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Ian's Blog on PAAG report 2013

Last updated: 30 Dec 2013


Hand and soil_170_142


It’s about five years since the main UK laboratories set up PAAG (Professional Agricultural Analysis Group) to help ensure consistent results for soil analysis. Since then, PAAG members have taken part in ring-testing for routine soil analysis (pH, P, K, Mg) administered independently by Wageningen University. PAAG also produces annual summaries of soil testing results in reports that can be seen at the Tried & Tested web site. The report for 2012/13 makes interesting reading. It summarises results for some 250,000 soil samples taken throughout the UK, breaking these down into arable and grassland.


Soil pH was below 6 in 19% of arable samples and below 5.5 in 19% of grassland samples. So it looks as if a fifth of agricultural land could do with some lime. Of course this is about the proportion expected for the typical liming interval but pH wouldn’t usually get so low.  When the British Survey of Fertiliser Practice shows that less than 10% of arable land and 3% of grassland received lime in 2011/12, it might be time for back to basics and getting soil pH sorted out.

maize field_275_183Mg index was 0 or 1 in 16% of arable samples where responsive crops need an application but in only 3% of grass samples. There’s also scope for improvement in phosphate and potash – I know, it’s boring but P and K are the foot soldiers in the nutrient world and, if you want to win, you can’t do without them. 29% of arable samples were below target index (2) for P and 33% were below target index (2-) for K. Yield is at risk in the fields these came from. Index was above target for P in 43% of arable samples and for K in 37% of arable samples. Savings might be made in these fields. Only 9% of arable samples were at target index for both P and K so in around 90% of fields there could be improvement. It must pay to check phosphate and potash use and adjust where necessary. The situation is very similar for grassland – 34% of samples below target index for P and 41% for K with 36% above target for P and 32% for K. As with arable, only 9% of samples were at target index for both P and K.


Putting things into perspective - the typical cost of soil analysis works out at about 20p/ha/year and it’s covered by less than 2 kg of grain. Then just a 1% loss of wheat yield costs around £17/ha. Also, don’t think you’ll spot when a lack of phosphate or potash starts to affect yield. It’s rarely possible to see any difference in two crops growing in adjacent plots when one eventually yields 10% more than the other. When you don’t have the comparison, you have no hope of detecting a sizeable yield loss. You could be losing £170/ha without knowing it.

The answer is easy. Treat phosphate and potash like nitrogen and base their use on crop need, not just on cost saving.