Agronomy Advice
March 22, 2024

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.

Spreader on a field

 A rule of thumb for cattle slurry is that 1,000 gallons contains 9 units of available nitrogen (N), 5 units of phosphorus (P) and 32 units of potassium (K).  

The NPK nutrient requirements of a 1st cut silage crop depending on the quantity of silage required and the swards yield potential, will range between 80 – 100 units/acre of N, 16 units/acre of P and 72 units/acre 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: 2,000 gallons/acre of slurry is applied, contributing 18 units/N, 10 units/P and 64 units/K. Nitrogen fertiliser required is 80 – 100 units/acre depending on silage demand and sward potential, fertiliser P 6 units and fertiliser K 8 units. 

For this example, we would recommend 3 – 3 bags/acre of YaraMila ExtraGrass. 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 1st cuts needs to be carefully considered, because of its implications on both these two factors. Dropping the N rate from 100 to 80 units/acre could 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 acre basis, by optimising the yield you can reduce the overall cost per tonne.

Where manures don’t cover the K requirements of your 1st cut, apply an NPKS product as trial work has demonstrated responses of 30 kg of grass per kg of K. A 1st cut can remove upwards of 100 units/acre which can deplete soil K reserves quickly. 1st cuts have the highest response to applied nutrients and are most likely to be your best quality silage, and this is why 1st cuts offer the greatest economic return when grown optimally.