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Agronomy of catch cropping is an area in which we have plenty of room to improve


The estate comes with 150 acres laid out in tillage, pasture and woodland

The estate comes with 150 acres laid out in tillage, pasture and woodland

The estate comes with 150 acres laid out in tillage, pasture and woodland

For the majority of tillage farms, this is a more relaxed time of the year. However, it can be used as a time to rest, a good opportunity to collate records and compliance with the various regulatory regimes or to devise and implement a strategy for the coming year.

There are also a lot of crops in the ground, and while most are in excellent condition, regular monitoring is still necessary. Slugs, pigeons and crows are public enemies 1, 2 and 3 in this regard so ensure that they are not eating away at yield potential unbeknownst to you.

The recent autumn and winter period has allowed for excellent establishment of winter crops, which should enhance yield potential provided that they are managed correctly in the spring. One 'crop' however that requires careful management in excellent growing conditions are catch crops or cover crops.

This is an aspect of crop husbandry that is currently at a low level but is set to expand exponentially given the changes to the basic payment scheme. In fact, the agronomy of catch cropping is an area that we will all have to get good at, and soon.

The basic premise of cover crops is that they take up nitrogen that is made available over the autumn/winter period from the soil that otherwise would be lost and this nitrogen is then made available to the following commercial crop as the cover crop is broken down the following spring. However, sometimes it's not that simple.

The process of breaking down this cover crop, for the nitrogen to be made available to the following commercial crop, is a soil process carried out by soil micro-organisms. The activity or 'work rate' of these soil micro-organisms is determined by many factors, such as the amount of material they have to break down, soil temperature, soil moisture and general soil fertility levels. If any of these factors are not at an optimum, breakdown rates can be variable which has consequences for the following crop.

For example, if the amount of material to be broken down is very large, soil moisture levels or soil temperatures are low, or fertility levels are impaired (such as a low ph etc), the breakdown of the catch crop can be very slow.

While the process is ongoing, it is a net user of nutrients. What this means is that while the process of a cover crop being broken down is ongoing, it will soak up available nutrients from the soil, nutrients that should be available to the growing commercial crop. While all the nutrients will eventually be made available to the commercial crop, the timing of this availability is not according to the crop requirements. In fact, it is determined by natural soil processes, so it could happen late in the season.

In effect therefore, the catch crop could have a negative effect on the following commercial crop, not the desired positive effect. This could especially be a problem for crops like malting barley, where a flush of available nitrogen late in the season could have a negative effect on grain protein levels.

How do we minimise the risk of this happening?

Firstly, by not letting the cover crop develop too much, so that the bulk of material to be broken down is not too large. This is going to be a real risk this year. If a crop is developing too fast, the crop should be grazed or topped, or even rotovated in or sprayed off.

Secondly, there should be plenty of time given between incorporating the cover crop and establishing the subsequent commercial crop.

So the best approach is that as soon as spring growth commences, all cover crops should be chopped in or incorporated as the first job to do in the spring, and any crops destined for sowing in land where cover crops were grown should be the last sown, therefore the latest to establish.

The growing of cover crops has the potential to improve soil fertility levels which can provide a much needed improvement to tired worn tillage soils. They also have the potential to reduce the risk of nitrate loss to the environment.

However, growing catch crops is a complicated process and cropping must be well managed in order to minimise the risk of a negative effect to a cropping programme.

Dr Richard Hackett is an agronomist based in north Co Dublin and is a member of the ITCA and ACA.

Indo Farming