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11 Aug 2021

Tools to target weed seeds

As featured in Arable Farming Magazine

Tools to target weed seeds

by Arable Farming

Reducing working depth and cultivation passes should be a win-win for soil quality and the bottom line, but matching the approach and the armoury to the weed burden and conditions is proving key. Jane Carley reports.

Min-till establishment centres around cultivating just the top few inches of soil to conserve moisture, help combat weeds and cut tillage costs.

But opinions vary on exactly how much to cultivate, how deep to work and the timing of cultivations.

Disturbing the surface just enough to encourage weeds to chit for effective treatment with herbicides is key, says Matt Siggs, commercial technical manager (South West) for Bayer, which supplies glyphosate herbicide Roundup.

He says: Preparing the seedbed in two passes is the optimum, with NIAB trials having shown there is no extra control to be gained with any more.

We also have to be mindful to minimise the risk of glyphosate resistance by not overusing herbicides.

Choosing the right cultivation technique depends very much on the weed burden and weed species, he adds.

A light pass with a straw rake may be enough to get a chit, but bear in mind the influence of weed seed dormancy.

The objective is to get the seeds to chit forward so weeds can be tackled at the 1-2 leaf stage; you are less likely to get adequate control when they are tillering.

Brome is becoming an issue for more growers, for example, so knowing its germination habit is key, he says.

Chit Farmers should work closely with their agronomist so they are both prepared for what they are dealing with.

Where a rake does not produce the required chit, it is necessary to work a little deeper and he suggests this could be the right approach for black-grass this autumn.

Aim to work no deeper than the drill, say 3-5cm, so you can get the seedbank in this zone to germinate early and take the pressure off pre-em and post-em herbicide applications.

He says this is also an ideal time to tackle volunteers, such as spring barley, which can be a particular challenge in wheat.

Consideration does need to be given to retaining precious surface moisture and here soil type is an influence on how you cultivate and when.

n heavier soils, the operation can help to level off the surface and give something to drill into.

Mr Siggs also advises that a second pass should be at the same depth as the first.

Stay in the same zone and dont mix zones as this could bring up old material.

An Agrii trial involving 10 different min-till cultivators setting up 18 hectares of heavy clay ground in autumn for spring barley drilling has explored the savings offered by reducing tillage depth.

The trial at Roy Ward Farms, Leadenham, Lincolnshire, followed each strip cultivated in mid-September 2019 with detailed autumn and spring soil assessments through to 2020 crop yields and margins.

Carbon emissions It found cultivation costs could be more than halved from the farms established min-till regime without compromising spring barley yields, leading to improvements in both margins and carbon emissions.

Taking place on the farms heaviest field, with a clay content of more than 50% and around 30% silt, plus noticeable trafficking damage following the wet harvest, nine different min-till tine, disc and press combinations worked the field alongside Andrew Wards existing Simba Solo at depths varying from 175mm to just 50mm.

Soil structural and wetness assessments were made at two depths in the profile a month later and in early January; Laureate barley was sown at 400 seeds/sq.m on March 28 with the farms 10-year-old 8m Simba Freeflow drill; and the crop harvested on August 31, 2020.

Out of a possible maximum of 80, overall soil ratings from both assessments ranged from 18-45, highlighting major differences between the machines.

Interestingly, both the lowest and the highest scores came from some of the deepest cultivations and no real differences were evident between depth of working.

There was, however, clear evidence of smearing wherever the soil was worked too close to 200mm.

At the same time, shallower working did not always give the best straw mixing or soil structuring.

Yield across the cultivation regimes varied from 7.4-8.2 tonnes/ha, again with little clear association with depth of working.

In bottom line terms, though, shallower working gave noticeably higher margins over inputs and establishment costs.

Agrii trials manager Steve Corbett says: We saw an almost identical yield from the shallow est trial cultivation at just 50mm to add an extra £40/ha to the margin by lowering costs through faster working and lower fuel use.

And this was despite the fact that it was, arguably, less well-matched to the capabilities of the Freeflow drill than the established cultivation practice.

As well as the fact shallower cultivation can be appropriate for well-structured heavier soils, our assessments underlined the importance of both matching tine and disc spacing and configuration to working depth and the sort of press to soil type for the best results.

The spacing of the tines or discs across the cultivator governs the depth range over which it can still work the entire width of soil, shallower working needing closer spacing and vice versa.

Equally, the press determines how well the ground is reconsolidated, weather proofed and set up for restructuring over winter.

Full width cultivation Vaderstad marketing manager Andy Gamble also endorses a shallow approach to cultivations, working in the top 3-5cm.

Weed seeds remain below this level so its important not to bring them to the surface with any subsequent cultivations and to drill above them, he says.

Operators are looking to work at shallower depths, with wider implements and across their full width.

Mr Gamble suggests that using a tool such as the Vader stad Carrier, with its CrossCut ter disc going in just 3cm across the full width, avoids disturbing buried weed seeds while encouraging those close to the surface to chit.

While minimal disturbance is cited as a benefit of direct drilling, on many soil types, and in typically wet UK conditions, seedbeds are prone to compaction, leading to the need for a periodic ‘reset with the plough.

The problem is black-grass seeds can live for 15 years or so below the surface, so theres a risk of bringing them up after say, seven years.

A successful approach is to judge it on the seedbed, Mr Gamble suggests.

Clearance Choose a low disturbance leg if you need to work deep, which avoids bringing weed seeds to the surface.

Where the land is intend ed for spring crops, leaving it over winter allows the surface to weather, or you can establish a cover crop.

We would tend to drill straight into the sprayed off cover, with three rows of coulters on the Vaderstad Rapid drill offering plenty of clearance.

Mr Gamble says a direct seeding approach can work well in rotation where farms are trying not to over-cultivate.

But make sure you can close the slot creating a small amount of tilth can help, such as with the System disc on the front of the Rapid.

In the field R. Hill and Son, West Midlands

R.Hill and Son grow combinable crops on 750 hectares near Coventry, West Midlands, and tools to produce a seedbed depend very much on the conditions and soils, says David Hill.

We have relatively small fields, yet there can be several soil types in one field, he adds.

Our first Vaderstad Rapid drill came to the farm in 1994, so we have been fine tuning our stale seedbeds since then but have the advantage that it will also direct drill if conditions allow, or work into cover crops.

The drill also has Agrilla tines up front, so can create a tilth to ensure seed-to-soil contact.

The ideal would be to go in with the TopDown cultivator once, spray off and drill.

Some years the seedbed needs more, but in an autumn like last year there may be little opportunity.

The TopDown is an implement that can be operated at various depths depending on the conditions.

He adds that a Vaderstad Carrier also comes in useful for initial cultivations, shallow work and consolidation.

We have some black-grass and we will use rotational ploughing, but not too much.

We find that where the TopDown has been used, fields that have not been ploughed for 20 years are clean.

But it is important to look at the whole picture, he says.

The objective is to make a good seedbed with the least effort.

But for that to be successful you need to ensure drainage is good enough.

This can be as simple as clearing ditches out to connect with the drains that were laid on most farms in the 1970s and 1980s.

Theres a lot of new kit on the market, but it is expensive and commodity prices dont always justify the investment.

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