Plant leaves and stems are not only powerhouses that produce energy for growth but together with roots are also storage organs. In good conditions, they can accumulate excess nutrients and remobilise them to maintain optimum growth when nutrient availability is low. This ‘natural buffering’ effect should not be underestimated and can help simplify fertiliser management.
Not all fertilisers need to be applied all the time. The natural buffering effect cannot be relied upon to sustain the crop when it is young because it does not have a large storage capability. Later, it can reduce the need to side dress nutrients like potassium and phosphorus.
Nitrogen does not accumulate much in plants and the plant buffering effect cannot be relied upon to sustain the crop for long at any growth stage. It does allow weekly applications to be effective on poor soils.
Effect of irrigation
Your fertiliser program is only as good as your irrigation system and management. Well-designed irrigation systems that give a high degree of uniformity are critical to efficient fertiliser use. Irrigation timing and application rates are critical due to nutrient leaching on sandy soils.
Irrigation on young crops should be for short periods so that only a shallow depth of soil is wetted and nutrients are retained near the surface.
Sprinkler shifts should be small so the area being irrigated at any time does not include too many crops or different planting dates. This is particularly critical when fertigating to ensure the right rate of fertiliser for the growth stage of the crop.
Irrigation should not be the only method of wind and erosion control because this leads to water and nutrient wastage.
Crop and equipment matching
You can improve efficiency of fertiliser use by better matching your machinery and irrigation systems to crop age and type.
One of the most common causes of excess fertiliser use comes from ‘the one size fits all’ principle. It is often easier to leave machinery on the same setting all the time and spread that fertiliser rate over all crop stages.
If equipment cannot easily be reset, set banding and broadcasting equipment at a low application rate and make multiple passes over the crop to account for increasing age and demand.
The same problem occurs when fertigation is used and the sprinkler shift is a large area covering multiple crop maturities or types. After row closure, fertigation is often used when other application methods are no longer possible. The fertiliser rate chosen is usually the one considered right for the most mature crop in the shift. This results in waste on all younger plantings. Smaller shifts, coupled with larger areas of the same maturity, are required for high rate fertigation to be efficient.