Guest Blog: UpStream Thinking Nitrogen Results

September 30, 2013

Nitrogen, results so far from the UST project

Nitrogen (N) has been a problem in the South West Water (SWW) boreholes for many years. As part of the UpStream Thinking project (UST), FWAG and WRT (Westcountry Rivers Trust) have investigated the sources of N, also advising land owners of win win scenarios that would contribute to a reduction in N loss. 

What we did

Ten fields were selected on ten separate farms (thanks again to those involved), spread between the mouth of the River Otter to the A30. These fields covered all the major land uses in the area, including; cereals, high/low input grassland, maize/cereal stubbles, outdoor pigs, clover etc. For three winters (2010/11, 11/12 & 12/2013), each field has been tested pre and post winter for nitrogen levels. The data captured gives an indication of potential N losses over the course of the winter and is used to inform and help land management.

Results

Samples were taken at 3 depths, 0- 30, 30- 60 & 60- 90 cms. The graphs below indicate a decline in losses over the past three winters. It is important to caveat this work due to the variability of N and also the other variables that influence decision making, cost, crop, weather etc. but the overall trend is down. Field 4 is interesting, in 2010/11 there was a flush of N into the system, followed by a large loss in 2011/12 and finally a smaller loss in 2012/13. This is a organic field that started as high clover grassland before going into several years of arable. N (in Nitrate form) within groundwaters is undesirable, irrelevant of its source, natural or man-made.

Other nitrogen testing carried out by the UST project indicates that heathland with high concentrations of gorse can have the potential to lose the same amount of nitrogen as overwintered cereal stubbles.

Note: During winter 10/11 total losses from all 10 fields came to 11 tonnes (worth £3,648) of bagged nitrogen!

Conclusions so far...

It’s not surprising, but the results do show that certain landuses have greater risks of N leaching than others. e.g. outdoor pigs leave a significant amount of N in the soil profile. They have a high protein diet, but there is little/no vegetation cover to capture the waste N before it leaches. Root crops can also leave high residual N. Many underestimate the amount of N applied in manures before applying additional bagged fertiliser. Plus there is still over application on some grass and cereals, though testing results have influenced land management, several cases have seen reductions in lossess and quantities applied.

With thanks to: Iorwerth Watkins, Westcountry Rivers Trust

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