Catch crops important following dry season to take up leftover nitrogen
Cover crops, catch crops, forage crops – it’s the time of year for them.
On this week’s Teagasc Tillage Edge Podcast, Richie Hackett gave a run down of the differences, the advantages and the environmental benefits of these crops.
Speaking about the different terminology he stated that a cover crop is used to protect the soil from erosion and is “a crop that’s grown during the fallow period between two cash crops and is grown to give some benefit to the succeeding crop without necessarily being harvested as a crop in its own right”.
A catch crop is used to catch nutrients and prevent them from being lost, such as nitrogen (N), and a green manure is something that’s used to provide a benefit to the next crop in terms of nutrition.
Richie noted that terms are used interchangeably and often mean the same thing.
However, he would make a distinction between a situation where a crop is grown to protect or enhance the soil – a cover crop – and a forage crop where the main aim is to grow a crop to feed animals later in the season.
Forage crops often have fertiliser applied to increase growth and provide more fodder for the winter period. Richie did add that some farmers will graze off cover crops as a method of destruction.
Sowing time is very important.
“The benefits of a cover crop will depend on how much organic matter or growth is being produced – how much material is being returned back into the soil.”
It’s important to try and sow cover crops as early as possible to increase the amount of biomass that it produces.
Prevent nitrate leaching
Aside from providing a cover, Richie explained that one of the main benefits of growing catch crops is to prevent nitrate leaching during the autumn and winter period.
“Nitrate is a very leaky nutrient and any nitrate that’s in the soil over the winter period – under our conditions – will be washed out of the soil and into water bodies; we only have to think about what happened over the last autumn/winter period in terms of rainfall.”
When nitrate enters a water body, it can cause pollution and decrease water quality. Farmers are obliged to prevent N loss under the nitrates regulations.
“In order to avoid tighter regulations in the future, it’s important that we minimise losses of nitrate as much as possible and cover crops are a very effective means of doing this – particularly in arable situations in advance of a spring crop.
Any nitrate that has been taken up by a cover crop over the winter period can’t be lost and it’s potentially there for the succeeding crop.
Dry weather and poor-yielding crops may mean a lot of the N applied to crops is still in the ground.
“It’s very important to remember that we’ve had a very bad drought. Yields so far are disappointing and spring crops look quite poor in many areas.
“It’s likely they will not have used much of the N that was applied to them, so there may even be more N lying in soils compared to other years.
It’s quite important that we try and prevent as much of that [N] as possible from getting into our rivers.
Catch crops can also prevent phosphorus (P) loss as the cover on the ground can help to prevent overland flow, as opposed to N which leaks through the soil, and to help to hold soil together.
Richie explained that loss of P through overland flow and through soil particle loss are the main methods of P loss.