Post-harvest is a valuable window for effective fertiliser decision-making on-farm. Once crops such as maize and cereals are removed, it is a good opportunity to investigate soil nutrient status, soil structure, and residue levels. The fertiliser decisions made during this window can positively impact the future by improving the establishment of the next crop or pasture, encouraging stronger early growth, and potentially improving environmental outcomes.
One of the first considerations is nutrient replacement based on actual crop removal. High-yielding maize silage and cereal crops, especially if straw is removed, typically remove large quantities of Potassium (K) and Phosphorus (P). Nutrient removal of an element like Magnesium (Mg) can be an issue, especially on course (sandy) textured soils. Without replacement, these removals deplete soil reserves that later appear as poor early vigor in the following crop or pasture. Something as simple as a post-harvest soil test, especially Olsen P, K, pH, sulphate-S, and Mg provides a critical snapshot for rebuilding fertility.
Post-harvest is also the ideal time to address soil acidity. Soils under intensive rotations gradually acidify from factors such as ammonium fertilisers natural crop growth, nutrient leaching, and crop removal. Applying lime after harvest allows time to counteract the acidifying effects of the cropping program and correct pH to an ideal level. Most arable and maize systems target a pH of 5.8 to 6.2, which maximises nutrient availability and microbial activity. Therefore, adjusting pH helps the subsequent crops receive the full value of applied fertiliser.
When significant residues remain, particularly in high-stover crops like maize, Nitrogen (N) immobilisation is a risk. Strategic applications of N and Sulphur (S), often as urea or ammonium sulphate, accelerates residue breakdown and reduces early N deficiency in the following crop/pasture. This should always be conducted with local regional environmental rules in mind.
Post-harvest fertiliser planning also plays a role in environmental stewardship. Applying nutrients when soil is warm, biologically active, and not waterlogged reduces the risk of leaching and denitrification. Where winter cover crops are used, modest N and S can promote quick establishment to improve ground cover and N capture over winter.
Ultimately, post-harvest fertiliser decision-making is about replenishing soil nutrient reserves, correcting pH, managing potential crop residue issues, and supporting soil biology. Together, they contribute to a stronger, more resilient crop or pasture.
TECH TIPS
- Dry stock farmers: think ahead about annual fertiliser requirements for the coming season. Your PGG Wrightson Technical Field Representative is a valuable resource.
- Monitor crop growth: keep an eye out for visual deficiencies. When discovered, refer to soil tests and take a herbage test. If herbage test shows nutrient deficiencies, consider the time of the season, weather conditions, and crop stage before evaluating the need for nutrient application.
