Soil Water Balance

Crop evapotranspiration (ET _c) was calculated using the water balance method by monitoring the change in the soil water content over a period of time. ET _c was estimated using the following water balance equation⁵²:

where ET _c is the crop water consumption (mm); I is the amount of irrigation water (mm); ΔS is the change in soil water storage (mm) before sowing and after harvest, which was measured gravimetrically; the depth interval spacing was 10 cm; R is the run-off (mm); and D is the drainage (mm). There was no precipitation in the greenhouse and no surface runoff from the plots because all furrows were blocked and the surface runoff was negligible; therefore, R = 0. Non-weighting, percolation-type lysimeters (1-mm-thick steel) that were 1.0 m long and 1.2 m wide were installed 0.6 m beneath the bottom of the furrow to collect drainage water. However, no drainage was observed from the lysimeters in each of the plots; thus, D = 0. The overall soil water balance in two consecutive years is shown in Table 3.