Recommended post-harvest fertiliser products

When hay or silage is harvested, large amounts of nutrients are removed. Nitrogen (N) is removed in the greatest amounts, followed by potassium (K) and phosphorus (P) as shown in Table 1. Hay removes less K than silage as it is harvested at a more mature stage when herbage K levels are lower.

Potassium has the second-highest removal rate behind N, and is especially important for post-harvest clovers which take time to recover from being shaded by grasses. If any nutrient is in short supply, clovers suffer first as their root system is shallower than ryegrasses. Lack of K can limit clover growth, which in turn affects long-term pasture production, quality and N supply.

Soil testing annually provides an accurate picture of soil fertility and nutrient requirements. Herbage analysis is also useful when multiple cuts are taken from a crop.

Apply N strategically during the crop’s growing season. Applying it when the paddock is first shut up aids dry matter response and gets the paddock back in the grazing rotation faster. If more than one cut is taken, applying N with maintenance fertiliser after each cut aids recovery and improves the yield of the next cut.

If Quick K test is under 5, apply K before the paddock is shut up, otherwise apply it post-harvest. Post-harvest K applications can be split if large amounts are required to achieve the desired soil test range, or if winter leaching is a risk.

Avoid overapplying K, as growing plants take up excess K without converting it into extra growth. This could reduce the return on fertiliser investment if elevated K herbage levels in conserved feed and/or re-growing pasture are removed as hay or silage.

If Olsen P levels are optimal: 20 to 30 for ash and sedimentary soils or 35 to 45 for pumice and peat soils, maintenance P can be applied at any time. If Olsen P is below optimal, apply P when the paddock is shut up.

Table 1: Average nutrient removal rates (kg per tonne of dry matter)

Ensure sufficient sulphur (S) is applied annually, and magnesium (Mg) may also be needed if soil test levels are below optimal (8 to 10). The fertiliser products below in Table 2 are recommended to be applied post-harvest and takes care of the nutrients removed by the harvest. Note, regular maintenance fertiliser may still be needed.

The new sustainability-focused PastureSure fertiliser range includes 5K, 10K and 15K options which provide varying amounts of N, P and K, as well as S and Mg.

For assistance with planning a fertiliser plan for your farm, contact your local PGG Wrightson Technical Field Representative.