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Hillslope Variability in Corn Response to Nitrogen Linked to In-Season Soil Moisture Redistribution

^a USDA-ARS, Bldg. 3702, Curtin Rd., University Park, PA 16802
^b Division of Plant Science, Univ. of Missouri, Columbia, MO 65211
^c Dep. of Crop and Soil Sciences, Pennsylvania State Univ., 116 ASI Bldg., University Park, PA 16802

View larger version (18K): [in this window] [in a new window]   Fig. 1. (a) Local relief along a 300-m toposequence, (b) soil water content (0–20 cm), and (c) soil profile water content (0–90 cm) on 30 June, 25 July, and 2 September. Plot locations are identified numerically on the relief diagram (a). Soil water content was determined 5-m downhill from the plot location.

View larger version (19K): [in this window] [in a new window]   Fig. 2. Grain yield response to N fertilizer for all 10 within-field locations and the field-mean yield response for the entire study area (including Location 3). Parameter estimates for regression equations are provided in Table 3. Vertical lines indicate the economic optimum N rate (EONR) for the corresponding regression equation (solid line for Exponential and dashed line for Quadratic-plateau).

View larger version (15K): [in this window] [in a new window]   Fig. 3. Economic optimum N rate (EONR) as a function of grain yield at EONR for nine within-field locations (Location 3 omitted).

View larger version (28K): [in this window] [in a new window]   Fig. 4. (a) Cumulative daily precipitation (1 April–31 October) for 2005; the 30-yr average for State College, PA; mean soil water content (0–20 cm); and mean profile water content (0–90 cm) observed for all 10 locations. (b) Daily precipitation at the study site.

View larger version (17K): [in this window] [in a new window]   Fig. 5. Grain yield at economic optimum N rate (EONR) as a function of the change (25 July–30 June) in soil profile water content (0–90 cm) between 30 June and 25 July.

View larger version (17K): [in this window] [in a new window]   Fig. 6. Economic optimum N rate (EONR) as a function of the change (25 July–30 June) in soil profile water content (0–90 cm) between 30 June and 25 July.