Shallow groundwater affects terrestrial ecosystems by sustaining river base-flow and root-zone soil water in the absence of rain, but little is known about the global patterns of water table depth and where it provides vital support for land ecosystems We present global observations of water table depth compiled from government archives and literature, and fill in data gaps and infer patterns and processes using a groundwater model forced by modern climate, terrain, and sea level Patterns in water table depth explain patterns in wetlands at the global scale and vegetation gradients at regional and local scales Overall, shallow groundwater influences 22 to 32% of global land area, including ~15% as groundwater-fed surface water features and 7 to 17% with the water table or its capillary fringe within plant rooting depths

http://science.sciencemag.org/content/sci/339/6122/940.full.pdf

Global patterns of groundwater table depth.

Increasing the productivity of the rice–wheat (RW) system in north-west India is critical for the food security of India. However, yields are stagnating or declining, and the rate of groundwater use is not sustainable.

Many improved technologies are under development for RW systems, with multiple objectives including increased production, improved soil fertility, greater input use efficiency, reduced environmental pollution, and higher profitability for farmers. There are large reductions in irrigation amount with many of these technologies compared with conventional practice, such as laser land leveling, alternate wetting and drying (AWD) water management in rice, delayed rice transplanting, shorter duration rice varieties, zero till wheat, raised beds, and replacing rice with other crops. However, the nature of the irrigation water savings has seldom been determined. It is often likely to be due to reduced deep drainage, with little effect on evapotranspiration (ET).

Reducing deep drainage has major benefits, including reduced energy consumption to pump groundwater, nutrient loss by leaching, and groundwater pollution. The impacts of alternative technologies on deep drainage (and thus on irrigation water savings) vary greatly depending on site conditions, especially soil permeability, depth to the watertable, and water management. More than 90% of the major RW areas in north-west India are irrigated using groundwater. Here, reducing deep drainage will not “save water” nor reduce the rate of decline of the watertable. In these regions, it is critical that technologies that decrease ET and increase the amount of crop produced per amount of water lost as ET (i.e., crop water productivity, WPET) are implemented. The best technologies for achieving this are delaying rice transplanting and short duration rice varieties. The potential for replacing rice with other crops with lower ET is less clear.

Halting the groundwater decline in north-west India--which crop technologies will be winners?

Effects of salt and waterlogging stresses and their combination on leaf photosynthesis, chloroplast ATP synthesis, and antioxidant capacity in wheat.

Subsurface drainage to combat waterlogging and salinity in irrigated lands in India: Lessons learned in farmers’ fields

Effect of drip irrigation on yield of cabbage (Brassica oleracea L. var. capitata) under mulch and non-mulch conditions

Effect of drip irrigation and mulching on tomato yield

/pdf/drainage-protects-irrigation-investments-27u4q85xyr.pdf

Drainage protects irrigation investments

Three years pooled results showed that drip irrigation, in general, increased banana yield as compared to surface method along with water saving of 30%, 43% and 56% in 0.45, 0.60 and 0.75 FPE (Fraction of Pan Evaporation) respectively. It was observed that while drip alone could save water considerably without any reduction in banana production, drip coupled with mulches could simultaneously increase the crop yield in addition to water savings. Between the two mulches sugarcane trash mulch was found better than black plastic. The maximum yield (66 t/ha) was recorded in the treatment of drip with SM at 0.75 (FPE), which did not differ significantly from 0.60 FPE of the same combination, but significantly better than 0.45 FPE. The net income indicated that all drip treatments either alone or in combination with mulches, except 0.60 and 0.75 FPE of SM (Sugarcane trash Mulch) resulted in lower return than surface method. But drip alone at 0.75 FPE resulted in almost same return as the surface method along with 30% water saving. However by covering an additional area through the saved water gross income could be increased (doubled in DSM0.60 (Drip + Sugarcane trash Mulch + 0.60 FPE) as compared to control.

S. Raman

Papers

Subsurface drainage to combat waterlogging and salinity in irrigated lands in India: Lessons learned in farmers’ fields

Effect of drip irrigation and mulching on tomato yield

Drainage protects irrigation investments

Response of banana to drip irrigation, mulches and irrigation scheduling in South Gujarat