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Soybean Sowing Date: The Vegetative, Reproductive, and Agronomic Impacts

^a Dep. of Agronomy and Horticulture, Univ. of Nebraska, Lincoln, NE 68583-0915
^b Dep. of Agronomy, Iowa State Univ., Ames, IA 50011. Contribution of the Dep. of Agronomy and Horticulture, Univ. of Nebraska, Lincoln, NE 68583. Published as Paper no. 15201, Journal Series Nebraska Agric. Exp. Stn. Project No. 12-194. Funding for this research was received from the Nebraska Agricultural Research Division, Nebraska Soybean Development, Utilization, and Marketing Board, United Soybean Board, and Fluid Fertilizer Foundation

View larger version (148K): [in this window] [in a new window]   Figure 1. Temperature and phenological data for (A) 2003; (B) 2004. Top: Daily (thin line) and 15-d (thick line) mean temperatures from Day 91 to 294 on a day of year (DOY) scale. Middle: Progression of biweekly vegetative node number (Vn) in each planting date. Vn values of –2 and –1 were arbitrarily used to denote the sowing and emergence (VE) stages. Bottom: Progression of biweekly reproductive stage (Rn) number in each planting date. The staging system of Fehr and Caviness (1977) was used. Each V- and R-stage data symbol represents a mean of 140 plants.

View larger version (28K): [in this window] [in a new window]   Figure 2. Fits of a trisegment linear regression model to the triphasic V-stage data shown in Fig. 1 for the four planting dates in 2003 (solid lines) and 2004 (dashed lines). The vertical lines denote the coincident day after planting (DAP) values for V1 and some key R stages. Estimates for all five model parameters and the DAP values for all R stages, are listed in Table 2. The text boxes show the average air temperature (°C) in 2003 (top number) and 2004 (bottom) during the time intervals demarked by the V1, R1, and R5 vertical lines. The horizontal line denotes the stem node number coincident with the peak center parameters of the internode length models (Fig. 4).

View larger version (37K): [in this window] [in a new window]   Figure 3. Mature internode lengths in each of the four planting dates of 2003 and 2004. The beginning (i.e., first) internode, which is located between the cotyledonary node (V0) and unifoliolar node (V1), is symbolized by the leftmost solid-fill section of each bar. Thereafter, alternating open and solid sections of each bar symbolize even- and odd-numbered internodes, whose length in each bar is a mean of two plants, 14 cultivars, and four replicates (i.e., n = 112). For comparability, thin lines connect the same internode across the four planting dates.

View larger version (22K): [in this window] [in a new window]   Figure 4. Lorentzian model fits to the mature internode length data in each of the four planting dates. Estimates and 95% confidence intervals for the three model parameters are depicted in the graph, along with R2 values. For each planting date, the vertical line connects the peak center of amplitude (i.e., longest internode) to its corresponding main stem node number. The horizontal line reflects the peak half-amplitude value, at which the peak half-width (nodal) values apply.

View larger version (22K): [in this window] [in a new window]   Figure 5. Means for planting dates within each year (n = 56 for each symbol) for (A) plant height; (B) plant density at emergence (E) (2004 only) and at maturity (M); (C) seed yield; (D) final 100-seed weight. The best-fitting regression (quadratic or linear) was computed for the four data points of each year, except for 100-seed weight, for which linearity was evident for only three of the four data points each year (see text for further details).