ARTIFICIAL FERTILISER prices may have risen in recent months, but when used efficiently in combination with other nutrient sources, such as slurry, it will still give an economic benefit.
While it”s difficult to quantify an exact return from applying artificial nitrogen, fertiliser consultant Peter Hoey of Fieldfare Associates says it is generally accepted nitrogen achieves the best response from any input bought for the crop.
However, effective slurry use, soil nutrient testing, increased clover content of swards and smaller, more frequent fertiliser applications can all help reduce reliance on bagged fertiliser. “A spring dressing of 80cu m/ha of cow slurry contains nitrogen worth 36, phosphate worth 15, and potash worth 54, a total fertiliser value of 105/ha,” reckons Mr Hoey.
To make maximum benefit of this value, slurry should be spread early in the year to give grazing grass an early boost, suggests Ian Browne of the Farm Consultancy Group.
But grazing consultant Tom Phillips of Pasture to Profit prefers to see slurry used to dress silage aftermaths. “Using slurry on grass is essential to lower artificial fertiliser costs, but using it before spring grazing may not be the best way to use it.”
When spreading slurry, it”s also essential to spread it evenly and avoid excessive ground poaching or soil compaction, reckons Mr Browne. “Umbilical systems are best for ensuring even applications.”
But while agreeing better use of manures can often be made, Mr Hoey cautions against so-called fertiliser holidays. “For nitrogen this would be unrealistic and for phosphate and potash it is best to formulate a policy based on soil tests for each field.”
And soil isn”t the only thing which should be tested, according to David Munday of Creedy Associates. “Testing slurry will help make better use of it, as knowing what nutrients are available means you can account for them when planning bagged fertiliser applications.
“Where slurry is being used on maize ground it should be incorporated immediately to limit nitrogen losses to the atmosphere. And when applying to grassland it is best to use a trailing shoe or injection method to help prevent losses.”
While he questions the value of testing slurry nutrient values for typical applications on grassland, Mr Browne recommends regular soil testing to assess residual nutrients. “Winter is the ideal time to test, as there have been no applications to distort indices.”
To reduce reliance on bought-in nitrogen without yield penalties, Mr Phillips also advises making best use of other nutrients, such as phosphate, and increasing sward clover content to lift the amount of nitrogen fixed from the atmosphere. “The aim should be to use less than 100kg/ha of nitrogen a year on grassland.”
When planning applications, Mr Browne reckons frequent, small applications yield the best results. “When rotational grazing, it is best to apply a little fertiliser after each grazing. The aim should be to apply about 25 units/acre every three weeks, keeping the sward young and leafy.”
But after mid-June it is better to apply fertiliser as and when needed, adds Mr Phillips.
While some may question the cost of frequent spreading, Mr Browne reckons the time taken is good value for money. “Once you are in a routine, it doesn”t take long,” he adds.