Water fluxes at a fluctuating water table and groundwater contributions to wheat water use in the lower Yellow River flood plain,China

Capillary upflow from and deep percolation to a water table may be important in crop water supply in irrigated areas of the lower Yellow River flood plain, north China. These fluxes at the water table and the variations of the capillary upflow in relation to crop evapotranspiration need to be investigated to quantify the effect of a water table on soil water balance and to improve agricultural water management. A large weighing lysimeter was used to determine daily crop evapotranspiration, daily capillary upflow from and daily percolation to a fluctuating water table during a rotation period with wheat growing in a dry season and maize in a rainy season. The water table depth varied in the range 0·7–2·3 m during the maize growth period and 1·6–2·4 m during the wheat growth period. Experimental results showed that the capillary upflow and the percolation were significant components of the soil water balance. Three distinctly different phases for the water fluxes at the water table were observed through the rotation period: water downward period, the period of no or small water fluxes, and water upward period. It implied that the temporal pattern of these water fluxes at the water table was intimately associated with the temporal distribution of rainfall through the rotation period. An empirical equation was determined to estimate the capillary upflow in relation to wheat evapotranspiration and root zone soil water content for local irrigation scheduling. Coupled with the FAO‐Penman–Monteith equation, the equation offers a fast and low cost solution to assess the effect of capillary upflow from a water table on wheat water use. Copyright © 2007 John Wiley & Sons, Ltd.