Allerton Project Conservation Agriculture

Conservation Agriculture

Direct drilling can help stabilise and protect the soil. © Alastair Leake/GWCT

BACKGROUND

The Allerton Project Farm is part of a network of five European farms looking at three different approaches to arable cropping over a five-year period. The results will indicate the economic and environmental impact of each of the systems. The transformation of natural habitat to agricultural land involves the clearance of the native vegetation and a repurposing of the soil, traditionally achieved through inverting the top-soil using the mouldboard plough. In natural systems, soils are relatively immobile and although even in stable habitats low levels of soil erosion are normal, most movement occurs through activities of macro-invertebrates, such as earthworms, that ‘churn’ the soil in situ.

Repeated annual ploughing in cropping systems produces a more homogeneous ‘tilth’ which is conducive to even crop germination and onward growth. But using a plough to create an aerated seedbed also gives rise to oxidation of the essential organic matter component, built up by years of deposition of decaying plant material. This loss of soil organic matter depletes fertility and structure while making the soil more vulnerable to erosion, capping, compaction, water-logging and drought – all things which are detrimental to crop production. It is, however, useful in burying freshly shed weed seeds and crop volunteers to a depth which precludes their germination in the subsequent crop.

In some climates, particularly in the Americas, ploughing has rendered large swathes of land uncroppable and farmers abandoned the use of the plough. Farmers found that if they combined three key practices they could stabilise and protect their soils: 1. Minimum soil disturbance pre-sowing and through the cropping season. This is done by using so-called ‘direct drills’ – crop seeders which slot the following crop seed into the previous crop’s stubble. 2. Maximum soil cover. Farmers seek to ensure that at no time is the soil surface left bare. This is done by chopping the crop residues at harvest and spreading them on top of the stubble, and/or by sowing fast-growing ‘cover crops’ during the intercrop period. This protects the soil against erosion by proving a protective ‘armour’. 3. Practising a diverse crop rotation. Different crops have different rooting characteristics, while their residues decompose over different lengths of time, both of which help to provide increased soil protection. Farmers switching to Conservation Agriculture (CA) techniques have also noticed other benefits arising in time, including a dramatic increase in earthworms, better soil structure and nutrient recycling, better rainfall infiltration and greater crop resilience during times of drought, a decrease of up to 70% in tractor fuel usage and an increase in soil carbon at the soil surface.

As we become more aware of the adverse impacts of food production on the health of the planet, it becomes increasingly important that we understand the full

KEY FINDINGS

life cycle impact of the measures we employ to cultivate crops. In 2017 the Allerton Project joined up with global crop protection experts Syngenta to begin an ambitious five-year, full-rotational trial into CA, comparing it with conventional and intermediate approaches. In 2018 we were joined by sister-sites in Kent, France and two farms in Spain. The breadth of data being gathered is the most detailed we have ever obtained, including environmental, soil, agronomic and profit metrics. After just three harvests there are some clear differences developing between the systems, including marked differences in winter foraging by farmland birds, which tend to prefer the direct-drilled stubbles, and the prevalence of different weed species within the systems.

Herein lies a future challenge because weeds are effectively controlled by the use of the herbicide glyphosate, which is threatened with regulatory withdrawal in the near future. The loss of this key tool within the CA system could result in large-scale reversion back to ploughing and consequences for the whole range of benefits we are recording. Hence the importance of our studies – we need to understand the full impact across a range of parameters to ensure we make the most informed, and best, decisions.

More skylarks were counted consistently on the lower tilled plots. © David Mason

Ploughing causes the loss of soil organic matter which depletes fertility and structure, making the soil more vulnerable to erosion, capping, compaction, water-logging and drought. © Peter Thompson

Bird numbers and greenhouse gas emissions from soils differed according to crop establishment cultivations.

Profitability is driven by a combination of crop output, variable and fixed costs.

Alastair Leake