Knowledge is growing on how tillage practices and cover crops impact on soils and water but results are not always predictable.
Shallow non-inversion tillage gave comparable economic performance to plough-based systems, while direct drilling resulted in a six per cent decline in profits relative to conventional practice, according to trials carried out by the University of East Anglia at Salle Park Estate, Norfolk.
The four-year (2013-2017) cultivation trial, conducted as part of the Demonstration Test Catchments (DTCs) research platform established by Defra, looked at the impact of contrasting tillage regimes on the biological, chemical and physical condition of soils.
Working across nine fields, covering 143ha of arable land in the same year of a seven-year rotation, three contrasting tillage regimes were established, explained Prof Andrew Lovett of UEA at the Harper Adams University Soils and Water conference. “Block J was conventional mouldboard ploughing to a 25cm depth; block P was shallow non-inversion to 10cm depth using the disks and tines of a Vaderstad Topdown and Carrier and Block L was direct drilling with zero inversion using a Vaderstad Seed Hawk direct drill.”
Reduced tillage had no significant effect on soil bulk density, a measure of compaction, compared with a plough-based system, did not significantly improve soil organic carbon content or significantly alter soil nutrient status, according to Prof Lovett.
A key aspect of the tillage trials was to assess what impact reduced cultivations had on nutrient leaching losses from arable land into the River Wensum. “The greatest distinction between blocks occurred during the cover crop year (2013-2014) where nitrate leaching losses were 75 per cent lower under shallow non-inversion with a cover crop and 88 per cent lower under direct drill with a cover crop than under plough with fallow [stubble].
“During the subsequent three years, when only reduced cultivations were trialled (no cover crops) there was no significant distinction in nitrate leaching losses between blocks.”
The research also looked at earthworm populations as a measure of soil health. Prof Lovett said: “In contrast to expectations, average earthworm populations were larger under the plough based system in clay loam, sandy loam and sandy silt loam soils than either of the reduced tillage blocks. Only in sandy clay loam soils were earthworm numbers marginally higher under direct drill.
“It can therefore be concluded that reduced cultivations did not improve earthworm populations.”
Total profit margins over the four-year period were £3,365/ha under shallow non-inversion tillage, £3,314/ha under plough and £3,114/ha under direct drill. “Shallow non-inversion yielded comparable economic performance to the plough based systems, while direct drilling resulted in a small decline in profits relative to conventional practice,” said Prof Lovett.
Salle Farms has now applied the shallow tillage system across its entire arable area, according to Prof Lovett.
Early findings of the Maxi-Cover Project led by ADAS show that early establishment of cover crops is essential to ensure good cover and maximum benefits.
Paul Lewis, senior lecturer in soil and environmental science at Harper Adams University, summarised research on cover crops, identifying knowledge gaps.
As well as early establishment of cover crops, the earlier in August, the better, according to Mr Lewis, the Maxi-Cover Project has shown that increased rooting in the cover crop may increase rooting in the following spring crop, provided the spring crop establishes well. However, it also found that cover cropping can increase moisture retention in the topsoil which may impede establishment of following spring crops.
The project, which runs until next year, is looking at 10 cover crop treatments – straights and mixes -at three sites in Cambridgeshire, Nottinghamshire and Yorkshire. Commercial farm validation trials are also being conducted. It measures soil properties including moisture, organic matter, earthworms, P, K, Mg, crop rooting and subsequent crop yield.
Mr Lewis said research gaps remained in terms of identifying suitable cover crop species for different soil types, cover crop options matched to cultivation options, N release post-destruction in relation to following cash crop establishment, nutrient availability following destruction by grazing, and impact of covers on weed populations in the following cash crop and throughout the rotation.
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