Do cover crops increasethe resilience and sustainability of the agri-food system?

世界上超过三分之一的土壤资源退化，影响了粮食生产。包括环境变化在内的其他未来威胁也将影响土壤系统提供各种生态系统服务的能力，包括粮食生产。我们在农业系统中有土壤管理工具可以减少土壤退化，但对于这些工具是否可以提高土壤对这些未来威胁的适应能力，我们知之甚少。覆盖作物（在可耕地轮作中在经济作物之间种植的作物，以提供环境效益）就是这样一种工具，它产生的生物量进入土壤，为土壤食物网提供食物。覆盖作物提供了一种易于处理的方法来增加可耕地景观的植物多样性，因为可以同时种植对比物种的混养，而不改变经济作物的农艺管理。覆盖作物混养可包括彼此提供不同环境益处的植物，并且包括来自产生不同植物次级代谢物的不同植物科的物种。然而，目前尚不清楚在何种程度上所产生的生物质的生物化学多样性，进入共享的根际和碎屑层的混养结果的相互作用，形成土壤食物网的结构，形成一个社区，更有能力提供土壤功能和确保对环境变化的恢复能力比混养的单个成员的总和。首要的假设是，增加植物多样性覆盖作物混养的土壤食物网的反应，提供更大的土壤对环境变化和短期扰动的恢复力。这一假设是证实，因为当提供一个单一的来源的作物残留物和根系分泌物的土壤，一个食物网，是最适合利用该资源将被激活，但当应用的几个生物化学对比基板的混合物，生态位的数量增加和群体的生物体能够竞争性地利用这些小生境被刺激。这一假设将通过在实验室规模、田间小区规模和景观规模进行实验来检验，其目标如下：1.确定复合栽培是否改变了土壤食物网，提供了更大的土壤功能，并增加了经济作物产量，与各部分的总和相比，2.确定复合培养是否能使土壤微生物群落更具弹性3.调查土壤类型对覆盖所提供的效益的影响农作物混作田间小区规模：这个博士项目将利用并延长在Sonning的阅读大学实验农场已经建立的田间实验的寿命。Berseem三叶草、荞麦、油萝卜和向日葵每年在地块中作为单一物种单作或作为秋播谷类作物之间的四季混栽轮流种植。将每年测量土壤微生物、中型动物和大型动物群落的生物量、组成和活性及其与土壤结构、养分供应和作物产量的关系，以实现目标1。实验室规模：将在上述田间实验的地块上安装开顶箱，以模拟与英国预计环境变化一致的冬季变暖和夏季热浪。将使用实验室呼吸计和最新的方法定期测定地下室和邻近室的土壤恢复力，以量化土壤恢复力，以实现目标2。景观规模：将招募一个农民网络，对整个景观中的对比土壤类型进行实地试验。

Over a third of the World's soil resources are degraded, compromising food production. Additional future threats including environmental change will also affect the capability of soil systems to deliver a variety of ecosystem services, including food production. We have soil management tools available in agricultural systems to reduce soil degradation yet there is little understanding whether they can increase soil resilience in light of these future threats. Cover crops (crops grown between cash crops in an arable rotation to provide environmental benefits) are one such tool which generates biomass that enters the soil and feeds the soil food web. Cover crops offer a tractable means to increase the botanical diversity of arable landscapes because a polyculture of contrasting species can be simultaneously cropped without changing the agronomic management of the cash crop. Cover crop polycultures can comprise plants that provide different environmental benefits to one another and include species from different plant families that produce different plant secondary metabolites. However, it is unclear to what extent the resulting biochemical diversity of the biomass that enters the shared rhizpsphere and detritosphere of a polyculture results in interactions that shape the structure of the soil food web to form a community that is more capable of delivering soil functions and securing resilience against environmental change than the sum of the individual members of the polyculture. The overarching hypothesis is that increased plant diversity in cover crop polycultures results in a soil food web response that provides greater soil resilience to environmental change and short term perturbations. The hypothesis is justifiedbecause when providing a single source of crop residues and root exudates to a soil, a food webthat is most adapted to exploiting that resource will be activated, but when applying a mixture of several biochemically contrasting substrates, the number of ecological niches increases and groups of organisms capable of competitively exploiting each of these niches are stimulated. This hypothesis will be tested by conducting experiments at the laboratory scale, field-plot scale, and the landscape scale with the following objectives: 1.Identify whether polycultures alter soil food webs, provide greater soil functions, and increase cash crop yield, compared to the sum of the parts, or a control.2.Determine whether polycultures engineer more resilient soil microbial communities 3.Investigate the impact of soil type on the benefits provided by cover crop polyculturesField-plot scale: This PhD project will make use, and extend the lifetime, of an already established field experiment on the University of Reading experimental farm at Sonning. Berseem clover, Buckwheat, Oil radish and Sunflower are grown annually in plots either as single species monocultures or as a quaternary polyculture between autumn-sown cereal crops in rotation. Annual measurements of the biomass, composition and activity of the soil microbial, mesofauna, and macrofauna community and its relationship with soil structure, nutrient availability and crop yield will be made to address Objective 1.Laboratory scale: Open top chambers will be installed on the plots of the field experiment described above to simulate winter warming and summer heatwaves consistent with projected environmental change in the UK. The resilience of soil from underneath and adjacent to the chambers will be assayed periodically using a laboratory respirometer and a recent methodology to quantify soil resilience to address Objective 2. Landscape scale: A network of farmers will be recruited to establish field trials on contrasting soil types across a landscape.