Regenerative agriculture effects on biomass, drought resilience and 14C-photosynthate allocation in wheat drilled into ley compared to disc or ploughed arable soil

Abstract

Regenerative agriculture practices including leys and no-tillage facilitate biological reassembly of soil aggregates, increasing water, carbon and nutrient storage, but how this effects crop biomass, photosynthate partitioning, and drought resilience is unclear. To address this, we took monoliths growing semi-dwarf and taller wheat genotypes from 3-year plots that were ploughed or disc cultivated, or direct-drilled into a grass-clover ley and applied 35 kg N ha-1. Half the monoliths received a spring drought, then all were watered and the wheat 14CO2 pulse-labelled at stem elongation. The ley soil had lower bulk density, stored more water, and the taller wheat genotype maintained 8-fold higher proportion of water-stable macroaggregates despite unexpectedly having the smaller root biomass. Yields on the ley soil (3.74 t ha-1) were 77% -123% higher than on ploughed and disc cultivated soils, and unaffected by genotype or drought, despite its >70% reduction in root biomass. Of the 14C initially retained in wheat, 72% was in shoots, with root allocation decreasing by 75-90% in droughted ley soil, and at harvest soil retained <1% of the 14C, with significantly lower values for taller wheat, and ley. We conclude that soil health regeneration in the ley enhanced wheat yields, but reduced photosynthate allocation to root biomass under drought. Although taller wheat maintained better macroaggregation in ley soil, this was not explained by root biomass or photosynthate allocation and unexpectedly failed to increase soil 14C sequestration. We find no evidence that ley regeneration of macroaggregation enhances soil C sequestration under wheat, despite higher yields.