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Tackling Soil Fertility on Your Farm

08 February 2023
Type Media Article

Damien Gibbons, Walsh Scholar, Teagasc Ballinrobe

The last 18 months have brought around exponential increases in the costs of production for many farmers resulting in adverse impacts on farm profitability. Looking towards the coming year early indications suggest that no great reductions in fertiliser, meal and fuel costs are going to appear on the horizon, as various geo-political obstacles are still at large.

Photo of someone taking a soil sample

Bearing this in mind, it is critically important farmers try and ensure they are as efficient as possible when it comes to farm operations. Soil fertility is the cornerstone of farm production systems and is a key area that farmers should look to address. Not only is adequate soil fertility needed for increased production efficiency, but more stringent environmental regulations (amendments to Nitrates Regulations) and high-input costs are two factors that are also driving this need.

Soil Sampling

Soil sampling is the first step in rectifying any soil fertility issues on your farm. As Peter Drucker once said: ‘you can’t manage what you don’t measure’. Taking a representative soil sample every 2-4ha gives the true nutrient status of the soil you’re working on. While soil samples can be taken all year round, the most favourable time to sample is between November and February. The next few weeks is an opportune time for farmers to sample before slurry and chemical fertiliser applications. Further information on soil sampling can be found at: Soil Sampling

Some noteworthy soil sampling requirements for 2023 include:

  • all successful ACRES applicants will require soil samples to be taken
  • soil sampling is mandatory for farmers stocked at >130kg N/ha (if they wish to apply phosphorus fertiliser. If no soil samples present, farm is assumed as Index 4 for P, which means the farm has no P allowance)

Soil Fertility

Productive soils are key for growing quality forage – whether it be in the form of silage for winter feeding or grass during the grazing season. If there is good quality grass fed, input costs (e.g. concentrates) can be reduced which ultimately leads to more money in your back pocket. To measure soil fertility we test soil to identify the pH level, Phosphorus (P) level, and Potassium (K) level. Soil P & K levels are classified into an Index scale 1 – 4.  For grassland, the optimum pH level is 6.3-6.5 and Index 3 for both P and K. Analysis conducted by Teagasc on national soil fertility trends in 2021 indicate that only 16% of all soils are at the optimum pH, P and K levels. As a result, most soils would be very responsive to targeted applications of lime (to increase pH) and compounds/straights/manures (to address P and K deficiencies).

Correcting soil pH is the first step in optimising soil fertility. The pH level of soil is hugely important as nutrients (N, P and K) may only become available to the grass plant at certain pH levels. Ground limestone is the most cost-effective way (approx. €25-30/tonne delivered & spread) to correct the pH and application rates are determined by a recent soil test report. If the lime requirement is greater than 7.5t/ha or 3 t/ac, it should be split into two dressings in year 1 and year 2. Ideally apply lime onto bare ground. August and September can be suitable times to apply lime when ground conditions are still good, silage is made and grazing rotations have lengthened.

The next step in correcting soil fertility is bringing the P and K levels to Index 3. Phosphorus is very important for root development, whilst Potassium increases stem strength and crop yield. When at Index 3 for both P and K, nutrients being removed in products (meat/milk) need to be replenished to maintain the optimum levels. Index 1 and 2 soils have a very low nutrient supply and require additional fertiliser/manure applications annually to bolster fertility levels, especially if carrying high stocking rates. Index 4 soils have a high nutrient supply. They present an opportunity to utilise the excess P and K reserves for crop establishment by reducing the need for fertiliser input thus saving money. Organic manures (slurry/farmyard manure) are a valuable source of N, P and K and can be effectively used to address P and K levels at targeted rates. Organic manures are best applied to fields that have high P and K requirements such as silage ground.

If you require any further information on soil sampling, soil fertility and fertiliser plans contact your local Teagasc office.