Assessing the Impact of Zero Tillage on Agrochemical Transport

Soil is the most complex biomaterial on earth, yet our understanding of how its form influences its function is still poorly understood. This is large due to our inability to observe what is happening underground as soil is opaque. However, new methods to image soil systems, using tools such as X-ray Computed Tomography now provide a means to explore this hidden underworld. Soil is the largest land-based reservoir of carbon on Earth. Changes in the management of agricultural soils can affect their role as a source or sink in the global carbon cycle, and the scale and composition of their greenhouse gas emissions. Conservation Agriculture approaches such as those that reduce cultivation are gathering pace in adoption globally. There is increasing evidence that by reducing or ceasing to plough (i.e. zero tillage), a soil structure evolves, over time, which improves soil health/quality whilst maintaining crop yield. Recent data has shown there are also advantages in terms of reduced greenhouse gas emissions and enhanced carbon sequestration. While the adoption of zero tillage in N. & S. America has been rapid, Europe, and in particular, the UK, has been slower to respond with currently only c. 50% under min tillage and around 10% under zero tillage. Evidence that outlines the implications for the adoption of zero tillage in the UK is urgently needed. New evidence that outlines the implications for the adoption of zero tillage in the UK is urgently needed.

A key area not yet assessed is the impact of tillage on the bio-performance of soil applied agrochemicals despite empirical evidence from the field indicating product performance is indeed affected. Zero tillage substantially increases bulk density and subsequently decreases soil porosity which impacts negatively on the infiltration of water and solutes, including agrochemicals. However, the impact of leaving the soil undisturbed is the development of a soil structure, over time, driven by the soil fauna. This structure has a reduced porosity compared to ploughed soil but a comparable pore connectivity which is the most important property for soil hydraulic function.

The overarching aim is to illustrate how, and over what time scales, soil structure obtained under zero tillage impacts on agrochemical product performance. In partnership with Syngenta, and using a combination of field and laboratory work, key questions that this exciting PhD project will assess include: i) What is the impact of the soil structure imposed by zero tillage on the distribution and movement of agrochemicals in soil; ii) To what extent are differences persistent across soil types; iii) How do differences in soil structure affect the bio-performance of agrochemicals and iv) At what point, if any, in the conversion from conventional to zero tillage do soil hydraulic properties favour optimum availability of agrochemicals in soils.