Water Quality and Nutrient Management
Noel Meehan, Teagasc Programme Manager - ASSAP, writes about water quality and nutrient management, and gives advice for farmers to minimise nitrate losses.
Nitrate loss from farming impacts primarily ground water and estuarine/coastal waters. A drinking water limit of 50 mg/l NO3 is set for groundwater. Very few groundwater sources breach this limit. However concentrations are increasing in groundwater in the south and south east of Ireland.
Estuarine/coastal waters along the south and south east of Ireland are impacted with the majority not reaching WFDs ‘good status’ target. Nitrogen generally does not impact surface waters to the same degree as Phosphorus. EPA published a Nitrogen Catchments of Concern report in 2021. It highlighted 12 river catchments that are impacted by excess nitrate losses.
Losses from grassland sources are the largest contributor to nitrate losses across all 12 catchments. However nitrate arable losses in the Slaney and the Barrow catchments account for approx. 30% of the load.
Use of EPA PIP N maps will help farmers to establish if there land is N risky.
Stubbles or soils with no growing root or cover are prone to nitrate loss during the winter on free draining soils.
Sean Doorley, Teagasc Advisor caught up with Padraig Fitzgerald, ASSAP Advisor, Teagasc at #Ploughing2022 to discuss cover crops and water quality. Cover crops are used by tillage farmers after crops are taken up to avoid nutrient losses to ground water. Cover crops will help maintain water quality in Ireland.
Advice for farmers to minimise nitrate losses
For grassland
- Need to improve nitrogen use efficiency (NUE)
- Get P, K and pH correct to maximise grass growth
- Apply fertiliser in accordance with a NMP
- Apply fertiliser at the Right time: Soil temperatures + soil moisture deficits (saturation & drought) + rainfall forecast + growth rates
- Apply fertiliser in the Right location: drier fields in spring, best fertility, best swards, avoid critical source areas
- Apply fertiliser at the Right rate: match application rate to crop demand and growth rates
- Apply fertiliser at the Right product: protected urea aids in reducing nitrate leaching. LESS and clover can also help but clover is a nitrogen source and can result in nitrate losses
For tillage
- Improve NUE – same as above
- Minimise nitrate losses post-harvest by incorporating a cover/catch crop
- Cover crops reduce leaching, overland flow and soil erosion due to having a growing crop in over the winter, however the crop must be established as quickly as possible after harvest in order to ensure good establishment. Growth rates drop rapidly in September due to reduced daylight and reduced temperatures. The rooting of the cover crop breaks up compaction (especially brassicas), however farmers should not continually sow brassica cover crops as club root can become an issue (important to rotate crops)
- Cover crops create a source of additional organic matter back to soil, food for microbes and even improves the diversity and abundance of microbes in the soil