3Phase fertiliser program for broccoli on sandy soils

Three growth phases

Phase 1: crop establishment

Good growth in the first two to four weeks of crop life is critical for achieving high marketable yields. Maximising growth rates in this phase not only has a major impact on final yield but also on the number of days from planting to harvest. These benefits cannot be made up in later growth phases if early growth is inadequate.

To maximise crop nutrition and growth in the establishment phase, keep fertilisers for as long as possible in the top 10–15cm of soil where young roots are growing.

During crop establishment, twice-weekly applications of fertiliser containing low rates of nitrogen and potassium, by spraying or broadcasting, are required.

Both methods place enough fertiliser within the reach of roots to maintain a steady nutrient supply without excessive loss to the environment (Figure 2) as long as irrigation practices are good and rainfall is not excessive.

Figure 2 Broadcast or spray applications of fertiliser during crop establishment place nutrients where young roots have access

Applying granular NPK fertiliser to the soil surface on the day of planting is critically important for achieving maximum yields, whether spraying or broadcasting is used for following applications.

Phase 2: rapid growth

Once the root system is established, fertiliser is most effectively applied weekly by banded application (Figure 3) until row closure.

Figure 3 Banded fertiliser application in the space between pairs of rows is an efficient way to achieve root uptake during the rapid growth phase

Fertigation or broadcasting can also be used in this phase. It is difficult to apply the required rates of fertiliser with these methods without unnecessary water use or the risk of damage from undissolved fertiliser granules lodging on heads or in foliage.

Banding with compound granular fertiliser is most suitable as it minimises labour costs compared to single nutrient fertilisers by applying the required rate of nitrogen, phosphorus and potassium in one pass.

Phase 3: maturation

After row closure, the head and frame fill out, drawing accumulated nutrients from the frame developed in earlier stages as well as from the soil. Continued application of nitrogen and potassium is required in the three to five weeks between row closure and harvest.

Weekly fertigation with nitrogen and potassium is required until the week of harvest.

This method of application can involve some unavoidable losses from overspray on adjacent crops, younger plantings or uncropped ground, but other methods used in earlier phases are less safe for the crop or practical in this phase.