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Nitrate Exported in Drainage Waters of Two Sprinkler-Irrigated Watersheds

^a Dep. Genética y Producción Vegetal, Estación Experimental de Aula Dei (CSIC), and Laboratorio de Agronomía y Medio Ambiente (DGA-CSIC), Apdo. 202, 50080 Zaragoza, Spain
^b Dirección General de Estructuras Agrarias (DGA), P. M^a Agustín 36, 50004 Zaragoza, Spain
^c Unidad de Suelos y Riegos, Servicio de Investigación Agroalimentaria (DGA), and Laboratorio de Agronomía y Medio Ambiente (DGA-CSIC), Apdo. 727, 50080 Zaragoza, Spain

View larger version (39K): [in a new window]   Fig. 1. Schematic layout of Watersheds A and B with indication of the hydrological limits, the main and secondary drainage collectors, the irrigated fields, and the location of the weather station and the gauging stations.

View larger version (51K): [in a new window]   Fig. 2. Irrigation performance index [IPI = (NIR/Viw) x 100, where NIR is net irrigation requirement and Viw is the volume of irrigation water] for the 1997 and 1998 irrigated months and the 1997 and 1998 irrigated seasons in Watersheds A and B.

View larger version (27K): [in a new window]   Fig. 3. Relationships and linear regression equations between the weekly irrigation performance index (IPI) values and the weekly volumes of effective precipitation (Peff) in Watershed A (1997 and 1998 irrigation season) and Watershed B (1998 irrigation season).

View larger version (29K): [in a new window]   Fig. 4. Relationships between maize grain yield and (A) available N and (B) percent of total N applied at maize preplanting.

View larger version (39K): [in a new window]   Fig. 5. Relationships between maize grain N (A and E), stalk N (B and F), stalk NO3–N (C and G), and soil NO3–N (D and H), and total and postplant applied fertilizer N measured in 1998 at 10 maize fields of Watershed A at harvest. Each point is the mean ± standard deviation of four sampling locations within each field.

View larger version (44K): [in a new window]   Fig. 6. Weekly values of drainage flow (A), irrigation and precipitation (B), NO3–N concentration in drainage water (C), and NO3–N load in drainage water (D) in the study periods April 1997 through March 1999 (Watershed A) and October 1997 through September 1998 (Watershed B). The scale for drainage flow is double the scales for irrigation and precipitation.