A02: Effects of soil and land management on the water cycle in the soil and watershed.

Project A02 investigates the influence of soil- and crop management on the water balance in the peri-urban and rural areas of Bengaluru. Thus, the sampling of the field experimental plots of the first phase for physical soil properties will be continued in order to detect long-term changes. A spatial and temporal analysis of soil moisture and plant water stress will be compared with crop yields of projects A01 and C01 for a detection of the influence of water availability on plant growth. Aggregate stability will be investigated as a proxy for infiltration-reducing physical soil crusts. This will enable an estimation of infiltration behaviour depending on soil management during the Monsoon period. Socio-hydrological scenarios and feedbacks for an estimation of the effects of alternative soil and crop management scenarios on the water balance at field and catchment scale will be defined using existing data (panel survey data (projects B02 and C05, phase I), land use classifications, soil crusting (this project), the literature). The feedbacks will be used to define an agent-based model, which will be coupled to the catchment scale hydrological model SWAT. The coupled model and an existing field-scale model (HYDRUS) will be used for the scenario-simulation. Scenario results will be jointly discussed at both scales in order to gain knowledge about changes in the water cycle at field and catchment scale and in order to learn how both scales can inform each other. In the third phase, the water balance of lakes and tanks used for irrigation will be investigated in order to learn about the efficiency of water storage and about the water and solute pathways in and around these tanks. The solute transport (nitrogen, heavy metals, pesticides) of irrigation water in the unsaturated soil zone will be simulated for an estimation of the fate of these substances.

Prof. Dr. S. Peth
Soil Sciences
University of Hannover

Prof. Dr. M. Gaßmann
Hydrology and Matter Cycles
University of Kassel

Albara Almawazreh 
Doctoral Researcher

Tejas Kulkarni 
Doctoral Researcher

Indian Partner-Project:
Effects of agricultural water and nutrient management on farmers livelihoods
A. Sathish, University of Agricultural Sciences, Bangalore

Effects of land use intensification on field water cycles and water use efficiency

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. Main focus will be on modifications of (i) water holding and infiltration capacities, (ii) least limiting water ranges (LLWR) and (iii) water use efficiencies (WUE) of rainfed and irrigated systems as well as on (iv) overall soil physical quality. Currently there is not much information on how land use intensification and adaption to changes associated with urbanization in the agricultural ecosystem of Bangalore region will influence physical soil properties which determine water availability and fluxes in the soil-plant-atmosphere continuum (SPAC) on the farm scale. Systematic investigations on soil water characteristics, hydraulic functions and moisture dependent mechanical soil impedance restricting root growth and hence water uptake are widely lacking.

We will analyse changes with land use intensification of soil hydraulic (transport functions, water release curves, soil water storage), soil mechanical (shear strength, penetration resistances, aggregate stability) and soil thermal (soil temperature and heat fluxes) parameters. 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 versus irrigated) combined with two levels of crop diversity (monoculture versus polyculture) at selected farms along the rural-urban 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.

Sybille Lehmann
Doctoral Researcher