Ensuring optimal soil fertility is critical and to do this farmers need to ensure lost nutrients are replaced.
Removal of hay or silage takes large amounts of nutrients from your soil with nutrients needing replacement for ongoing pasture quality and productivity.
Nitrogen is removed in the greatest amounts, followed by potassium and phosphorus (see Table 1). Hay removes less potassium than silage as it is harvested at a more mature stage when herbage potassium levels are lower.
| Nutrient | Hay | Silage |
|---|---|---|
| Nitrogen (N) | 20 | 20 |
| Potassium (K) | 15 | 20 |
| Phosphorus (P)) | 4 | 4 |
| Sulphur (S) | 3 | 3 |
| Magnesium (Mg) | 2 | 2 |
If hay or silage is fed out where it was grown some nutrients are unevenly distributed back into the soil via dung and urine, but if it's fed out elsewhere or exported off farm all its nutrient value goes with it.
Either way, nutrients need to be replaced, in addition to regular maintenance fertiliser requirements. Paddocks that continue to be cropped without doing so can deteriorate over time and become vulnerable to undesirable species such as flat weeds, brown top and poa.
Potassium, removed in the greatest amounts after nitrogen, is especially important for post-harvest clovers, which take some time to recover from being shaded out by grasses. If any nutrient is in short supply clovers suffer first as their root system is shallower than ryegrasses', making them a poorer competitor for nutrients. Lack of potassium can easily limit clover growth, which in turn can affect longer term pasture production and quality and nitrogen supply.
Soil testing annually provides an accurate picture of soil fertility status and nutrient requirements. Herbage analysis is also useful when multiple cuts are taken from a crop.
If Olsen P levels are optimal (20-30 for ash and sedimentary soils or 35-45 for pumice and peat soils) maintenance phosphorus can be applied at any time. If Olsen P is below optimal, apply phosphorus when the paddock is shut up.
If a Quick Test K is under five, apply potassium before the paddock is shut up, otherwise apply it post-harvest. Post-harvest potassium applications can be split if large amounts of potassium are required to replace potassium removed and/or achieve the desired soil test range, or if winter leaching is a risk.
Avoid over-applying potassium, as growing plants take up excess potassium without converting it into extra growth, elevating herbage potassium levels. This could reduce the return on fertiliser investment if potentially elevated potassium herbage levels in conserved feed and/or re-growing pasture are removed as hay or silage is harvested.
Ensure sufficient sulphur is applied annually, and magnesium may also be needed if soil test levels are below optimal (8-10). Molybdenum can be checked via herbage testing and applied as required.
Nitrogen is best added 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 nitrogen together with maintenance fertiliser after each cut, aids recovery and improves the yield of the next cut.
To give you some idea of what's involved, a silage crop yielding 3 tonnes (t) of dry matter per hectare (ha) will remove around:
- 12 kilogrammes (kg)/ha of phosphorus (or 4 kg/t)
- 60 kg/ha of potassium (or 20kg K/t silage/balage)
- 9 kg/ha of sulphur (3 kg S/t dry matter for silage and hay) and
- 6 kg/ha of magnesium (Mg 2 kg/t dry matter silage and hay)
Suitable products include Pasturemag® Hay & Silage, which has been developed to replace nutrients removed in hay and silage and supplies N, P, K (as well as S, Mg, and calcium).
Pasturemag® 10K is a general fertiliser which supplies N, K, P, S and Mg and calcium and is typically applied at 500-600 kg/ha.
For more information contact your local Farm Source TSR.
Article supplied by Ballance Agri-Nutrients.