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Vital to know how much N is in the soil

Measuring how much Nitrogen crops will get from the soil is more than just helpful, it's essential, according to leading arable farmer Andrew Ward.

Andrew Ward manages the 650ha all-arable Roy Ward (Farms) business near Leadenham in Lincolnshire and also runs his own cost analysis and advisory service WCS (Ward Cultivation Solutions). In his opinion the GrowHow N-Min test is a vital part of cost effective farming. "I cannot understand why more people are not using it," he says.

Andrew's confidence in the N-Min & N-Calc service is based on firsthand experience. Unlike a basic SMN (Soil Mineral Nitrogen) test which simply measures how much N is in the soil on the day the sample was taken, N-Min also calculates the AAN (Additionally Available Nitrogen). This is the N which will become available to the crop from the soil through mineralisation during the growing season.

And make no mistake there can be some wide variations in the amount of N a crop can expect to get from the soil. GrowHow company agronomist Allison Grundy explains. "In Lincolnshire we've had N-Min values as low as 50 kgN/ha and as high as 150 kgN/ha after WOSR, in the same season on similar soil types," she says.

N-Min provides an accurate measure of what the crop will get from the soil and can be conducted anytime from now through to the end of March provided no fertiliser has been applied But calculating the optimum N rate for the Nitrogen Management Plan also requires other information.

Andrew continues, "In oilseed rape some farmers are now using the GAI (Green Area Index) but assessing N requirement by GAI alone is not good enough, you must also take account of soil N and that's where N-Min comes in."

Allison agrees: "The amount already taken up by the crop and the Soil N go hand in hand. Together they are known as the SNS (Soil Nitrogen Supply)."

The final pieces in the jigsaw are yield and quality expectations. "It is essential that farmers are honest about their expectations," adds Allison. "Predicting a 10 tonne crop when you know 8.5 is more likely will result in over application whereas being too conservative will limit the crop's potential."

To take the pain out of all the arithmetic GrowHow has developed the N-Calc. This uses the N-Min result along with the farmer's yield and quality expectations and the soil Nitrogen supply to calculate the optimum Nitrogen fertiliser rate for cereals and OSR.

The table below shows the positive impact of the N-Min & N-Calc system at Roy Ward (Farms) in 2009. The financial benefits calculated by Andrew Ward ranged from £3.86/ha for winter wheat after spring beans to more than £50/ha in one of the oilseed rape fields.

Andrew has the last word: "N-Min tests cost around £100 which is really very little outlay, so don't skimp on the number of tests. You need two fields in each rotation as a minimum. If the N-Min comes back high, be brave and go with it but leave a small comparison to follow the farm standard - just to be sure," he advises. "Then simply stand back and watch the crop and your bank balance grow!"     

Farmers Weekly Arable Farmer of the Year 2008 and twice the Cereals event host, Andrew Ward, left, has put GrowHow's Nitrogen management system through its paces. Andrew is pictured with GrowHow Adviser Dave Towse in one of the trials last summer.

For further information please contact:
Allison Grundy, GrowHow UK Limited Tel: 0151 357 5611 or mobile 07850 295096
Email: allison.grundy@growhow.co.uk 
Helen Riby, Active Solutions Tel: 01623 656958 Fax: 01623 624167
Email: helen@activesolutions.uk.com

About GrowHow UK Limited
GrowHow UK Limited is the UK's leading manufacturer of ammonium nitrate and compound fertilisers.