Variability in slurry results shows benefit of analysis in Wales

Variability in slurry results shows benefit of analysis in Wales

Friday, June 13, 2008

Standard 'book figures' are a good starting point when it comes to making an assessment of the nutrients supplied from slurry. However the samples taken ina recent project showed a massive variability in nutrient content, depending on storage conditions and feeding regime. This variability, ranging from 20% to over double the book figures, emphasises the value of sampling and analysing your own slurry, says Chris Duller of the Grassland Development Centre, IBERS.

The project carried out by the Institute of Biological Environmental and Rural Sciences' Grassland Development Centre at Aberystwyth University for the Dairy Development Centre based at Gelli Aur, Carmarthen, helped 200 dairy farmers in Wales address how they target both slurry and fertiliser nutrients to their land. It was supported by European Union Objective One funding.

It also revealed a large variability in soil nutrient status. Over 40% of soils were above target index 2 for phosphate, offering opportunities for reducing purchased phosphate fertilisers. Almost 50% of soils were deficient in potash (below index 2+), which would be restricting silage yields.  Only 30% of all soils sampled were in the target pH range for optimum grass and clover growth (6-6.5).

With ever increasing prices, there will be many difficult decisions to be made about the most cost effective ways to grow grass. This, coupled with the threat of NVZ legislation impacting further in Wales, makes it essential that farmers think more carefully about how they store and utilise their slurry to maximise the amount of nutrients that go back into grass growth.

When analysing slurry nutrients it is vital that the sample is representative of what is actually spread, explains Chris. "Taking a sample from a well stirred store or even from the tanker in the field are the recommended options. Grabbing a sample from the yard or from the reception pit is not going to give a meaningful result." 

"Working out how much fertiliser a silage crop needs after it has had a dressing of slurry is a decision that almost every conventional farmer in Wales has to make. Getting it wrong can either mean losing out on yield by not providing enough nutrients, or oversupplying nutrients which will be an economic waste, a potential source of pollution and could lead to a poor quality fermentation. However, knowing soil nutrient status, slurry nutrient content and application rate it is fairly easy to make an accurate assessment of what is needed from bagged fertiliser to optimise grass growth and quality. This project was all about providing quality information on which to make sound business decisions."

Further information is available from Grassland Development Centre, IBERS, Aberystwyth University 01970 823026 / Dairy Development Centre 01554 748570.

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