Farming & Fisheries

TEAGASC: Trends indicate early signs of a decline in soil fertility

October 7th, 2022 7:05 AM

By Southern Star Team

Close attention is now required to manage soil fertility. (Photo: Shutterstock)

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THE 2021 soil fertility results indicate that soils with optimum pH, phosphorus (p) and potassium (k) fertility decreased by 3% to 16%.

These trends could indicate early signs of declining soil fertility levels nationally.

Unfortunately, these downward trends, coupled with reduced fertiliser (P & K) use in 2022 will likely lead to further running-down of soil nutrient reserves, which will impact negatively nitrogen use efficiency and crop yields in the coming years.

During the period 2015 to 2019, good progress was made across all farming enterprises in relation to soil fertility improvements. In the last two years, both dairy and drystock farms are showing a combined 5% drop in soil fertility.

On tillage farms, a similar trend is emerging in 2021 with a 6% decrease in soil fertility.

Nationally, all farm enterprises took more soil samples in 2021 but there is an overall decline in soils with optimum soil fertility.

Soil pH >pH 6.2 declined and soil p levels at Index 1 and 2 increased while soils at Index 3 and 4 decreased. Also soil k levels remain simialr with a slight decrease in soils at k index 4.

Drystock: 13% of soils have optimum pH, p and k (2 % decrease) while 47% of soils have a soil pH >6.2 (10% decrease). Also, 61%of soils at p index 1 and 2 (11% Increase) and 50% of soils at k index 1 and 2 (a 3% Increase),

Dairy: 16% of soils have optimum pH, p and k (3 % decrease) while 53% of soils with a soil pH >6.2 (10% decrease). Also, 55%of soils at p index 1 and 2 (4% Increase) and 48% of soils at k index 1 and 2 (no change).

Tillage: 18% of soils have optimum pH, p and k (6 % decrease) and 61% of soils have a soil pH >6.5 (13% decrease). Also, 57%of soils at p index 1 and 2 (7% increase) while 32% of soils at k index 1 and 2 (a 2% decrease).

Therefore, there is a large requirement to apply lime. Results in 2021 now show that 47% of dairy farms had soil pH below the optimum of pH 6.3. In the other enterprises, soil pH was below optimum in 53% and 39% of soil samples taken on drystock and tillage farms, respectively. This shows that there is still a large requirement for lime on Irish farms despite record levels of lime applied in 2021.

Also, close attention is now required to manage soil fertility. Over the last two years, the number of soil samples from grassland with optimum p (greater than index 3) have shown a decrease, while soil k levels have remained stable over the same period.

On tillage farms, a similar trend is emerging in 2021, with a drop in soil p levels and an improvement in soil k levels. Action is needed now to prevent a reverse of fertility improvements achieved in previous years. Finally, an up-to-date nutrient management plan is important.

With artificial fertiliser costing almost three times as much as two years ago, preparing and implementing a nutrient management plan has never been more important.

Plans should be based on up-to-date soil samples, should focus firstly on correcting pH, secondly on getting the most from slurry and manures by identifying where it is needed most, and thirdly selecting a suitable p and k fertiliser blend to maintain farm soil fertility.

Pauline O’Driscoll is a B&T dairy advisor based in the Skibbereen office.

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