Article taken from the Tillage Magazine
Until quite recently, over winter cover crops within arable rotations have had two main roles – boosting soil organic matter levels and soaking up nutrients be leached from bare land.
Now, however, they are seen as offering several other benefits, not least countering burgeoning black grass infestations.
There are plenty of opportunities for cover crops and Paul Brown of Frontier Agriculture and Kings believes they can help address the apparent plateauing of wheat and oilseed rape yields.
Average wheat yield has plateaued
Despite the use of improved varieties and pesticides, average wheat output – about 8t/ha in 2002 – had fallen below 7t/ha by 2012 and rose only slightly above 8t/ha last harvest, he notes.
“I firmly believe that many soils are in poor health, in other words not as biologically active as they should be, and are badly structured. Introducing cover crops carefully into the rotation can help overcome this.
Mr Brown highlights the importance of capturing nutrients left over from previous crops, especially nitrogen at risk of leaching.
At best only 70% of nitrogen fertilizer applied to cereals is used by the crop and on medium and clay soils as much as 40% may remain unused after harvest, he points out.
Lower than optimum yields, manure applications and warm autumns which increase mineralisation in the soil all potentially raise the amount of nitrogen available for cover crops to capture.
The company’s monitoring on six heavy land sites in Bedfordshire found that the average loss in 2013 between September and the end of the year was 57kg N/ha – a year earlier over the same period it was as high as 78kg N/ha.
Mr Brown points to a University of East Anglia snap-shot of field drain outfalls. It found that between October and December 2013 the mean nitrogen loss to the drain water was about 18mg/litre where the land was ploughed and left unsown or drilled with winter wheat, but averaged only 2.6mg/litre where an oil radish cover crop had been sown.
“Essentially it showed that bare land loses nitrogen at five times the rate as cover cropped land. A lot of that nitrogen has been paid for.” He stresses.
“Many growers don’t realise how leaky nitrogen is in the soil and how inefficient most cereals are at capturing and using it. The case for cover crops suddenly becomes more viable when growers realise how much nitrogen is potentially being lost through their water systems.”
Kings is running a series of trials to assess how much nitrogen various cover crops may capture and the results in table A are typical, he says.
Agrovista’s Chris Martin believes the key to using cover crops effectively is to choose the most appropriate mix for the specific purpose, be it soil conditioning, nutrient trapping, fumigation to tackle soil pests, or weed suppression.
“There’s certainly no one mix available which suits all needs,” he stresses.
“We’re looking at a wide range of cover crops to satisfy each and all of these purposes throughout the UK, but I think our most innovative work is where we are using specific covers to help control resistant blackgrass and ryegrass.”
Theory suggests that a black oat and vetch mix should provide several benefits, he says.
“Firstly we’re looking to condition and dry out the soil to introduce drilling windows after the peak blackgrass germination period.”
This should allow autumn crops to be sown later or enable spring crops to be sown on heavy land where neither activity would usually be possible, he explains.
Encourage germination
“The idea is to encourage as much blackgrass to germinate amongst the cover crop as possible.”
Mr Martin points out that the approach differs from others where cover crops are intended to compete with or smother blackgrass, and it has given promising results.
“In establishing the cover crop we employ vigorous cultivation to encourage blackgrass germination. Everyone knows that the biggest blackgrass flush occurs when we put the drill in the field regardless of stale seedbeds.
“The black oat and vetch mix is also slow to colonise the ground which allows a good blackgrass flush.
“Once the cover crop is established, its massive root structure allows further light cultivation, using a straw rake for example, to encourage a further blackgrass strike.”
Before drilling the late autumn or spring crop, a split glyphosate application is employed. The first destroys the cover crop, and the second, ten days later, ensures that any shaded blackgrass is killed, he explains.
Direct drill
“We then drill straight into the cover crop using a disc coulter drill with as little disturbance of the soil as possible to avoid setting off another flush of blackgrass.
“We’ve successfully used several drills to achieve this including direct drills such as the Great Plains Spartan and the Moore Uni. We’re also working this season with strip till drills such as the Claydon.
“We’re also trying cultivator drills, such as the Vaderstad Rapid, getting lower soil disturbance by lifting the cultivation elements out of the ground, and using just the disc coulters.
“Last year’s results demonstrated a dramatic reduction in blackgrass numbers in the following crop without herbicides.”
Spring wheat plots after fallowing and several stale seedbeds throughout the autumn and winter ended up with 55 blackgrass heads/sq m at harvest, he notes.
“This was still a great reduction on the neighbouring winter wheat plots which despite having received and extremely robust herbicide programme often still had several hundred blackgrass heads per square metre at harvest.
“However, the spring wheat following the black oat and vetch cover crop had less than two blackgrass heads per square metre at harvest and yielded an impressive 8.6t.ha.”
Cover crop establishment best practice
- Sow as soon as possible after harvest
- Use minimal cultivations
- Direct drilling is ideal
- Consider seed-bed starter fertiliser
- Monitor slugs and flea beetles
- Use high seed rates
- Aim to maximise crop biomass
Until quite recently, over winter cover crops within arable rotations have had two main roles – boosting soil organic matter levels and soaking up nutrients be leached from bare land.
Now, however, they are seen as offering several other benefits, not least countering burgeoning black grass infestations.
There are plenty of opportunities for cover crops and Paul Brown of Frontier Agriculture and Kings believes they can help address the apparent plateauing of wheat and oilseed rape yields.
Average wheat yield has plateaued
Despite the use of improved varieties and pesticides, average wheat output – about 8t/ha in 2002 – had fallen below 7t/ha by 2012 and rose only slightly above 8t/ha last harvest, he notes.
“I firmly believe that many soils are in poor health, in other words not as biologically active as they should be, and are badly structured. Introducing cover crops carefully into the rotation can help overcome this.
Mr Brown highlights the importance of capturing nutrients left over from previous crops, especially nitrogen at risk of leaching.
At best only 70% of nitrogen fertilizer applied to cereals is used by the crop and on medium and clay soils as much as 40% may remain unused after harvest, he points out.
Lower than optimum yields, manure applications and warm autumns which increase mineralisation in the soil all potentially raise the amount of nitrogen available for cover crops to capture.
The company’s monitoring on six heavy land sites in Bedfordshire found that the average loss in 2013 between September and the end of the year was 57kg N/ha – a year earlier over the same period it was as high as 78kg N/ha.
Mr Brown points to a University of East Anglia snap-shot of field drain outfalls. It found that between October and December 2013 the mean nitrogen loss to the drain water was about 18mg/litre where the land was ploughed and left unsown or drilled with winter wheat, but averaged only 2.6mg/litre where an oil radish cover crop had been sown.
“Essentially it showed that bare land loses nitrogen at five times the rate as cover cropped land. A lot of that nitrogen has been paid for.” He stresses.
“Many growers don’t realise how leaky nitrogen is in the soil and how inefficient most cereals are at capturing and using it. The case for cover crops suddenly becomes more viable when growers realise how much nitrogen is potentially being lost through their water systems.”
Kings is running a series of trials to assess how much nitrogen various cover crops may capture and the results in table A are typical, he says.
Agrovista’s Chris Martin believes the key to using cover crops effectively is to choose the most appropriate mix for the specific purpose, be it soil conditioning, nutrient trapping, fumigation to tackle soil pests, or weed suppression.
“There’s certainly no one mix available which suits all needs,” he stresses.
“We’re looking at a wide range of cover crops to satisfy each and all of these purposes throughout the UK, but I think our most innovative work is where we are using specific covers to help control resistant blackgrass and ryegrass.”
Theory suggests that a black oat and vetch mix should provide several benefits, he says.
“Firstly we’re looking to condition and dry out the soil to introduce drilling windows after the peak blackgrass germination period.”
This should allow autumn crops to be sown later or enable spring crops to be sown on heavy land where neither activity would usually be possible, he explains.
Encourage germination
“The idea is to encourage as much blackgrass to germinate amongst the cover crop as possible.”
Mr Martin points out that the approach differs from others where cover crops are intended to compete with or smother blackgrass, and it has given promising results.
“In establishing the cover crop we employ vigorous cultivation to encourage blackgrass germination. Everyone knows that the biggest blackgrass flush occurs when we put the drill in the field regardless of stale seedbeds.
“The black oat and vetch mix is also slow to colonise the ground which allows a good blackgrass flush.
“Once the cover crop is established, its massive root structure allows further light cultivation, using a straw rake for example, to encourage a further blackgrass strike.”
Before drilling the late autumn or spring crop, a split glyphosate application is employed. The first destroys the cover crop, and the second, ten days later, ensures that any shaded blackgrass is killed, he explains.
Direct drill
“We then drill straight into the cover crop using a disc coulter drill with as little disturbance of the soil as possible to avoid setting off another flush of blackgrass.
“We’ve successfully used several drills to achieve this including direct drills such as the Great Plains Spartan and the Moore Uni. We’re also working this season with strip till drills such as the Claydon.
“We’re also trying cultivator drills, such as the Vaderstad Rapid, getting lower soil disturbance by lifting the cultivation elements out of the ground, and using just the disc coulters.
“Last year’s results demonstrated a dramatic reduction in blackgrass numbers in the following crop without herbicides.”
Spring wheat plots after fallowing and several stale seedbeds throughout the autumn and winter ended up with 55 blackgrass heads/sq m at harvest, he notes.
“This was still a great reduction on the neighbouring winter wheat plots which despite having received and extremely robust herbicide programme often still had several hundred blackgrass heads per square metre at harvest.
“However, the spring wheat following the black oat and vetch cover crop had less than two blackgrass heads per square metre at harvest and yielded an impressive 8.6t.ha.”
Table A – Cover Crop Performance
Crop
Fresh
weight t/ha
Dry
Weight t/ha
%N
Total N
Kg/ha
Oil Radish
24.7
2.7
4.13
115
Winter Turnip Rape
19.5
2.8
3.1
88
Mustard
16.7
2.3
3.1
72
Vetch/rye
19.5
2.2
2.7
60
Kings Vitality mix
22.1
2.6
2.5
67
Kings Structure mix
20.6
3.5
2.0
72
Source: Kings trial Autumn 2014 Essex –
Above ground harvest 18th December
Table B – Impact on blackgrass population
Crop
Fresh
Weight t/ha
DM
t/ha
%N
Nitrogen
kg/ha
Potash
kg/ha
Blackgrass
Plants/sq m
Siletina Radish
39.8
4.93
4.6
227
204
4
Defender Radish
31.5
3.02
4.8
147
171
0
Mustard
33.6
6.72
3.52
236
212
103
Winter Turnip Rape
26.9
3.55
3.35
119
163
0
Strigosa Oat
11.4
2.34
2.84
66
62
202
Bare land
4.7
1.45
2.44
35
23
268
Wheat
6.6
1.63
2.9
47
38
504
Source: Kings 3D site, Alford, Lincs 15th January
Cover crop establishment best practice
- Sow as soon as possible after harvest
- Use minimal cultivations
- Direct drilling is ideal
- Consider seed-bed starter fertiliser
- Monitor slugs and flea beetles
- Use high seed rates
- Aim to maximise crop biomass