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Over the coming days and weeks, it will be time to put a fertiliser shopping list together for 2018. There has been a considerable change to phosphorus (P) limits and how slurry is accounted for in the new Nitrates Action Programme (NAP) on grassland farms.
Therefore, a different fertiliser P mix will be required, especially for low-fertility fields.
Good soil fertility is an essential ingredient for both grassland and tillage soils, which is the driver of season-long grass growth and the production of high grain yields. Soil testing measures available soil fertility (pH, P and K) on your farm.
This will be the basis on deciding where slurry/farmyard manure is applied and which fertiliser blends are most suitable to build and maintain soil fertility in the optimum ranges.
Slurry has now been removed from calculating farm P allowance. This is a valuable source of N, P and K and should be recycled efficiently in the spring time to maximise N recovery and targeted to fields with the lowest P and K levels for efficient use.
There is a medium P and K demand on grazing areas of the farm as the majority of P and K is recycled back on to the pasture by grazing livestock.
Aim to apply 50% of P & K requirements once significant grass growth starts in the spring time. The ideal fertiliser blend for grazing ground is an 18-6-12 or 10-10-20 type product as it supplies both P and K in the correct ratio.
Slurry ideally should be recycled on the silage areas as it contains P and K in the correct balance for silage production.
Additional P
Under the new NAP the rates of P for index 1 and 2 soils have increased to facilitate the buildup of low fertility soils and increase their productive capacity.
Higher P rates are available on farms with the following criteria – a grassland stocking rate above 130kg org N/ha, soil test results for every 5ha and engage with a FAS adviser to complete a farm fertiliser plan.
Remember before applying additional P, correct soil pH to the optimum range of pH 6.3 to 6.5.
Example of farm P calculation
Take a 40ha dairy farm (with 65 cows and replacements) stocked at 170 kg org N/ha, with 80% of the farm at soil P and K Index 1 and 2 and 20% at Index 3, feeding one tonne of concentrate per cow.
It is assumed that all the slurry is applied to P index 1 and 2 soils to avail of 50% reduction P availability in slurry. In this example, the maximum farm P allowance is 1,938kg, which is a 50% increase in farm P allowance compared with 2017.
To determine actual P allowances for your farm, it’s important to contact your local adviser and have a farm fertiliser plan prepared.
Potassium (K) rates
Potassium is an essential nutrient for nitrogen uptake and efficiency. The silage ground will have the largest demand for K, therefore aim to recycle cattle slurry/FYM on areas that are cut for silage on the farm.
This is the most effective way to replenish especially soil K reserves.
If additional K is required for buildup, apply as MOP 50% K in the autumn. Grazing areas have a lower K demand which can be supplied by a suitable compound fertiliser.
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