Arable News

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Shallow cultivations and cover crops deliver results

Agrovista’s heavy land trials site in Northamptonshire, Project Lamport, continues to focus on finding solutions for growers to reduce black-grass on their farms. This year, trials have also highlighted soil health and cultivation benefits. Dominic Kilburn writes.

While there’s no doubt that a lot of UK arable farmers are focusing their attentions on reduced cultivations and moving towards direct drilling regimes, for agronomic and cost saving reasons, many farmers still operate under the principle of “the sooner we get the cultivator in behind the combine, the better”.

That’s according to Agrovista technical consultant Niall Atkinson who is involved with the company’s heavy land black-grass site, Project Lamport, near Maidwell in Northamptonshire.

In recent trials work there, the combination of shallower cultivation tines and cover crops over two very different seasons has delivered good results in terms of setting up land in the autumn for a crop to be drilled the following spring.

Mr Atkinson reckons that pulling a tine through the ground at 200–250mm after harvest is still accepted as normal practice on many farms, and sometimes without a true understanding of why it’s being done. “Pulling tines through at that depth not only mixes black-grass seed down through the soil profile, resulting in germination from variable depths, but it can also do quite a lot of damage to the soil structure itself,” he pointed out.

“Let’s imagine we achieved an average yield of between 10–12t/ha of wheat across a field, then the soil will have been pretty well structured to deliver that. So why do we go in and destroy the root and worm channels getting rid of the natural re-structuring that has occurred?

“I know from my past experience as a farms manager that it was easier for me to say ‘cultivate everything’, and a lot harder for me to say ‘don’t cultivate’, but proper soil diagnostics can help us decide when we need to cultivate and where,” he added.

Black-grass focus

Primarily, Project Lamport was started seven years ago to help growers on heavy land with the ever-increasing burden of black-grass, and Mr Atkinson said that this remains the number one priority for the trials site.

The two “big hitters” for successful control over that time have been spring crops and rotational ploughing, with other cultural control methods collectively assisting to help achieve the desired level of control.

“That said, heavy and wet soils don’t lend themselves to spring cropping and this is where we have seen the benefit from cover crops in the past few years of the trials,” explained Mr Atkinson.

He said that it is key that cover crops (or more accurately in this case described as catch crops) don’t smother the black-grass – better that they allow the black-grass to germinate at the same time.

“A seed rate of about 75 plants/m2 for the catch crop is about right because we want to encourage the activity from the black-grass,” he explained.

According to Mr Atkinson, catch crops including black oat, berseem clover and phacelia have been most successful at Lamport – black oat has been particularly good at getting its root system down and creating drainage, helping to move water down through the soil profile.

“When it comes to direct drilling of the spring crop, we want as little soil disturbance as possible and as well as its good drainage-creating properties, black oat roots stabilise and hold the soil together when going through with a drill,” he pointed out.

“What we have observed with fallow plots however, where no catch crops were planted, is that there is more water run-off during the winter months. And so when it comes to direct drilling in the spring, the soil is very wet underneath the surface as it has had no conditioning. Along with that, one typically sees an increase in black-grass and poorer crop yield by comparison,” he said.

Soil health

As well as success in reducing black-grass levels and growing spring cereals on heavy land, Mr Atkinson said that over time the trials have also shown clear soil health benefits, and this prompted Agrovista to look at the interaction of roots with and without cultivator metal passing through the soil.

Over the past 2 years, autumn trials have included up to 11 different treatments with tines passing through the soil at 125 and 250mm depths, with and without planting catch crops (black oats and phacelia), as well as plots left untouched (fallow).

In the following spring, wheat was direct drilled over half the width of each plot with the crop monitored for the remainder of each season.

“Autumn 2017 turned out to be a very wet one,” continued Mr Atkinson. “In a wet year we know we’ve been doing it wrong with deeper (250mm) cultivation because the soil is like plasticine and the tine creates smearing at depth. However this is still something routinely carried out by growers in the autumn.

One of the take-home messages from Project Lamport this summer was that the more roots there are in the soil, and less disturbance via cultivation, the better.

“Where we went shallow in those conditions, we have effectively lifted the soil very slightly which has really helped the catch crops get their roots down.”

This was repeated in 2018 – an exceptionally dry autumn by contrast – and there appeared little difference between 125mm- and 250mm-cultivated plots where a catch crop had been established. However when soil loosening took place and no catch crop established, leaving the land bare over winter, slumping occurred. “When catch crops are introduced, the roots and wetting help soils naturally restructure,” he explained.

“Shallow cultivation with catch crop roots generally gave the best results in terms of black-grass control, soil structure and, ultimately, yield.

“While the deeper we went the more we seemed to be spreading the black-grass through the soil profile.

“I am not advocating that a 125mm cultivating depth and catch crops are right for every situation – each field has a different requirement – although we have seen consistent results from cultivating shallower over two very contrasting seasons to set up the crop for the following spring. But the default position of pulling a tine through the soil as deep as the tractor can manage is probably the wrong thing to do most seasons,” said Mr Atkinson.

“I think the thing growers find hardest is justifying the cost of a cover or catch crop, however you’ve only got to look at the fuel savings of going shallower to realise the potential there is to save costs.

“We must understand what’s happening below ground – and there is an opportunity to save money while also improving the soil’s health,” he pointed out.

For this autumn, trials are continuing with a closer look at the effects of tyre compaction at both 9 and 18psi pressures.

Field fuel consumption will also be measured and compared between different cultivation depths.

“Most importantly we will be questioning whether there is a need to cultivate in the first place,” concluded Mr Atkinson. “A lot of machinery is getting bigger and if we look after our soil properly, we may not need to use it. As long as we can control harvest traffic, then there are big benefits in not going through with heavy machinery and cultivators.

“They are an additional cost with the potential to damage the soil.”

  • Written by: Farmers Guide
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