Farm Ireland

Monday 10 December 2018

Don't miss the chance to apply a good dose of organic manure on depleted tillage soils

Stock Image.
Stock Image.

Richard Hackett

It's definitely not going to be an early season. There is a lot of work to be carried out and ground conditions are slow to come around.

Winter crops will shed their winter coat very quickly and it is important to have available nutrients close to them to allow them start off again. Spring crops will need to get into the ground before they can start their cycle.

The build-up in work pressure will need to be managed. Many had plans to make use of organic manures before planting.

This is especially so this year given the longer than normal winter that many livestock farms have had to endure, resulting in plenty of organic manure now looking for a home.

However, waiting to apply manure before ploughing in an already delayed season may add more time pressure to an already pressurised system. Don't write it off though.

Provided that there is not an undue delay in waiting for applications to the land, a few extra days delay in sowing will be well worth it in most situations.

Given the depleted state of our of tillage soils, organic manures bear dividends way over and above their 'paper' nutrient contents. This is particularly true for soils normally in winter cropping and planned to be back in winter cropping in the future - here the opportunity to apply a good dose of manure should not be dismissed lightly.

The gain to the soil will bear long term dividends even to the point where delaying establishment of this crop to get organic manure could impose a yield penalty this season.

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One aspect that is not fully taken into account when applying manure is the actual nitrogen content, especially in some of the lower N content manures such as farmyard manure or spent mushroom compost.

According to the new nitrates regulations from 2017, farmyard manure contains 4.5 kg N/tonne.

The availability of this nitrogen is given at 30pc. Therefore an application of 25t/ha farmyard manure gives 112kg N/ha or 33.75kg available N /ha.

That's 27 units/acre in old money or a bag of CAN per acre. However, these are average figures and the 30pc figure is not written in stone either. Another figure often open to question is the 25t/ha.

So where the plan is 25t/ha or 10 t/acre, areas may well get well over this amount.

Manure can contain a lot or very little straw. Obviously, manure with lower levels of straw will have a higher nutrient content than high levels of straw.

Where the manure is incorporated well and soil temperature and soil moisture are high, the availability can be much higher than the 30pc.

A combination of these factors could lead to some very high levels of available nitrogen from farmyard manure. Applying 50t/ha at a figure or 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.


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 manure 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.

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