Assessing the Impact of Zero Tillage on Agrochemical Transport

土壤是地球上最复杂的生物材料，但我们对其形态如何影响其功能的理解仍然知之甚少。这很大程度上是因为我们无法观察地下发生的事情，因为土壤是不透明的。然而，利用x射线计算机断层扫描等工具对土壤系统进行成像的新方法，现在为探索这个隐藏的地下世界提供了一种手段。土壤是地球上最大的陆地碳库。农业土壤管理的变化可以影响其在全球碳循环中作为源或汇的作用，以及其温室气体排放的规模和组成。诸如减少种植的保护性农业方法正在全球范围内加速采用。越来越多的证据表明，通过减少或停止耕作（即零耕作），土壤结构会随着时间的推移而演变，从而改善土壤健康/质量，同时保持作物产量。最近的数据显示，在减少温室气体排放和加强碳固存方面也有优势。虽然北美和南美采用免耕的速度很快，但欧洲，特别是英国，反应较慢，目前只有50%的土地采用少耕，10%左右采用免耕。英国迫切需要证据来说明采用零耕作的影响。英国迫切需要新的证据来概述采用零耕作的影响。尚未评估的一个关键领域是耕作对施用农用化学品的土壤生物性能的影响，尽管来自实地的经验证据表明产品性能确实受到影响。免耕大大增加了容重，随后降低了土壤孔隙度，这对水和溶质（包括农用化学品）的渗透产生了负面影响。然而，保持土壤不受干扰的影响是土壤结构的发展，随着时间的推移，由土壤动物驱动。与耕地相比，这种结构的孔隙率降低，但孔隙连通性相当，这是土壤水力功能最重要的特性。总体目标是说明如何，以及在什么时间尺度上，在零耕作下获得的土壤结构对农化产品性能的影响。通过与先正达公司的合作，并结合现场和实验室工作，这个令人兴奋的博士项目将评估的关键问题包括：i)免耕对土壤结构对土壤中农用化学品的分布和移动的影响；ii)不同土壤类型之间的差异在多大程度上持续存在；iii)土壤结构的差异如何影响农用化学品的生物性能；iv)在从传统耕作到零耕作的转变过程中，如果有的话，在什么时候土壤的水力特性有利于土壤中农用化学品的最佳可用性。

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.