Why slurry can deliver an extra €120/ac for tillage farmers on fertiliser savings and higher yields

Farmer spreading slurry in a field
Farmer spreading slurry in a field
PJ Phelan

PJ Phelan

Harvest yields are yet again proving the benefit of applying organic fertiliser to land. Some of that benefit may be coming from it's organic content but I suspect that much of it is coming from its nutrient content and rich microbiology.

Our nutrient management plans based on nitrogen and phosphorus limits may neglect potassium and trace elements. Animal slurries meet those requirements, even without any planning.

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The release pattern of nutrients from organic materials very much match plant growth - slow release when plant growth is slow and faster release as soil temperatures and plant growth increase.

Slurries improve soil biology resulting in improved breakdown of crop residues and enhanced nutrient release. The applications of 2,000 gals/ac of animal slurries (pig, cattle) give a saving of approximately €50/ac on fertiliser costs, depending on dry matter content.

That combined with an extra yield of perhaps 0.5t/ac of cereal is worth in excess of €120/ac.

In many parts of Europe intensive livestock producers pay tillage farmers to take slurry. Here livestock farmers do everything they can to spare their own slurry on their own land, even at soil P index 4.

From an environmental perspective it is preferable that some of that slurry be exported to tillage farmers.

That should be incentivised within schemes managed by DAFM. Perhaps the proposed mandatory use of low-emission slurry equipment by all farmers who exceed 170 kg N/ha should be withdrawn for all their slurry provided that the surplus over 170 kg/ha is exported to tillage lands.

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Tillage farmers have land available for slurry application during periods (February to April and July to October) when many livestock farmers have too much cover to apply slurry without damaging grass.

Tillage land also has the greatest need for slurry as cultivations have a huge effect on soil biology. We plough land cultivate it, dry seedbeds and in some cases compact soils - the home of earthworms and a whole range of bacteria and fungi (microfauna) which are not visible to the naked eye.

While macrofaunal populations do recover from soil disturbance, our soil management should prioritise that recovery. In recent years numerous soil biology enhancers have been developed for application to land yet the real answer lies with slurry.

While most people are aware of the importance of earthworms, who digest and transport organic material within the soil, and create drainage channels, the essential role of bacteria and fungi is less well understood.

Earthworms

Where soil pH is low earthworm populations are reduced and in the absence of worm channels in the soil drainage is restricted and soils become waterlogged. We are all well aware of yellowing effect of waterlogging on plant growth.

To produce healthy plants we need healthy soil and a healthy soil require microfauna. Beneficial microfauna thrive in free draining, warm and moist soils. Compacted or waterlogged soils suffering from poor air spaces within the soil, partially decomposed organic material or low pH are not suitable for most of the beneficial organisms.

Addition of slurry on field areas prone to waterlogging is not advisable.

In such soils nitrogen is converted to nitrite, a harmful greenhouse gas, and the nitrogen is lost for plant growth. Fungi and bacteria provide for the recycling of nutrients and the central agents in the sustainability of soils and crop production.

They grow on plant residues and produce enzymes that break down plant residues which in turn release nutrients. Those nutrients are then available to be taken up by plants. The soil microfauna are critical in the mineralisation of organic phosphorus to convert it to a form suitable for plant uptake.

The organisms also extract and store carbon which later becomes available to other organisms higher up in the food web.

Slurry is the answer to many of the problems that tillage farmers have in trying to achieve high yields and to improve soils.

Unfortunately, it is not available to all tillage farmers. In some cases, it only becomes available when a livestock farmer realises that he is going to be over his limit and appears, close to the deadline for application, with a request that the tillage farmer takes slurry from him.

Now is the time for livestock farmers to advise of slurry availability and indeed for tillage farmers to chase up their neighbours who appear at the last-minute requesting slurry exports.

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