Effect of Water Regime and Runoff Strip Width on Soil Water Balance for an Integrated In-Field Rainwater Harvesting

Abstract

Integrating micro-flood irrigation with in-field rainwater harvesting (IRWH) was proposed and experiments were conducted in the 2007–2008 production season at Parady's Experimental Farm of the University of the Free State, South Africa. Three water regimes, dryland (DL), supplemental (SPI), and full irrigation (FI), were tested with 1, 2, and 3 m runoff strip width (RSW) to determine their effects on soil water balance components for the integrated IRWH. Four blocks with nine subplots were prepared for the 3 × 3 split plot factorial experimental design. Plots were 30 m long with a standard 1 m width. Site specific data were used to estimate rainfall-runoff and deep drainage functions. Soil water content (SWC) was measured with a Neutron water meter. Evapo-transpiration (ET) was partitioned into evaporation and transpiration using a β parameter. Deep drainage was the least significantly affected. Rainfalls not less than 24 mm had significantly higher gains on change in SWC for the 2 m and 3 m RSW. During dry spells these RSWs had significantly higher SWC deficit. For the vegetative and reproductive growth stages evaporation from the 3 m RSW constituted not less than 60% of ET compared to less than 40% from 1 m RSW. The 1 m RSW had significantly higher ET and T, irrespective of water regime with the highest values from irrigation treatments. The 1 m RSW can, therefore, be used with either FI or SPI to optimize soil water balance for the integrated IRWH water management.