Effects of land use intensification and soil management practices on field water cycles and water use efficiency

在班加罗尔的城乡结合部，水对农作物生产的影响越来越有限。土地利用的集约化、土壤管理方法的转变和城市化推动的用水增加预计将对已经稀缺的水资源施加额外的压力。通过对需水作物（如蔬菜、葡萄）实施高效灌溉系统或优化土壤保持水分管理方法（如覆盖、腐殖质管理、提高水利用效率）的节水战略将是维持该地区未来作物生产的关键因素。本项目旨在探讨城市化进程中农业转型对农田水循环的影响。我们将沿着一条代表从农村向城市地区过渡的样带（简称“城乡界面”，RUI），分析土地利用集约化过程中土壤的水力和物理功能的变化。物理土壤特性将通过实验室方法确定，使用具有代表性的未受干扰的土壤样品和在现场（例如渗透性，土壤水分动态，剪切强度和渗透仪阻力）。调查将在UAS/Bangalore实验站进行(i)在研究者管理的条件下（包括灌溉、氮水平和作物轮作因素）的现场进行；（ii）在沿着城乡梯度的选定农场，由农民管理的农场采用两种水管理水平（雨养与灌溉）结合两种作物多样性水平（单一栽培与复合栽培）。农场现场分析将在一年中的几个时间在嵌套网格中进行，以便使用地质统计学方法得出农场尺度土壤性质的时空分布。为了计算田间水分平衡、各种处理（如施氮、灌溉、作物多样性）的水分和雨水利用效率，我们将结合实验室和田间的土壤物理测量参数化一个确定性运输模型（HYDRUS）。该模型将根据安装在无人机站内实验点的监测剖面获得的土壤湿度和温度的原位数据进行校准和验证。经过验证的模型提供了一种基于物理的工具来预测SPAC的土壤水分有效性和通量，并可能与作物模拟模型相结合，以评估不同管理和气候情景下的作物表现。

In the rural-urban interface of Bangalore water is an increasingly limited factor in crop production. Intensification of land use, transitions in soil management practices and the urbanization driven increase in water use are expected to exert additional pressure on the already scarce water resources. Water saving strategies by implementing efficient irrigation systems for water demanding crops (e.g. vegetables, grapes) or optimizing soil moisture conserving management approaches (e.g. mulching, humus management, increase in water use efficiency) will be crucial factors for sustaining future crop production in this region. This project aims at investigating the effects of agricultural transformation in the course of urbanization on the field water cycle. We will analyze changes in hydraulic and physical soil functions with land use intensification along a transect representing the transition from rural to urban areas (short rural-urban interface, RUI). Physical soil properties will be determined both by lab methods using representative undisturbed soil samples and in the field (e.g. infiltrability, soil moisture dynamics, shear strength and penetrometer resistance). Investigations will be carried out (i) on-station under researcher managed conditions (with factors irrigation, N-level and crop rotation) at the experimental station at UAS/Bangalore and (ii) on-farm managed by farmers with two levels of water management (rainfed vs. irrigated) combined with two levels of crop diversity (monoculture vs. polyculture) at selected farms along the urban-rural gradient. On-farm field analysis will be done in nested grids at several times of the year in order to derive farm scale spatial and temporal distribution of soil properties using geostatistical approaches. To calculate field water balances, water and rain use efficiencies for the various treatments (e.g. N application, irrigation, crop diversity) we will parameterize a deterministic transport model (HYDRUS) combining the soil physical measurements from the lab and the field. The model will be calibrated and validated based on in situ data of soil moisture and temperature which are obtained by monitoring profiles installed at the on-station experimental sites of the UAS. The validated model provides a physically based tool to predict soil water availability and fluxes in the SPAC and can potentially be coupled with crop simulation models to assess crop performance under varying management and climate scenarios.