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Impact of Within-Field Variability in Soil Hydraulic Properties on Transpiration Fluxes and Crop Yields

A Numerical Study

^a Université Catholique de Louvain, Department of Environmental Sciences and Land Use Planning, Croix du Sud 2, BP 2, B-1348 Louvain-la-Neuve, Belgium
^b Wageningen Agricultural University, Department of Environmental Sciences, Nieuwe Kanaal 11, 6709 PA Wageningen, The Netherlands

View larger version (14K): [in a new window]   Fig. 1. Schematic of the adjustment procedure for the critical pressure head h3h. Figure 1a shows the reference moisture retention curve ( = 0.0051) and that of a similar soil with = 0.002. Figure 1b presents the two corresponding hydraulic conductivity curves and the K3ref value used for the adjustment.

View larger version (17K): [in a new window]   Fig. 2. Impact of perturbations in and n on the actual cumulative transpiration rate (Fig. 2a) and on crop yield (Fig. 2b) for the dry 1990 climatic scenario.

View larger version (31K): [in a new window]   Fig. 3. (a–c) The measured spatial variability in the moisture retention curves (MRC) for the first (45 cm), second (75 cm), and third (105 cm) depths, respectively; (d) the 28 MRCs with soil hydraulic properties averaged for the three investigated depths.

View larger version (22K): [in a new window]   Fig. 4. Impact of the within-field variability in soil hydraulic properties on (c, d) the actual transpiration rate and (e, f) the dry matter yield for the relatively (a, c, e) dry 1990 and (b, d, f) wet 1998 climatic scenarios. Whiskers indicate the maximum and minimum simulated values. (a, b) Rainfall rates for the two climatic scenarios.

View larger version (24K): [in a new window]   Fig. 5. Comparison between simulated and measured soil water contents for the 1999 climatic scenario for the different depths: (a) 0–20 cm, (b) 25 cm, (c) 50 cm, and (d) 75 cm. Dots indicate the average of the field measured soil water contents, continuous and dotted lines the mean and the extremes of the 1120 simulated soil water contents, respectively.

View larger version (19K): [in a new window]   Fig. 6. Scatter plots of the adjusted critical pressure heads h3l and h3h. Arrows indicate reference values of –325 and –600 cm for h7h and h3l, respectively.

View larger version (40K): [in a new window]   Fig. 7. Two-dimensional response surfaces of objective functions (OFs) obtained when h4 is simultaneously optimized with (a, b, e, f) n and (c, d, g, h) for the (a–d) 1990 and (e–h) 1998 agricultural seasons. The left (a, c, e, g) and the right figures (b, d, f, h) show OF response surfaces calculated using actual cumulative transpiration rates and final dry matter yields, respectively.