Catch crops

The purpose of a catch crop is to increase annual dry matter production, to take up soil mineral and urine nitrogen and to reduce the risk of leaching or runoff.

The key attributes of catch crops when following autumn or winter grazed crops are that they:

are cold tolerant
are winter active
have fibrous deep root systems capable of removing nitrogen at depth.

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 minimise nitrogen mineralisation.

Catch crop costs

The gross margins (revenue minus costs) and cents per kg dry matter of catch crops can be used to compare different crops.

The numbers will vary depending on the yield and how the crop fits into an individual farm system, which is influenced by catch crop sowing date, the timing of feed requirements and the sowing date of the following crop or pasture.

The Forages for Reduced Nitrate Leaching (FRNL) research trials gross margin and c/kg DM varied from $173/ha to $1263/ha and 8.1 c/kg DM to 15.3 c/kg DM respectively. For more examples see the management guidelines below.

To compare gross margins and cost of different catch crops, use this spreadsheet.

Species to consider

FRNL ran trials of different crops comparing crop nitrogen uptake and residual soil nitrogen as indicators of the risk of nitrate leaching.

A variety of species or combinations can be used as catch crops. Consider the below when selecting species or combinations thereof:

Establishment opportunities of the catch crop; what is the usual soil temperature at the time of planting and can heavy machinery normally access the paddock at that time of year?
Main crop/regrassing planting date; consider 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), use of catch crop:
- green manure
- grazing
- green chop / whole crop silage
- grain or straw

Examples of catch crops

Oats: A low temperature germinating, fast-growing cereal that can be sown in autumn, winter and spring. Used for winter green feed, green manure or silage. For more information click here.

Triticale: Tall cereals developed from crossing wheat and ryecorn, some varieties can be planted in autumn and winter behind grazed crops. For more information click here.

Ryecorn: Used in dryland situations where it is sown in early summer for grazing through until spring. For more information click here.

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. For more information click here.

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. For more information click here.

Optimising catch crops

To maximise catch crop yield and reduction in nitrate leaching it is recommended to:

target high populations (300 plants/m²) with cereals, to minimise the time it takes for crops to reach canopy closure
aim to sow seed at about 3 cm depth, to ensure good soil-to-seed contact, and reduce the risk of bird damage
add phosphorus (50-100 kg P/ha as Triple Super) down the spout with the seed to aid the establishment of oats. Nitrogen will not be required early on in the growth phase, so avoid using DAP. Typically after a grazed crop, nitrogen fertiliser will not be needed at all for a catch crop.

How catch crops help the environment

A catch crop is any crop that is grown with the primary objective of catching excess nitrogen in soils that otherwise may be lost through leaching. The reduction in nitrate leaching losses results from the crop's rapid uptake of residual mineral nitrogen and the reduction of the soil water content of the soil, which reduces the risk of drainage.

Sowing a catch crop in autumn or winter can reduce nitrate leaching losses. The earlier the crop establishment, the greater the potential to reduce nitrate leaching.

DairyNZ's FRNL project ran catch crop trials in Waikato, Canterbury and Southland comparing different species for biomass at green chop (beginning of November), whole crop silage stage (end of December 2018) and plant nitrogen uptake.

The results showed that while all catch crops can reduce nitrate leaching and produce significant yield, some performed better than others. Cereals (e.g. oats, ryecorn, triticale, wheat or barley) can be used as catch crops after winter grazing and are considered more effective than grass species (e.g. Italian ryegrass). It is recommended that an agronomist is consulted to match the best species and cultivars to your farm and goals.

Reducing nitrate leaching

FRNL research trials have shown that using a catch crop can reduce nitrate leaching. The main factors to reducing nitrate leaching potential are early crop establishment, autumn/winter rainfall, establishment method and how and when nitrogen fertiliser is applied.

The earlier the crop is planted, the greater the opportunity to reduce nitrate leaching. The following table shows the modelled nitrate loss reductions (%) at different planting dates of an oat catch crop following grazed fodder beet.

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%

The variation in rainfall, methods of sowing (i.e. direct drill vs cultivation) and fertiliser use are not shown in this table. These will also influence catch crop performance. For more information on these research results see the management guidelines at the end of this page.

FRNL farmers' experience with catch crops

As part of the FRNL programme, three Canterbury dairy farms established catch crops of oats or oats/Italian ryegrass mix. The first crops were planted in late autumn/early winter 2017 (30 May – 20 June) following grazed fodder beet.

The 2017 season was relatively wet when these crops were first planted. Despite this, all three catch crops successfully established and took up nitrogen (N) from the soil.

Final yields at each of the sites ranged between 1.8 and 9.7tDM/ha, with up to 89kgN/ha accounted for in above-ground biomass.

The low yielding crop at the Mayfield site was largely due to the crop being sprayed early and incorporated as green manure, as opposed to the other two crops that were grown and harvested for green-chop silage in November/December. However, as the Mayfield site was the earliest to get the crop into the ground (30 May), they observed a noticeable effect on N uptake.

Mayfield Farm

Grant and Jan Early trialled using catch crops after autumn grazed fodder beet in an attempt to harvest excess N from the soil and reduce their N leaching footprint, while maintaining or improving profitability.

In 2017, the couple planted a crop of oats on 30 May, immediately following grazed fodder beet. The paddocks were cultivated with two passes of a Sumo cultivator and a Cambridge roll, and then planted with a conventional seed drill, sowing the oats at 120kg/ha.

This crop was taken through to September when it was sprayed and incorporated back into the ground as green manure. Due to the shorter growing period, the yield of the crop was low at 1.7tDM/ha. However, as they were able to plant the crop so early, this had a positive effect on the N uptake, with 53kgN/ha taken up by the plants over that period.

In 2018, Mayfield again trialled catch cropping, this time using Barley as their crop of choice over three different paddocks. Planting dates ranged from 14 July to 29 August, allowing a good comparison between early and late planted crops in their ability to take up N from the soil, compared with leaving the land fallow. All crops were planted at 130kg/ha.

Sowing date had a noticeable effect on yield (7.3-11.9kgDM/ha) and N uptake (174-195kgN/ha), with higher yields and N uptake observed in the earlier sowing date treatments. This highlights the importance of sowing catch crops as early as possible.

Metabolisable energy of the crops was also measured at harvest and ranged from 11.9-12.3MJME/kgDM for whole crop silage, and averaged 14.4MJME/kgDM for the barley grain.

More results

For more results of catch crops on FRNL monitor farms, click here.

For results of a survey amongst farmers about their use of catch crops, click here.