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Accuracy over Precision Farming

Last updated: 20 Jul 2015


Precision farming gets a lot of interest and rightly so but ‘precision’ isn’t the whole story. Accuracy is what’s needed and precision is just part of that. For example, in darts, precision could be hitting exactly the same point every time - even if this is at the edge of the board. Accuracy would be getting close to the bull every time - even if the darts were a bit more widely spaced. The darts are thrown less precisely but more accurately. For accuracy, we need to know what we’re aiming for and to get as close to it as possible, accepting that we’ll never be perfect.

In nutrient management, accuracy means having a clear idea of what needs to be achieved, and why, and getting the basics right before moving to higher technology. The latest annual report from the Professional Agricultural Analysis Group (PAAG) illustrates this.

In 2013/14, of 130,000 soil samples from arable land only 10% were at target indices for both P and K.

27% of samples were below target for P and 43% above.

31% were below target for K and 38% above.

12% of samples were below target for both P and K.

Things were similar in samples from grassland where 9% were at target indices for P and K.

36% were below target index for P and 41% below target for K.

Overall, 90% of samples indicated scope for improvement by adjusting soil index. It takes time to change an index so you might think things are improving but have yet to achieve perfection. Not so – PAAG reports from 2009 indicate no improvement, in fact just a drift downwards in indices, especially in grassland. There’s been a drift down in soil pH too. In 2013/14, pH was lower than 6 in 20% of arable samples and lower than 5.5 in 21% of grassland samples. There is plenty of scope here for improving accuracy of nutrient and lime use without any high technology, by just getting the basics right.

Field margins is another area where accuracy is needed. The new GAECs 1 and 7a in 2015 specify no cultivation or fertiliser application within 2m of surface water and no manure within 10m of surface water unless precision equipment is used. Precision certainly is essential to avoid non-compliance but for accuracy it’s also necessary to know what the real objectives are. The aim is to prevent nutrients, especially phosphate, from getting to the water and but even narrow buffers can provide a habitat for beneficial insects including pollinators and predator insects. The amount of phosphate trapped might not be important economically (though SRUC has been assessing different plant species for their ability to scavenge phosphate that can be returned to the field) but any increase in pollinator or predator insect numbers will be. Precision equipment for slurry spreading – trailing shoe, trailing hose or shallow injection – will permit spreading to within 6m of a watercourse but also will save economic amounts of nitrogen from loss to the air. The objective in using this equipment is not just to comply with a rule but to reduce the loss of nitrogen so saving money.

Accuracy in nutrient management needs more thought than precision does. Objectives need to be clear and costs and benefits quantified. Appropriate farming practices need to be identified and put to use. The intensity of management needed for good control of nutrient supply is demanding but the benefits will repay it.