Field Water Drainage under Traditional and Improved Irrigation Schedules for Corn in Central Spain
Traditional irrigation schedules used by farmers in central Spain may result in overirrigation and deep percolation. The objective of this research was to test whether an improved irrigation schedule based on restoring field capacity in the 0- to 0.5-m soil layer could save irrigation water and reduce drainage (D) without impairing grain yield. A 4-yr field experiment was conducted near Madrid, Spain. A neutron probe and tensiometers were used to measure water in storage and flux in a sandy-loam soil (Typic Xerofluvent) with a corn (Zea mays L.)-wheat (Triticum aestivum L.)-corn-oat (Avena sativa L.) crop rotation common in the area. Crop water consumption and D were estimated with the zero flux plane-water balance equation. The improved irrigation schedule, only applied to the two corn crops, saved 170 mm of irrigation water, or 15% of the irrigation water used for traditionally irrigated plots. Drainage during the experiment was reduced from 235 mm in traditional to 11 9 mm in improved treatment. The cumulative grain yield for subsequent crops was unaffected by the irrigation treatments (31 230 ± 3900 vs. 30 770 ± 3430 kg ha -1 ). Grouped across the 4-yr period, variation of evapotranspiration (ET) between individually instrumented sites (4%) was lower than the variation of D (30%). When daily ET and D estimates were grouped for cropping and intercultivation periods and compared with changes in water storage added to irrigation and rainfall, the mass balance principle was satisfied. Experienced corn farmers may apply this improved schedule by assessing soil depth of wetting.