Nitrates leaching from tillage lands: What farmers should be aware of

Getting the balance right between fertiliser application and nitrogen utilisation is vital for farmers growing crops – both from an environmental and economic perspective, according to a new factsheet published by Teagasc.

The factsheet – titled “Nitrate Leaching from Tillage Lands” – is one of five published by Teagasc as part of the Agricultural Sustainability Support and Advisory Programme (ASSAP) this week.

Cereal crops have been traditionally sown on some of the better free draining soils in Ireland, the factsheet notes.

These crops have a capacity to take up chemical nitrogen (N) efficiently and convert it into significant yields of grain and straw nitrate to groundwater if the crop has not used all the applied fertiliser N by crop harvest time.

This surplus N is likely to be leached from the soil during periods of higher rainfall in autumn and winter.

The challenge in these fields is to ensure the tillage operations achieve maximum returns from applied fertiliser without having any negative impact on water quality.

Farmers can help reduce these losses by carefully managing fertiliser applications and targeted establishment of catch or cover crops, the ASSAP factsheet says.

Five key tips are advised to help reduce nitrate leaching from tillage fields:

Maximising Nutrient Use Efficiency (NUE) on your farm is the best way to minimise nitrogen losses to waters and also to improve crop profitability;
Ensure soil pH, Phosphorus and Potassium are at optimum levels. Soils at correct pH, P and K status will result in a higher nutrient uptake by the crop thereby reducing the risk of loss;
Nitrate leaching risk can be reduced by matching fertiliser application to the crop demand. Adjusting the timing and rate of application to match crop requirements, will ensure best return on money invested as well as reduced losses through leaching. There may be opportunities to reduce Nitrogen rates without impacting the yield of the crop;
Ensure soil temperatures are consistently at 6° or above before applying chemical Nitrogen. Low soil temperatures that do not support crop growth will increase risk of leaching to groundwater. Avoid application when rain is forecast within 48 hours or on wet or waterlogged soils;
To ensure efficient and accurate application of fertiliser, calibrate fertiliser spreaders and use GPS equipment where available.

Improved utilisation of chemical nitrogen by tillage crops will improve the financial return to the farmer but also reduce the risk to water quality.