Catch Crops
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A catch crop is any crop that is sown to utilise excess soil nitrogen that otherwise may be lost to the environment through leaching. Catch crops can also reduce sediment loss risk on your dairy farm. In addition to environmental benefits, catch crops can increase total annual dry matter production. This page highlights recent research in New Zealand that found cereals to be more effective than grass for this purpose after winter grazing.
What is a catch crop?
A catch crop is any short-term crop that is grown with the primary objective of using excess nitrogen and other nutrients in soils that otherwise may be lost through leaching or overland flow. After summer and winter grazed crops (such as summer turnips, winter brassica or fodder beet) there is residual nitrogen in the soil, caused predominantly by urine patches from cows grazing at high densities. The catch crop's uptake of this nitrogen and reduction of the soil water content reduces the risk of drainage and nitrate leaching.
The key qualities of catch crops when following summer or winter grazed crops are that they germinate and establish well and can actively grow in cooler soil temperatures, are cold tolerant and have fibrous deep root systems capable of removing nitrogen at depth.
Why should I use a catch crop?
Bare ground left after grazing of fodder crops is a risk for overland flow of nutrients and soil from the paddocks and leaching of nitrogen. Catch crop benefits vary depending on weather conditions, particularly during establishment, with direct-drilling or light pre-drilling cultivation being recommended methods where possible to reduce nitrogen mineralisation.
As well as using a catch crop, other practices you can consider for reducing sediment and nutrient loss risk on your dairy farm over winter are:
- Re-establish new pasture as soon as practical after crop grazing to reduce overland flow risk and increase nutrient uptake.
- Maintain grass buffers between the paddock and critical sources areas to ensure sediment is not lost from the paddock.
- Have a plan in place for prolonged wet weather conditions, to reduce the risk of pugging and soil damage to paddocks.
When should I use a catch crop?
Research trials have shown that using a catch crop can significantly reduce nitrate leaching. The main factors influencing the ability of a catch crop to reduce nitrate leaching potential are early crop establishment, autumn/winter rainfall, establishment method and if required, how and when nitrogen fertiliser is applied.
The earlier the crop is planted, the greater the opportunity to reduce nitrate leaching. The Agriculture Production Systems sIMulator (APSIM) was used to model nitrate leaching loss from a forage oat catch crop following grazed fodder beet under normal rainfall and a low water-holding capacity soil. Different planting dates were compared with fallow, resulting in the percentage reduction compared with fallow, shown in the table below.
Variation caused by rainfall, methods of sowing (i.e. direct drill vs cultivation) and potential fertiliser use in later stages of crop growth are not shown in this table. These will also influence catch crop performance.
For more information on forages to reduce nitrate leaching research results see the management guidelines.
Nitrate loss reductions (%) compared with fallow, modelled with APSIM
| Sowing date | Southland | Canterbury | Hawkes Bay | Waikato |
| June | 22% | 41% | 20% | 34% |
| July | 17% | 33% | 7% | 27% |
| August | 8% | 26% | 4% | 19% |
| September | 0% | 14% | 2% | 6% |
Adapted from 'Catch Crops for Reduced Nitrate Leaching', 2021.
Sowing catch crops
To maximise the yield of catch crops and reduction in nitrate leaching, it is recommended to target high plant populations (e.g., 300 plants/m2 for cereals). This will minimise the time it takes for crops to reach canopy closure and maximise growth and nutrient uptake.
Aim to sow cereal catch crops at about 30-40 mm depth or grass catch crops at 10-20 mm. This will ensure good soil-to-seed contact and reduce the risk of birds eating the newly sown seed.
Broadcasting of seed increases the risk of uneven establishment and crop failure. Fertilisers will not be required, especially early in the growth phase.
Types of catch crops
A variety of species or combinations can be used as catch crops.
When selecting species consider the following:
- Establishment opportunities of the catch crop, the usual soil temperature at the time of planting, and whether heavy machinery can normally access the paddock at that time of year.
- Main crop/regrassing planting date; effect on potential yield of the following crop or pasture.
- Ability to fit into the farm system, e.g. planned crop rotation, harvesting or grazing dates, end use of land planted (permanent pasture or crop).
- Intended use of the catch crop, for example, green manure, grazing, green chop / whole crop silage, grain or straw.
Some examples of catch crops are:
Oats: A fast-growing cereal that germinates well in low soil temperatures and can be sown in autumn, winter and spring. Used for winter green feed, green manure or silage.
Triticale: Tall cereal developed from crossing wheat and ryecorn. Some varieties can be planted in autumn and winter behind grazed crops.
Ryecorn: Used in dryland situations where it is sown in early summer for grazing through until spring.
Italian ryegrass: Establishes quickly and will grow at lower temperatures than perennial ryegrass. It can be sown by itself or in combination with a cereal crop. The mixed crop can be harvested for silage, after which the grass provides the opportunity for multiple harvests and under-sowing of permanent pasture later without needing further cultivation.
Faba beans: Best planted between early March to late April following a summer crop to use as a late spring feed. This legume fixes nitrogen, which in some crop rotations can be beneficial for the next crop.
Talk to your agronomist to match the best species and cultivars to your farm system and goals.
Different crops effectiveness in nitrogen uptake
Research trials conducted in Waikato, Canterbury and Southland compared different catch crops for their plant nitrogen uptake and amount of mineral nitrogen remaining in the soil, to reduce the risk of nitrogen leaching. The trials also compared the different catch crops for their biomass production at various stages.
The research found that:
- While all catch crops can reduce nitrate leaching and produce significant dry matter yield, some performed better than others.
- Cereals (e.g., oats, ryecorn, triticale, wheat or barley) are more effective than grass species (e.g. Italian ryegrass) as catch crops after a winter grazed crop.
- The earlier the catch crop is planted, the greater the opportunity to reduce nitrate leaching.
- Catch crops can increase total annual yield of a paddock.
For more information on forages to reduce nitrate leaching research results see the management guidelines.
Calculating and comparing costs of different catch crops
The gross margins (revenue minus costs) and cents per kg dry matter of different catch crops can be compared to select the best fit.
The numbers will vary depending on the yield of the catch crop and how it fits into an individual farm system. This is influenced by catch crop sowing date, the timing of feed requirements, and the sowing date of the following crop or pasture. Speak to your local agronomist for advice.
To compare gross margins and cost of different catch crops, use the catch crop gross margin calculator.
Key takeaways
- Planting catch crops earlier increases their effectiveness in reducing nitrate leaching and sediment loss and can boost the annual yield of a paddock.
- Other recommendations to reduce sediment and nutrient loss risk include maintaining grass buffers, resowing new pasture as soon as practical, and reducing the risk of soil damage caused by pugging.
- Cereals (e.g. oats, ryecorn, triticale, wheat or barley) are more effective than grass species (e.g. Italian ryegrass) as catch crops following a winter crop grazing.
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