Climate-smart grazing to restore tropical soils

问题陈述退化景观的恢复日益被视为一种可持续的投资，引发了全球对恢复生态系统土壤功能的大规模承诺。一个关键的前提是，优化放牧可以导致草原中的净碳（C）固存，足以抵消牲畜介导的甲烷（CH 4）排放。对具有多年生植被和“最佳”放牧率的草地的管理被推广为对土壤的气候智能型管理1。然而，不同的草地和牲畜管理方法对温室气体交换的净影响，特别是在热带地区，存在很大的不确定性。目前对土壤净碳吸收的估计可能高估了100%2。相互作用的因素决定了草地是否成为汇或源的C，其中放牧压力，土壤类型和降雨量发挥根本作用3。牲畜品种和放牧管理控制土壤碳和常量营养素的输入，通过选择性放牧，排泄物沉积，对土壤暴露和侵蚀的影响。模型可用于了解不同牲畜管理对土壤净温室气体交换的总体影响4，但需要数据来减少集约草地系统的不确定性。国际热带农业中心（热带农业中心）最近汇编了1980年代以来进行的草原调查和实验的土壤和植物生物量数据，并要求进行研究合作，以开发代表净排放系数关键控制的简单模型。该数据集包括广泛的土壤质地、气候带和放牧做法。该项目的目的是利用这一资源，结合系统的审查和一些经验性工作，开发简单的统计和过程模型，代表在哪里以及如何恢复热带草原可以提供净固碳。这将有助于综合景观规划。该项目将整理拉丁美洲热带草原的经验证据，确定草原在何种条件下成为碳汇，因此可能适合于景观恢复。该研究将结合联合收割机领域的水平，与实验室操作的机制研究，参数化和测试现有的土壤模型。研究将分四个阶段进行：1。本文通过文献综述和模型试验来估计土壤和放牧管理对土壤碳的影响程度。学生将对热带草原进行系统的文献综述，并访问哥伦比亚CIAT实验的广泛数据库。结果将用于建立简单的生态系统模型，如N14 CP 5，保留一些数据集用于模型测试。统计分析将用于评估主要因素和相互作用。外勤工作。学生将开发实验和/或调查设计，以填补评估现有数据库后变得明显的知识差距。支持过渡委员会可以在哥伦比亚的利亚诺斯提供实地地点，这些地点的土壤质地、深度和有机物质含量有很大差异，并实行季节性、永久性和轮流放牧管理。监督小组将协助进行实验设计和方法，以评估碳储存（至1米深度）和植被（CO2）和土壤（CO2和CH 4）中的通量。3.操纵实验根据数据审查和建模研究的结果，学生将选择控制C分解的关键因素，如土壤质地，常量营养素输入（主要是N和P）和水势，并进行旨在弥合剩余知识差距的实验室孵化。情景分析。开发的模型和关系将被用来评估在退化土地上，在土壤和管理的限制下，可以实现碳的净固存。

Problem statementThe restoration of degraded landscapes has increasingly been promoted as a sustainable investment, sparking large-scale global commitments to restore soil functions in ecosystems. A key premise is that optimisation of grazing can lead to net carbon (C) sequestration in grasslands, sufficient to offset livestock-mediated methane (CH4) emissions. Management of grasslands with perennial vegetation and 'optimal' stocking rates is promoted as climate-smart management of soils1. However, there is much uncertainty as to the net effects on greenhouse gas exchange of different grassland and livestock management approaches, particularly in tropical regions. Current estimates of net C uptake in soils may be overestimated by 100%2. Interacting factors determine whether grasslands become sinks or sources of C, among which grazing pressure, soil type and rainfall play fundamental roles3. Livestock species and grazing management control soil C and macronutrient inputs, via selective grazing, excreta deposition, and effects on soil exposure and erosion. Models can be applied to understand overall impacts of different livestock management on soil net greenhouse gas exchange4, but require data to reduce uncertainties for intensive grasslands systems. The Centre for International Tropical Agriculture (CIAT) have recently compiled soil and plant biomass data from grassland surveys and experiments carried out since the 1980s, and have requested research collaboration to develop simple models that represent key controls on net emission coefficients. The dataset includes a wide range of soil textures, climatic zones and grazing practices. The project aims to use this resource, together with a systematic review and some empirical work, to develop simple statistical and process models that represent where and how restoration of tropical grasslands can provide net C sequestration. This will contribute to integrated landscape planning. Project descriptionThis project will collate empirical evidence from tropical grasslands of Latin America that identifies under which conditions grasslands become C sinks, and therefore potentially suitable for landscape restoration. The research will combine field level, and mechanistic research with laboratory manipulations to parameterise and test existing soil models. The research will be organised in four phases:1. Literature review and model testing to estimate the size of the effects of soils and grazing management on soil C. The student will conduct a systematic literature review on tropical grasslands, and access an extensive database of experiments at CIAT in Colombia. Results will be used to set up simple ecosystem models such as N14CP5, withholding some datasets for model testing. Statistical analyses will be used to assess major factors and interactions.2. Field work. The student will develop experimental and/or survey designs to fill knowledge gaps that become evident after assessing the existing database. CIAT can offer field sites in the Llanos of Colombia with contrasts in soil texture, depth and organic matter contents, and with seasonal, permanent, and rotational grazing management. The supervision team will assist with experimental design and methods for assessing carbon stocks (to 1 meter depth) and fluxes in vegetation (CO2), and soil (CO2 and CH4). 3. Manipulation experiments. Based on outcomes of the data review and modelling study, the student will select key factors controlling C decomposition such as soil texture, macronutrient inputs (mainly N and P) and water potential, and conduct laboratory incubations aimed at closing remaining knowledge gaps.4. Scenario analyses. The models and relationships developed will be used to assess where net C sequestration can be achieved in degraded land, subject to soil and management constraints.