Careful monitoring of phosphorus levels in grassland can boost yields by up to 12%, research by CF Fertilisers reveals.

Even at soil index 2, maintenance applications of P throughout the season provide a significant increase in yield. As conserved forage grown on-farm can provide cheaper feed than bought-in compounds, time spent getting a good grass crop this summer will make money next winter, says the company's farm adviser Hefin Llwyd.

Some people, seeing a soil index of 2, may be tempted to skip phosphorus applications and think it won't cause a big loss in yield," he explains. "But the results show that failure to apply phosphorus can mean farmers could see a reduction in silage yield.

Trials took place at Reaseheath College in 2014 and examined a three-cut system taken in May, July and September. All grass received the same nitrogen - 240 kg/ha split 90:90:60 for each cut. But different rates of phosphorus were used: 0, 80 or 120 kg/ha of P2O5 evenly split and applied at the same time as the nitrogen.


Deliver more feed - graph


Results from the trials are quite straightforward: at index 2, there is a yield benefit from a fertiliser manual based maintenance dressing of 80 kg/ha, but there was no additional benefit from applying 120 kg/ha

Hefin notes.

The yield increase was seen in May, July and September, and added together, the application of 80 kg/ha P2O5 resulted in an extra 1.24 t DM/ha being available to feed livestock, an increase of 12%. The extra feed provided by one hectare brings real financial benefits, according to Hefin.

Based on a triple super phosphate cost of £250/tonne, 80 kg P2O5 costs about £45. The actual feed value of the additional dry matter depends on the silage quality and how it is stored and used, but the figures show that most farmers can reduce their feed bill by getting phosphorus applications spot on, even at soil index 2.

For example, for silage containing 11.5 MJ ME/kg DM, an extra 1.24 t of silage dry matter delivers 14,260 MJ of ME.

You won't use all of this.

but if you make and store the silage well, you can expect 85% to be available which is around 12,000 MJ ME.The amount of energy produced could replace about £250 of bought-in feed, and is equivalent to over £500 of milk. So this isn't a case of marginal gains - the difference between £45 spent on phosphorus in fertiliser and £250 on feed is a healthy 5.5:1 return on investment.

Getting it right can make a real difference to the cost of production.

Key Facts:

What is the value of 1.24 tonnes extra dry matter?
It is 14,260MJ of metabolisable energy (11.5MJ/kg)
A good target of 85% of available energy so 12,121MJ are available to livestock which is:
2,245 litres (5.4MJ/l) of milk worth £516 (23p/l)
Maintenance plus 9.5 litres for one day for 100 cows
1.05 tonnes of high energy dairy cake, worth £246