TRACTOR TO THE RESCUE
6kgN/tonne at 50pc availability, results in 120 units/acre of available nitrogen, meeting the total requirement of a spring barley crop for instance. Apply 80 or 100 units of chemical N along with this, and the harvest would indeed be a chore.
Problems
So the application of manure is not an exact science. The trick is how to work with this variability. For a crop like spring barley that is responsive to early nitrogen, it is a real problem.
Decisions have to be taken early in the season and the implication won’t be seen until much later in the season.
Organic nitrogen is made available to the crop according to the whims of soil bacteria, and these are not pushed around too easily, so it is hard to predict how they will perform over a given season.
The best balance is to under-feed a crop early in the season, in the hope that the nitrogen from organic manures will kick in later on and save the day.
Some years this won’t happen and the crops will suffer, in terms of yield and quality. In that situation, there may well be the opportunity to apply some late nitrogen to try and rebalance the book somewhat.
However, if you ignore the potential from the organic ma- nure and apply all the required N in chemical form, trouble will ensue.
The crop takes up far too much N, especially late in the season. The crop will also be far too luxuriant and thick and will lodge, which will have an impact on yield, quality and driver temperament.
Late nitrogen is difficult to apply, but not half as difficult as taking it off. When you are applying valuable organic manure to spring crops, ease off on the bag a bit — your combine will be eternally grateful.
Richard Hackett is an Agronomist based in North County Dublin and is a member of the ITCA and ACA.