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Estimating Grain and Straw Nitrogen Concentration in Grain Crops Based on Aboveground Nitrogen Concentration and Harvest Index

^a Biological Systems Engineering Dep., Washington State Univ., Pullman, WA 99164-6120 (current address: Texas Agricultural Experiment Station, Blackland Research and Extension Center, Temple, TX 76502)
^b Biological Systems Engineering Dep., Washington State Univ., Pullman, WA 99164-6120
^c USDA-ARS, Washington State Univ., Pullman, WA 99164-6421

View larger version (29K): [in this window] [in a new window]   Fig. 1. Calibration of the parameter C for wheat, barley, maize, and sorghum. For wheat and barley, the data are from Pullman, WA; for maize, data are from 1 yr from Derby et al. (2005) and from Huggins et al. (2001); for sorghum, data are from Kamoshita et al. (1998a). Wheat average harvest index (HI) and aboveground nitrogen concentration (Nt) were 0.42 (range 0.30–0.56) and 11.5 (range 8.1–16.7 g kg–1); barley average HI and Nt were 0.43 (range 0.35–0.53) and 9.6 (range 6–15.3 g kg–1); maize average HI and Nt were 0.55 (range 0.36–0.68) and 8.3 (range 5.1–10.8 g kg–1); sorghum average HI and Nt were 0.37 (range 0.18–0.48) and 10.4 (range 6.3–15.8 g kg–1). RMSE and MAD are RMSE and mean absolute difference between observed and predicted Ng.

View larger version (34K): [in this window] [in a new window]   Fig. 2. Testing of the model for wheat. Fischer (1993), Olesen et al. (2000), and Wuest and Cassman (1992) treatments were nitrogen (N) fertilization rate and timing in irrigated experiments. Olesen et al. (2000) experiments were affected by powdery mildew and Septoria spp. McDonald (1992) treatments were N fertilization rates and site. Halvorson et al. (2004) treatments were fertilization rate, rotation, and year in dryland winter wheat in Akron, CO. Huggins (1991) treatments were N fertilization rates and timing in dryland spring wheat in a Mediterranean climate (Pullman, WA).

View larger version (17K): [in this window] [in a new window]   Fig. 3. Testing of the model for barley, maize, and sorghum. The data for spring barley are from Pullman, WA (Huggins, unpublished) and from Bulman and Smith (1993b) in an experiment in Canada; their data is the average of three cultivars. Data from Delogu et al. (1998) are for winter barley growing at three nitrogen (N) fertilization rates (0, 80, and 140 kg N ha–1); each point is the average of 2 yr. Data for maize are from Bodley (2004) and Derby et al. (2005) for maize grown at different N fertilization rates in Pullman, WA and Oakes, ND, respectively. Data from Mehdi et al. (1999) correspond to 2 yr and different tillage practices. The data for sorghum from Kamoshita et al. (1998b) are from three hybrids grown at 0 and 240 kg N ha–1, and data from Traore and Maranville (1999) are for different genotypes adapted to the experimental area (Nebraska) or adapted to tropical growing conditions.

View larger version (21K): [in this window] [in a new window]   Fig. 4. Modeled variation of the grain nitrogen (N) concentration in response to aboveground biomass N concentration at harvest and to the harvest index using the parameters fitted for wheat and maize.