Identify the dominant soil type in the cropped area (see page 86 and Appendix 1).
  3. Carry out soil analysis for pH, P, K and Mg every 3-5 years (see page 35 and Appendix 3). Target values for vegetable rotations are:
    Soil pH 6.5 or 7.0 for brassicae if clubroot is a problem (pH 5.8 on peat soils)
    Soil P Index 3, K Index 2+, Mg Index 2
  4. Identify the SNS Index of the field either by carrying out soil analysis for soil mineral nitrogen (the Measurement Method, page 95) or by the Field Assessment Method based on previous cropping, previous fertiliser and manure use, soil type and winter rainfall (see page 86). SMN analysis is recommended where nitrogen residues are expected to be moderate or high (e.g. following previous manure use, crops receiving high rates of nitrogen fertiliser or for the second crop in one season). Special care is needed when interpreting soil nitrogen analysis data for shallow rooted vegetable crops or where the rooting depth is restricted (Section 3).
  5. Calculate the nutrients that will be available for crop uptake from organic manures and green waste that have been applied since harvest of the previous crop (Section 2). If using the Field Assessment Method, deduct these nutrients from the recommended rates given in the tables. (Crop assurance schemes and protocols may restrict manure application).
  6. Decide on the strategy for phosphate and potash use. This will be either building up, maintaining or running down the soil Index levels (see pages 38-41). Allow for any surplus or deficit of phosphate or potash applied to previous crops in the rotation.
  7. Calculate the amount of phosphate and potash removed in the harvested crop (see pages 38-41 and Appendix 5). This is the amount of these nutrients that must be replaced in order to maintain the soil at the target Index.
  8. Decide if starter fertiliser or banded fertiliser would be appropriate (see ‘Fertiliser Use for Vegetables’, below).
  9. Using the tables, decide on the required rate of each nutrient. Decide on the optimum timings for fertiliser application; then find the best match for these applications using available fertilisers (see page 102).
  10. Check that the fertiliser spreader is in good working order and has been recently calibrated (see page 49).
  11. Keep an accurate record of all fertilisers and organic manures applied.
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