Catch Crops

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.

Nitrate loss reductions (%) compared with fallow, modelled with APSIM

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.

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.