Tillage: Organic fertilisers are the only way to rejuvenate old soils
Published 07/10/2015 | 02:30
The closed period for organic fertilisers starts on October 15 for slurry spreading, and on November 1 for farmyard manure (FYM). So the next few weeks are the final opportunity this year to spread.
Organic fertilisers are really the only way to rejuvenate old tillage soils. Not alone will they provide the major nutrients but they also provide a wide range of trace elements and organic matter.
We normally put a economic value on slurry of €25 per 1,000 gals (slurry) and €10 per tonne (FYM) based on the units of nitrogen (N), phosphorus (P) and potash (K). Pig slurry has a higher P and lower K concentration than cattle slurry, so it should be prioritised to land with the lower soil P levels.
Poultry manures are worth at least €30/t and spent mushroom compost €10-15/t. Treated biosolids (the organic byproduct of urban waste water treatment) vary widely in value depending on the type of treatment and nutrient content.
Yield improvements following a few years of organic manure application cannot be explained by the nitrogen, phosphorus and potash content of the slurry/farmyard manure, which muddies the guideline economic values of the materials.
The additional yield is probably attributable to the increased organic matter, improved biological activity and additional trace elements.
Current cereal prices are making us more and more cost conscious, but the risk is that savings will be attempted that put the economic yield at risk. A classic example is the on-going fall in both soil P and K levels on many farms.
This year's higher yields have resulted in greater nutrient removal. The standard advice is that for every tonne of winter wheat or barley harvested, and the straw taken off, 3.8kg P and 9.8kg K is removed. Oats will also have removed 3.8kg/t of P, and even more K at 14.4kg/t.