Cover crops lauded by practicing growers

Winter cover, or green cover, is one of the options that tillage farmers have in the future to provide ecological focus areas (EFA) for greening. The cover option will also be used by some growers to fulfil the crop diversification or three-crop rule within GLAS, where insufficient crops are grown.

But, for some tillage farmers, green cover crops are just a part of good farming practice.

At the recent Irish Tillage and Land Use Society (ITLUS) conference, Richie Hackett from Teagasc provided the background to catch crops and outlined some of the main findings of recent research.

Autumn-planted green foliage crops are known by many names and Richie said that the appropriate name is most often associated with the reason for planting.

Catch crops are named because their purpose is to ‘‘catch’’ nutrients and prevent leaching over winter. And it is well accepted that they do this.

But the level of success depends to some degree on how early they are planted because early drilling means more autumn growth and more nutrient uptake.

The main uncertainty is when these nutrients will be re-released in springtime to support growth.

The purpose of a cover crop is to cover the soil over winter to help protect it from being degraded by rain. To do its job, it needs to cover the soil surface but it must remain in place until the risk of heavy rain has passed so it must be in place for longer. The foliage is then burned off or grazed before spring cultivation.

Green manures are grown to improve the soil and enhance yield in succeeding crops. They are primarily about generating and trapping nutrients to have them re-released in the following crop to promote growth.

Soil benefits

While the specific names signify a focused intent, all of these autumn crops fulfil these same requirements to a greater or lesser extent.

They all trap vulnerable nutrients, protect the soil for as long as the foliage is in place and help to recycle nutrients to the following crops.

And they all help soil by providing organic matter to promote earthworms and other biological activity.

Richie listed a series of benefits from any or all of the crop types. These include:

“One can argue for potential disadvantages also,” Richie said. Depending on the species planted and the method of planting, these crops can:

Richie outlined the different crop groups that can be used to fulfil these roles. They can range from grass to legumes and brassicas take in a big chunk of the practical choice on farms. Westerwold ryegrass is often used for fodder but it also mops up autumn nutrients.

All of these autumn crops provide these benefits to a lesser or greater degree. They all provide one other common benefit – improved soil through increased biological activity and soil structure.

Richie said that the overall effect on soil organic matter level is small, as the roughly 3t/ha DM input per annum will only equate to approximately a 0.01% to 0.02% net increase in soil organic matter.

This modest level of soil organic matter increase can still affect soil water and temperature, and these benefit growth.

But incorporated organic matter will have a big effect on the level of active organic matter degradation and this generates the biological activity that drives up potential yield over time.

The benefits from these crops will be influenced by the volume of biomass generated. The biggest consequence is seen through increased earthworm activity. And this is paralleled over time by increased water percolation through the soil.

Many of the ponds that have appeared in fields over the past decade or two are a result of soil tightening and decreased percolation. Deteriorating soil structure causes soil pores to become clogged up where structure is not repaired by biological activity.

Soils that are being restructured have higher soil aggregate stability and this makes them more resistant to the damaging effects of rainfall.

Effect on yields

Catch crops have the potential to affect crop yields. However, the results shown in trials from around the world tend to be somewhat neutral in this regard.

Richie showed us that some yield responses were positive while others were negative. This response is likely to be influenced by the weather in springtime.

The volume of growth or biomass produced in the autumn is heavily influenced by time of sowing and nutrient availability, especially nitrogen.

Richie’s Irish results showed definite benefits in terms of nitrate loss. However, uptake of nutrients by a cover crop did not equate to a reduced requirement for the following crop.

Yield results from catch crops on a light Oak Park soil between 2004 to 2006 were largely positive, but not all significantly beneficial. On a medium soil, the yield responses tended to be negative but not significantly so. Richie will present more of these findings at the Tillage Conference in January.

However, it is likely that many trials examined once-off yield responses following a catch crop.

It seems likely that ‘‘once-off responses’’ will be evened out over time where catch crops are sown on a frequent basis.

Farmer practices

Two young growers with an eye on the future outlined their experiences of using green manures in recent years. They both agree that they are seeing benefits in terms of both soil structure and soil behaviour. The main benefits recorded were reduced ponding in fields and improved moisture retention in lighter spoils.

Philip Reck manages a big farming business for Walter Furlong in Wexford. This is mainly a spring barley operation with some winter barley and there will also be some beans next year to comply with the three-crop rule.

On this farm, EFA will be provided by a combination of hedges, drains and buffer strips, combined with cover crops ahead of spring crops.

Catch crops have been part of farming practice for the past five years. They grow them to help improve soil structure and alter management and establishment processes. All land destined for spring crops is now sown with a catch crop mix in the autumn, as soon as possible after straw is removed.

Philip uses a 12m Vaderstad Carrier fitted with a Bio-Drill seeding unit, so that a single pass both cultivates and plants the seeds. This involves a light cultivation using discs, broadcasting the seeds and then a packer roller. The combination enables moisture conservation and timely establishment.

Radish, specifically tillage radish, forms the basis of the catch crop mix that Philip uses, along with a winter pea and vetches.

The radish produces a long tap root, which provides a nutrient reservoir between crops, which grows deep into the soil to provide channels for water percolation and roots.

The legumes in this mix produce nitrogen to help feed the growth and the biomass then feeds the soil biological complex, which restructures the soil and makes it easier to work over time.

Philip stated that the use of catch crops has already brought many visible benefits. These include improved soil structure, more active soil biology, improved water percolation and drainage, better water holding capacity in lighter areas and decreased requirement for diesel, steel and chemistry. All of these observations are helped by increased earthworm numbers.

Philip Reck

Since the ITLUS conference, I visited some of Philip’s crops where the three-species combination grew to nearly hip height in the autumn. Now, the peas have largely died and are beginning to rot back into the soil.

The pictures (left) show the volume of growth the catch crop produced (unfertilized) and the fact that the peas and vetch are now dying back. For as long as the radish continues to grow it will capture more nutrients, penetrate deeper into the soil and continue to generate biomass for the soil’s biological system.

The peas that are now rotting back into the soil are helping earthworm activity, which can also be seen in the reduced amount of stubble remaining on the soil surface.

Philip will burn off any remaining vegetation in springtime and then plant the next crop using shallow min-till cultivation. The need for deeper tillage is replaced by the open nature of the soil beneath and this is a direct saving on metal and diesel.

Jonny Greene

Jonny Green, from Athy, said that, in his opinion, the greening components in the new CAP are more positive than negative. He is one of an increasing number of farmers who recognise that yields are going backwards, with soils disimproving over time. “This is even more apparent on lighter soils,” Jonny said.

“We will not have to change anything to comply with greening on our farm,” he said, “as we have already adopted practices to improve our soils. These make us compliant for crop diversification and EFA.”

Jonny explained that moisture is often a limiting factor on his light shallow soils. Fields have been showing signs of tiredness from mono-cropping and yields have plateaued, if not declined.

To help address these problems Jonny moved to min-till systems and then to strip-till/direct drilling. This has helped give most of the soil a rest from aggressive tillage.

Organic manures were also brought in and Jonny began to practise rotational incorporation of crops residues. Cover crops were introduced and livestock numbers have been increased on the farm.

More non-cereals and fertility building crops, like legumes, were introdued to the rotation. And a move to yield mapping and soil mapping helped to monitor soil/field variability, which decreases as soil health improves.

“The benefits can already be seen. Weak patches have all but disappeared from fields and we see far fewer ponds following heavy rain. Headlands now look like the field and P and K indices have risen. We think we are seeing improved moisture retention but we spend fewer hours on tractors cultivating,” Jonny said.

He said he will do more cover cropping, both in winter and summer, and chop any straw that is not needed on the farm. The objective is to have less soil disturbance to enable roots and worms to do their work.

Experiences to date have been variable with catch crops. But soil conditions did improve quickly and now better advice is needed on the choice of species to use ahead of different crops.

Jonny has previously grown catch crops such as oats, Westerwold and Phacelia but he is now using a mixture comprising sunflowers, Phacelia, buckwheat, oilseed radish and vetch.

As well as being a cover crop, Jonny also uses this mix as a feed for ‘‘bed and breakfast’’ sheep, which brings yet another benefit to the farming system.

“Spring crops only use the ground from March to August (five months) so there must be opportunities to do other things with land,” he said.

Jonny urged all tillage farmers to give the soil more thought. Things like rotation, organic matter incorporation and catch cropping can bring definite advantages to the soil and bank balance.

All farmers recognise the increasing cost base and the yield plateau but it is up to each individual to find his/her best solution. “We need to bring farmers back in touch with what gives us our livelihood – the soil,” Jonny said.