Greater returns from first cut silage crops

Slurry applications in spring can make up most if not all of the NPK requirements of a 1st cut, so it’s important to do your sums before deciding on the rate and type of fertiliser needed in March.

A rule of thumb for cattle slurry is that 1 m³ contains 1 kg of available nitrogen (N), 1.2 kg of phosphate (P) and 2.5 kg of potash (K).

The NPK nutrient requirements of a 1^st cut silage crop depending on the quantity of silage required and the swards yield potential, will range between 100 – 120 kg/ha of N, 40 kg/ha of P and 80 kg/ha of K. By knowing the quantity of slurry applied, you can calculate the NPK contribution from your slurry using the values above. To finally calculate what fertiliser is required, just subtract the nutrient contribution from the slurry from the crop requirements for each nutrient.

Example: 20 m³/ha of slurry is applied, contributing 20 kg of N (20 x 1), 24 kg of P (20 x 1.2) and 50 kg of K (20 x 2.5). Nitrogen fertiliser required is 80 – 100 kg/ha depending on silage demand and sward potential, fertiliser P 16 kg/ha and fertiliser K 30 kg/ha.

For this example, we would recommend 320 – 400 kg/ha of YaraMila Stock Booster S. This true uniform compound fertiliser also contains sulphur which is necessary in many enzymatic functions and protein synthesis in grass, resulting in yield increases in the range of 10 – 20% and improvements in grass protein and sugar concentrations.

N drives yield but also grass protein levels. Reducing the N rate on 1^st cuts needs to be carefully considered, because of its implications on both these two factors. Dropping the N rate from 100 kg to 80 kg will likely decrease silage protein by 1% and lower the yield by between 1½ – 2 tonne of grass per ha. Since most of the costs associated with making silage are on a per ha basis, by optimising the yield you can reduce the overall cost per tonne.

Where manures don’t cover the K requirements of your 1^st cut, apply an NPKS product as trial work has demonstrated responses of 40 kg of grass per kg of K. A 1^st cut can remove upwards of 150 kg/ha which can deplete soil K reserves quickly. 1^st cuts have the highest response to applied nutrients and are most likely to be your best quality silage, and this is why 1^st cuts offer the greatest economic return when grown optimally.