A comparison between ploughing and direct drilling for seedbed establishment produced equal wheat yield results in an Agrii project to support the company’s sustainability strategy, ‘Green Horizons*.’

The trial also monitored the effect of sub-soiling.

The ploughed winter wheat plots in the Agrii trial produced 11.3 tonnes/hectare in 2022, with the direct-drilled crop matching the result where sub-soiling had been used for seedbed preparation, reported project manager, Rob Bowes. Meanwhile, the figure fell to 9.8 tonnes/ha on the direct-drilled plots minus sub-soiling.

Nevertheless, there is much more to the picture than yield results alone, he commented.

The Northern Farmer: Green wheat crops, part of Agrii's trial

“The trial results were submitted to the ADAS’ ‘YEN Zero project,’ which aims to identify practices which reduce the farm’s carbon footprint. The direct-drilled plots performed better in terms of carbon emissions and they are also associated with lower input costs, compared with ploughing. Similar results were achieved a replicated trial in spring barley.

“A potential downside of direct drilling is that weed control requires greater attention, compared with plough-based establishment. The direct-drilled plots, which followed a winter cover crop, needed an additional application of glyphosate. This was necessary in order to reduce competition for the cereal crop. The main problem weed for the wheat was wild oats, while brome was the primary issue in the spring barley.”

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Nutrient use efficiency (NUE) is also being evaluated in the field-scale trials, added Mr Bowes.

“The Government is looking at NUE as part of the Sustainable Farming Incentive. The NUE assessment involves calculating nitrogen removed in the harvested crop (yield times grain nitrogen) divided by all nitrogen inputs. Soil mineral nitrogen levels in early spring is included, along with nitrogen estimated to be already in the crop, plus all inorganic and organic fertiliser inputs.

“The NUE calculation produces results in a percentage form and in our plots the figure for the conventional wheat was 82 per cent, with the direct-drilled crop at 87 per cent. Therefore nitrogen use efficiency was higher for direct drilling.

“However, in some instances direct drilling can result in greater quantities of straw being left behind after harvest. As much as 20-30kgs of nitrogen per hectare could be ‘locked up’ by soil microbes to break down the straw, but this is later released to become available to the plants. Therefore it is taken into account by estimating nitrogen in the spring crop.”

The Northern Farmer: The ploughed winter wheat plots in the Agrii trial produced 11.3 tonnes/hectare in 2022

Further Agrii research has pinpointed several other ‘top tips’ for successful direct drilling. These include going ahead with cultivation as soon as ground conditions permit, as this will allow maximum time for ‘weathering.’ Cultivators should be selected for their ability to produce clods of a size that will weather down well without slumping, particularly on soils with a high silt content. In addition, the land should only be work as deeply as is necessary to loosen the upper layers of soil, leaving the crop roots to achieve any deeper soil structuring that is required.

It is also essential to tackle any soil compaction ahead of direct drilling and deal effectively with any straw from the previous crop, said Mr Bowes.

“The baler should pick up as much straw as possible, to minimise the risk of slug damage in the following rotation. Straw chopper settings must be carefully calibrated, as excess material left on the surface can cause ‘scissoring’ at sowing time, with the disc pressing straw into the seed slot. This situation can lead to a negative effect on establishment levels.”

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The field-scale trials are based on a farm in County Durham. Two fields have been allocated for the project, with each field divided equally in half, he explained. This year, the wheat and barley fields have been reversed.

“The trial allows for a direct comparison between the two methods of crop establishment. We are also monitoring soil quality and have linked the evaluation with Agrii’s Soil Resilience Strategy (SRS), which is a research and development-based soil service. It combines physical, chemical and biological soil assessments and gives the results a scientific interpretation.

“The results from farms participating in the SRS are benchmarked against other businesses, while individual farm progress can be monitored from year to year. We aim to monitor the effect of varying establishment methods on the County Durham trial farm on soil quality over an extended period. The unit has a 30-year history of traditional seedbed preparation through the use of the plough, followed by a power harrow and then a combination drill.

“I would stress that the comparison between plough-based establishment methods and direct drilling does not set out to find evidence to persuade farmers to adopt direct drilling on a widespread scale or vice-versa. The idea is simply to compare productivity between the two systems and discover more about their effects on soil quality,” said Mr Bowes.

* Launched in 2019, Green Horizons is Agrii’s framework for supporting a sustainable farming future.