WATER AND SOLUTE MOVEMENT UNDER CONVENTIONAL CORN IN CENTRAL SPAIN .1. WATER-BALANCE

Partitioning temporal changes in soil water storage to water balance c omponents (evapotranspiration [ET], drainage) under field conditions r emains a vexing task. An in situ protocol using neutron probes and ten siometers was established on a sandy loam (Typic Xerofluvent) under ir rigated, conventional corn (Zea mays L.) with the objectives to separa te ET from deep drainage and to improve the accuracy of estimating the water balance components. An experimental research site (0.4 ha) at L a Poveda Field Station near Madrid (Spain) was divided into 24 plots o f 9 by 11.1 m each. The heterogeneity of the research site had been pr eviously determined and the experimental held was instrumented accordi ngly. Vacuum soil-water extractors were placed in all plots, but neutr on probe and tensiometers were installed in only eight plots based on soil texture. Plot management included nine furrow irrigations of 404 mm and rainfall of 250 mm throughout the growing season. Measurements of water flow and soil water storage for periods of a few days allowed the determination of ET and drainage with the soil water balance equa tion. Four water flow patterns and six water balance cases were identi fied. Results showed a cumulative ET of 532 +/- 70 mm and total draina ge of 75 +/- 22 mm below the 1.4-m soil depth. Peak drainage took plac e 20 d before maximum ET and represented 19% of total irrigation water .