Experimental evaluation of biological regeneration of arable soil: The effects of grass-clover leys and arbuscular mycorrhizal inoculants on wheat growth, yield, and shoot pathology

Abstract

Wheat yields have plateaued in the UK over the last 25 years, during which time most arable land has been annually cropped continuously with short rotations dominated by cereals. Arable intensification has depleted soil organic matter and biology, including mycorrhizas, which are affected by tillage, herbicides, and crop genotype. Here, we test whether winter wheat yields, mycorrhization, and shoot health can be improved simply by adopting less intensive tillage and adding commercial mycorrhizal inoculum to long-term arable fields, or if 3-year grass-clover leys followed direct drilling is more effective for biological regeneration of soil with reduced N fertiliser. We report a trial of mycorrhization, ear pathology, and yield performance of the parents and four double haploid lines from the Avalon x Cadenza winter wheat population in a long-term arable field that is divided into replicated treatment plots. These plots comprised wheat lines grown using ploughing or disc cultivation for 3 years, half of which received annual additions of commercial arbuscular mycorrhizal (AM) inoculum, compared to 3-year mown grass-clover ley plots treated with glyphosate and direct-drilled. All plots annually received 35 kg of N ha−1 fertiliser without fungicides. The wheat lines did not differ in mycorrhization, which averaged only 34% and 40% of root length colonised (RLC) in the ploughed and disc-cultivated plots, respectively, and decreased with inoculation. In the ley, RLC increased to 52%. Two wheat lines were very susceptible to a sooty ear mould, which was lowest in the ley, and highest with disc cultivation. AM inoculation reduced ear infections by >50% in the susceptible lines. In the ley, yields ranged from 7.2 to 8.3 t ha−1, achieving 92 to 106% of UK average wheat yield in 2018 (7.8 t ha−1) but using only 25% of average N fertiliser. Yields with ploughing and disc cultivation averaged only 3.9 and 3.4 t ha−1, respectively, with AM inoculum reducing yields from 4.3 to 3.5 t ha−1 in ploughed plots, with no effect of disc cultivation. The findings reveal multiple benefits of reintegrating legume-rich leys into arable rotations as part of a strategy to regenerate soil quality and wheat crop health, reduce dependence on nitrogen fertilisers, enhance mycorrhization, and achieve good yields.

Sustainable soil management in the United Kingdom: A survey of current practices and how they relate to the principles of regenerative agriculture

“…We also recognize the limitations of a single regenerative agriculture score calculated in this way. For instance, using both no‐tillage and minimum‐tillage would give a similar score on the first principle to using no‐tillage and herbal leys, the latter is likely a more effective combination of practices for enhancing soil organic matter (Austen et al, 2022; Guest et al, 2022). Such limitations are inevitable when condensing complex “systems management” information into a simple, easy‐to‐interpret score.…”

“…No single definition of sustainable soil management exists, as different practices are required in different soil and agro‐ecological contexts (Miner et al, 2020). However, there is increasing recognition that sustainable soil management needs to encompass practices that can simultaneously improve soil biology, soil structure and nutrient status (Berdeni et al, 2021; Guest et al, 2022) and reduce reliance on expensive chemical inputs (Austen et al, 2022; LaCanne & Lundgren, 2018). Widely used soil conservation measures including contour cultivation, terracing, cover cropping, conservation tillage (minimum disturbance tillage) and no‐tillage (zero tillage or direct drilling) can extend soil lifespans, increasing these to over 10,000 years in 39% of soils (Evans et al, 2020).…”

“…Widely used soil conservation measures including contour cultivation, terracing, cover cropping, conservation tillage (minimum disturbance tillage) and no‐tillage (zero tillage or direct drilling) can extend soil lifespans, increasing these to over 10,000 years in 39% of soils (Evans et al, 2020). At the same time, many of these practices improve soil biology and health (Austen et al, 2022).…”

“…Increasing awareness of the economic impacts of soil degradation (Graves et al, 2015) and intensified economic pressures on farmers arising from input costs and yield plateaus (which are likely due to soil constraints) provide impetus for change. Farmers using conventional intensive cropping in short rotations have been facing increasingly intractable weeds, pests and diseases (Austen et al, 2022), compounded by extreme weather events that have led, somewhat belatedly, to both UK farmers and policymakers to recognize the need for a wider uptake of sustainable soil management. This is reflected in the 25 Year Environment Plan, which sets an objective for all soils in England to be managed sustainably by 2030 (Defra, 2018).…”