SEEING FLEDGLING winter wheat and barley crops acquire a hint of brown this spring does not necessarily send Philip Huxtable, technical director at JSR Farms, reaching for the sprayer and a dose of fungicide.

Any discolouration is not caused by an attack of foliar disease, but by the application of separated slurry from the east Yorks farming operation”s pig units.

 “We”ve always put slurry and farmyard manure on autumn stubbles,” says Mr Huxtable.

 “But over the past 10 years we have applied a bit of science to use separated slurry as a spring fertiliser.”

 The solid fraction from the separator is mixed with farmyard manure to help what is little more than wet straw rot down to a material that can be ploughed into stubbles in the autumn. Investment in storage and application capacity makes the liquid fraction available for crops in spring and early summer.

 “We store as much separated slurry as we can, waiting for crop and ground conditions to come right,” he says. “It mainly goes on to winter wheat, but, when conditions allow, there is no reason not to start on winter oilseed rape in late February, before moving on to the winter wheat and spring barley, which takes us right through to early May.”

 On most farms, the “dirty water” can be pumped from pig unit storage tanks through a network of underground irrigation mains to hydrants connected by umbilical hose to a tractor-mounted applicator. This winter, a storage tank was erected on a farm with no livestock.

 “We have seen such a difference in crop performance over the years that we realised this tired farm needed its fertility improving by organic means,” says Mr Huxtable. “We”ll certainly be putting on separated slurry and if we can find a way of economically transporting farmyard manure to the farm, it will get that, too.”

 Routine nutrient analysis at the time of application is essential because of the separated slurry”s inconsistent nutrient content.

 “We see considerable variability between pig units because of diets, between stores because of dilution and from top to bottom within storage tanks,” notes Mr Huxtable. “The contents are mixed before and during application and frequent samples taken to accurately calculate the nutrients supplied.”

He says an experienced user can analyse a sample using the 200 Quantofix instrument in about five minutes. ADAS Manner software is then used to calculate how much of the nitrogen is available to the crop.

As an example, he cites a set of results showing 7kg of nitrogen and 2kg each of phosphate and potash per cubic metre of separated slurry. Based on the dry matter content and crop growth stage, the software indicates that 75% of this nitrogen would be available, which, at 13cu m/ha, amounts to 70kg/ha, worth 22/ha at 110/t for bagged N.

 “The value of phosphate, potash and sulphur in the separated slurry can be more than 20/ha, so overall we are looking at a total saving of at least 40/ha,” he enthuses.

 “At the other end of the scale, we might have as little as 1.5kg cu m of nitrogen, in which case we would be looking at using 50cu m/ha, still within our self-imposed limit to minimise any pollution risk from slurry seeping into drains and dykes.”

 Previous hose-reel irrigator applications proved too slow, so now an umbilical system, with a flexible hose feeding a 24m (40ft) wide tractor-mounted low-level splash plate applicator is used. It can cover as much ground in a day as the irrigator could in a week.

 “Physical damage from the hose restricts applications on oilseed rape, but in cereal crops we go to Growth Stage 31, second node, although crops will recover from applications made up to GS32,” says Mr Huxtable. “We don”t have a heavy tanker causing soil compaction and if the wind gets up, we can fold the boom to 12m (20ft) and use dribble tubes to put the slurry directly on to the surface.”

fwmachinery@rbi.co.uk