Explained by Teagasc: National soil fertility trends 2021

Figure 1: Signpost Climate Actions for November

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. Farmers should take heed of this early warning in order to put plans in place to protect the productivity and long-term sustainability of their farming business going forward.

During the period 2015 to 2019, good progress was made across all farming enterprises in relation to soil fertility improvements. In the last 2 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.

National Highlights

• All farm enterprises took more soil samples in 2021
• Overall decline in soils with optimum soil fertility to 16% (-3%)
• Soil pH declined to 54% of soils with a >pH 6.2 (-8%)
• Soil P levels at Index 1 & 2 increased (54%) while soils at Index 3 & 4 decreased (46%)
• Soil K levels remain similar with a slight decrease in soils at K index 4

Enterprise Highlights 

Dairy

• 16% of soils have optimum pH, P & K (3% decrease)
• 53% of soils with a soil pH >6.2 (10% decrease)
• 55%of soils at P index 1 & 2 (4% increase)
• 48% of soils at K Index 1 & 2 (no change)

Drystock

• 13% of soils have optimum pH, P & K (2% decrease)
• 47% of soils with a soil pH >6.2 (10% decrease)
• 61%of soils at P index 1 & 2 (11% increase)
• 50% of soils at K Index 1 & 2 (3% increase)

Tillage

• 18% of soils have optimum pH, P & K (6% decrease)
• 61% of soils with a soil pH >6.5 (13% decrease)
• 57%of soils at P index 1 & 2 (7% increase)
• 32% of soils at K Index 1 & 2 (2% decrease)

Key Messages from the Results

1. 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.

2. Close attention is now required to manage soil fertility

Over the last 2 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 required to prevent a reverse of fertility improvements achieved in previous years. 

3. 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 required most, and thirdly select a suitable P and K fertiliser blend to maintain farm soil fertility.

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