Abstract/Summary

Communicating the importance and value of the soil has never been more urgent. The soil is a foremost resource supporting human society, facilitating food and fibre production, protecting against drought and flood, cycling nutrients, harbouring functioning biodiversity and storing carbon. Yet soil degradation is one of the greatest threats to our future, as it diminishes these soil functions. This thesis assesses the viability of a sustainable approach to soil regeneration, while maintaining the productive function. A five-year experiment was set up on-farm, in an existing organic and biodynamic crop rotation, to explore the impact of in-situ grown biomass used as edaphic food. A standard treatment included plant necromass and root exudates from a rotation of 2-year diverse (23 species) ley, combinable crops, and green manure all constituted biomass input; an enhanced treatment retained crop residues in addition. Comparisons to a 5-year diverse ley and a fallow were also made. Soil health, weed burden and crop production were monitored to follow the change in, and outcomes of, soil function, over this period. Soil organic matter increased in the crop rotation whether crop residues were retained or not. The five years diverse ley resulted in a larger increase in soil organic matter, and bulk density and aggregate stability compared to the other treatments. The amount of organic matter in the top 100 mm of soil increased by between 1.21% and 3.14% yr-1 in the biomass input treatments and at the 100-300 mm depth by between 0% and 1.57% yr-1. These outcomes easily surpass the COP21 target of 0.4% annual increase in soil organic carbon stock, at the 0-100 mm soil depth with no loss or greater at the 100-300 mm depth. An increase in biodiversity was found when adding the biomass rather than removing it; soil mesofauna counts increased by 33% with retaining crop residues from combinable crops. These findings demonstrate important ecosystem services that could be provided by adding biomass to the soil. Mesofauna are multifunctional soil organisms, processing leaf litter, consuming pathogenic fungi, supplying nutrients available for plants and playing an important role in the carbon cycle. Weed burden did not change between treatments in crops. Weeds can limit crop production but also provide valuable flowers for insect pollinators, shelter and food for insects, small mammals, and birds, together with root diversity for improved soil root community dynamics. There was no change to yield from retaining crop residues. This study found that farm ecological performance can be improved by returning crop biomass to the soil, and diverse leys can store globally important quantities of soil carbon, this is both a climate change mitigation and adaptation strategy.