Assess your soil fertility in six simple steps

Assessing your soil fertility is easy, according to Anthony O’Connor, Teagasc Adviser, Galway/Clare Regional Unit, and will determine grass growth.

Grazed grass is the cheapest feed and suckler beef producers must optimise the proportion of grazed grass in the total annual feed budget, he says and profitability is greatest where the calving date for suckler cows is aligned with the commencement of the grazing season.

“Where there is a long grazing season of 243 days, gross margin per hectare and profitability is highest. On any farm, grass supply and grazing season length is dependent on location, weather, stocking rate, and soil type, but most importantly on the fertility status of the soil on the farm.”

Fertility Status
Soil fertility is hugely influenced by soil pH (lime level), along with Phosphorous (P), Potassium (K) or Potash and Nitrogen (N) levels present in soil, he said. “The level and balance of NPK is hugely important. Both P and K are essential for plant growth, for the uptake and utilisation of Nitrogen by grass plants. Lime is the cement in the mix of NPK that makes them available to promote plant growth – ensure you have a correct level and balance of P, K and Lime on your farm.”

Fertiliser Plan
Taking soil samples and having a fertiliser plan drawn up by a Teagasc Adviser or agricultural consultant will achieve this while controlling fertiliser costs by pinpointing fields that have a deficit or surplus of P and K, he said “Any fertiliser plan should take into account all organic fertilisers (slurry, FYM etc) available to be spread after January 15, 2015.”

Soil Testing
Soil testing is the first step in fertiliser planning and now (November to January) is the ideal time to take soil samples, Anthony says. Ideally, samples should be taken by a professional agriculturist or someone trained to take soil samples.

For good soil test results ensure the following when soil sampling:
1. Soil sample every 2 to 4 ha (no individual sample should be more than 8ha);
2. Take soil samples to the correct soil sampling depth (10cm);
3. Take a minimum of 20 representative soil cores per sample;
4. Leave three to six months between sampling and the last application of P and K from either chemical or organic fertiliser;
5. Leave two years between sampling and any lime applications; and,
6. Include the farm’s herd number and LPIS parcel details for each individual sample when sending for analysis.

Lime Applications
Lime has a large influence on the plant-availability of both soil nutrients and applied organic or chemical fertilisers, as either nutrient, he says. Maintaining soil pH in the optimum range for either grassland (pH 6.3) or tillage crops (pH 6.5) will have a large effect on the availability of N, P & K.

For example grassland soils maintained at the target pH will release up to 80 KgN/ha/year and increase the availability of soil P and applied P compared with soils with low pH. Apply lime up to the target soil pH based on the lime requirement on the soil test report. Granulated limes, where used at low rates to replace ground limestone, should be applied every year to maintain soil pH.”

The optimum soil P and K index for grass production is Index 3, Anthony says, and building soil P and K levels will take a number of years depending on existing levels in fields. “Now is a good time to take out the fertiliser plan and identify fields that require additional P and K or Lime in the spring.”

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