Agronomy Advice

A Fine Balance between Quantity and Quality

Not so long ago, a three cut system used to dominate but in recent years we’ve seen farmers shift to a four and even five cut system. But why have we seen that shift?

farmer in a field checking the crops
farmer in a field checking the crops

Whilst three cut silage systems can yield extraordinarily well and produce good quality silage, they do require higher inclusion rates of concentrate feed to balance milking cow rations. By moving to 4 and 5 cuts per season, silage quality improves because you’re cutting grass with a higher leaf to stem ratio. There are some drawbacks, such as higher machinery costs with cutting more frequently and there can be lower overall DM production, but in general the advantages outweigh the disadvantages. Milk from forage figures improve as well as herd production and health as forage makes up a greater proportion of the ration.

A trial conducted in Northern Ireland a few years ago, comparing 3 cut and 4 cut silage systems, found total silage dry matter (DM) yields for the 3 and 4 cut system were 13.4 t DM/ha and 12.3 t DM/ha respectively. The average DM of the 3-cut system was 31.9% and 34.4% for the 4-cut system. The average metabolizable energy (MJ/kg DM) was 10.7 and 11.3, and average protein (% DM) was 14.3 and 16.4 for the 3 and 4 cut system respectively.

Cows on the 4-cut system had higher silage intakes (+9.5%), produced more milk (+6.4%) with higher milk protein (+2.1%) but slightly lower fat content (-2.4%). Silage production costs were calculated as £114 and £135 t/DM for the 3 and 4-cut system respectively. This includes a land charge, reseeding cost and a contractor for harvesting.

Total feed costs of 23 pence/cow/day higher with the 4-cut system, but the value of milk produced was 71 pence/cow/day higher. The margin-over-feed cost was 48 pence/cow/day higher for the 4-cut system. At the time this was calculated for a 100 cow herd over a 180 day winter period, the 4-cut system resulted in a £8,640 increase in margin-over-feed costs.

Fertiliser application advice

To give your growing grass just enough fertiliser to flourish, whilst maximising nitrogen use efficiency and saving on input costs, we would recommend that you plan how much nitrogen is required to grow this 3rd cut efficiently. You’ll want to apply 70-80 kg of nitrogen per hectare on 3rd cuts. The lower end of this range for shorter growing periods and upper end of this range with longer growing periods.

But don’t forget to take into account any slurry applications. To calculate how much nitrogen you’re likely to apply through your slurry you can do one of three things: (1) use RB209, (2) use a slurry analysis taken earlier in the year, or for the most precise calculation (3) undertake a new slurry analysis to calculate exactly how much nitrogen is present. Once you know how much you’re able to apply through your slurry, you’ll know how much mineral nitrogen fertiliser you’ll need to top it up with. Remember sulphur is a key nutrient on these crops to optimise nitrogen use efficiency.

Spread your slurry straight after you’ve taken your third cut and then follow that up with your mineral fertiliser six days later. If you’re worried about your input costs, don’t forget to use AHDB’s grassland cost benefit fertiliser calculator to protect your return.