Catch Crops for Water Quality
There are multiple benefits to using catch or cover crops in a tillage system. In terms of water quality it is the ability of catch crops to reduce nitrate (NO3-N) leaching that makes it a valuable tool for all tillage farmers.
Catch or cover crops in a tillage have a number of benefits for the tillage farmer these include:
- improved soil structure
- reduced compaction
- increased water infiltration
- reduced risk of soil loss in periods of heavy rainfall
Catch Crops to prevent Nitrate Loss?
Nitrate leaching is a process that happens naturally, it occurs when nitrate leaves the soil in drainage water. Nitrate is soluble and mobile particularly in free draining soils. Nitrate leaching occurs when nitrate is present in our soils during periods of low or no crop demand for growth. If soils are saturated or subjected to heavy rainfall, nitrate can leach down through soils and into groundwater. When the N is utilised by the plant there isn’t a problem but once it goes below the root zone of the plant and into the ground water it can find its way into the stream and river network. This can impact on water quality in the stream and river at high levels but can also have a big impact at the river estuary.
In a tillage system, the period post-harvest is the highest risk time for nitrate leaching. If soils are left fallow in the autumn/winter period with no growing crop in place, there is an increased risk that nitrate present will leach into ground waters. Simply put, catch crops will create a demand for nitrate in the soil and convert it into a growing crop rather than allow it be lost from the soil. The catch crop scavenges available nitrogen and other nutrients from the soil preventing this nitrate being leached into ground waters.
Catch crops can trap up to 60 – 120 kg N/Ha/yr that would otherwise be at risk of leaching into our groundwater.
Catch Crop Establishment
Sowing a catch crop in autumn or winter can reduce nitrate leaching losses, many cover species need to be sown before mid-August with sufficient moisture and good seed-to-soil contact been essential. The earlier the crop is established, the greater the potential to reduce nitrate leaching. The key to maximising nitrate capture is establishing a cover crop immediately after harvest. August-sown crops will provide more green material (dry matter) for grazing or incorporation, than September-sown crops. A variety of catch crops can be used to capture nutrients to build soil fertility and protect water resources.
There are a variety of targets to select from, mitigating nutrient loss and reducing soil erosion, including managing weeds and pests, environmental goals such as creating habitat building soil fertility and building soil structure.
Plan ahead to incorporate legumes or grasses as a catch crop at the end of the summer season. Select catch crop species mixtures carefully with regard to the functionality required and the impact they may have on crop rotation being practiced. It is essential to clear fields of straw as soon as possible after harvest so sowing can take place.
- Decide how catch crops fit into the arable rotation
- Selecting the right species and varieties will be dictated by the site and preceding crop.
- Consider the balance between cost effective establishment and appropriate seedbed conditions for the catch crops
- Be organised, purchase seed, have on site ready to go
- Establish as early as possible, clear any preceding crop and prepare the ground.
There are many advantages to using catch crop in any tillage system – both from soil health and environmental point of view and well worth the time and effort in planning their establishment. Successful catch crop establishment is one of the most important tools available to tillage farmers in helping to reduce the risk of nitrate leaching from their lands.
In this clip, Fiona Doolan, Teagasc ASSAP Advisor tells us more.
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