5 steps to take now and improve soil fertility for next year

Phelim Connolly

There is often the temptation to purchase the same chemical fertiliser annually that has been historically used on farm. 

However, without understanding our soils fertility many local farmers may be needlessly spending extra money on compound fertilisers that are not required.

A recent analysis of 6,343 soil samples taken from grassland and submitted by Business Development Group (BDG) participants showed that only 439 or approximately 7% of samples were at optimum levels of soil fertility. The remaining 93% of samples were either deficient in lime (pH), phosphorus (P) or potassium (K).

Many studies have shown that achieving optimum soil fertility will lead to greatest grass growth potential and help reduce the overall cost of production, whilst also protecting our environment.

How can you start to improve soil fertility?

Step 1 – Soil test

The months of November, December, January and February are ideal months to soil sample, provided no chemical fertiliser or organic manure has been applied in the previous three months. These samples will advise you on your lime, P and K requirements for the 2020 grazing season.

Step 2 – Soil PH

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Apply lime, if required, at your first available opportunity. Your soil analysis results will recommend the amount of lime required. In high rainfall areas, lime can be depleted more quickly from soils. If soils are too acidic, they can lock up the value of other nutrients and trace elements within the soil, particularly nitrogen and phosphorus.

If lime is spread first, leave at least three months before the application of slurry or standard urea, so that there is no loss of nitrogen to the atmosphere.

However if slurry or urea are spread first lime can be applied after one week. Studies have shown that protected urea can be spread after lime application without any loss of nitrogen to the atmosphere.

Step 3 – Phosphorus (P)

From the 1st of January 2020 all farms applying chemical P fertiliser will need to demonstrate a crop requirement. If your soil analysis results are showing P levels of index 3 or above there is no benefit spreading chemical fertiliser which includes phosphorus as the soil is already at optimal levels. Continuing to purchase fertiliser compounds that are not required is a waste of money and potentially impacting on water quality. If soils are showing optimum levels for P, then slurry or organic manures high in phosphorus should be spread on land which does show a requirement.

Step 4 – Potassium (K)

Potassium is critical for the uptake of nitrogen and other nutrients by the root system. Grassland regularly cut for silage can become deficient quite quickly. This can be addressed by application of slurry or farmyard manure and any remaining requirements can be addressed using chemical fertiliser.

Step 5 – Balance

It is important to try and balance all of the above nutrients. If soil is deficient in one nutrient it will inhibit the uptake of another. Therefore regardless of how much additional nitrogen is applied it may still not be utilised effectively.

Phelim Connolly is an agri-environment adviser, based in Enniskilen with CAFRE

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