Zhang, Y., Feng, L., Wang, E., Wang, J. and Li, B. 2012. Evaluation of the APSIM-Wheat model in terms of different cultivars, management regimes and environmental conditions. Can. J. Plant Sci. 92: 937–949. Wheat is one of the most important crops in the world, and wheat models have been widely used to study yield responses to changes in management and climate. However, less information is available on how a wheat model performs in simulation of wheat response to changes in varieties, sowing dates and planting densities across space. This study presents an evaluation of the APSIM-Wheat model using data from field experiments consisting of three sowing dates, two and three crop varieties and three planting densities in a split-split plot design at three ecological sites from 2008 to 2010 in the North China Plain. The results show that the APSIM-Wheat model could capture a large part of the variation in phenology, biomass and yield for the same variety across sites. However, errors of simulation in phenology and yield were increased with delay in sowing date, with the average absolute root mean square errors of 2 d, 3 d, and 3–4 d in phenology, and the normalized root mean square error (RMSEn) of 7–12%, 11–16%, 16–22% in yield at early, medium, and late sowing dates, respectively. Simulation of yield achieved poor results with decreased planting density, with average RMSEn of 9–12%, 11–12%, and 16–19% at high, medium, and low density, respectively. Additionally, the simulation behaved in a complex manner, and the errors varied greatly with different combinations of sowing dates and planting densities. These alerted us that the model should be used cautiously to simulate growth and yield over a wide range of sowing dates and planting densities. Improved modeling of the responses of wheat growth to extreme temperatures during winter and spring periods, and to varying planting densities is needed for better future prediction. Other areas of model improvements are also discussed.
L. 2015. The effects of different water and nitrogen levels on yield, water and nitrogen utilization efficiencies of spinach (Spinacia oleracea L.). Can. J. Plant Sci. 95: 671Á679. Water and nitrogen (N) are important factors that affect crop yield. The objective of this study was to explore the interactive effect of water and nitrogen on biomass production, yield and growth responses, water and nitrogen use efficiency of winter-grown spinach. A field experiment was grown with treatments of varying water (W) and nitrogen (N) levels near Shanghai, China. Leaf area, shoot biomass and height of spinach increased with the application of N in the well-watered treatment. The highest chlorophyll content was found in spinach treated with N 2 (170 kg ha(1 nitrogen). A response surface analysis was done on plant height, leaf number, leaf weight, and plant yield of each spinach plant at different water and nitrogen levels. The equation for each of the response surfaces was taken and solved for the mathematical optimum of the curves. Abundant water supply resulted in the highest spinach yield. Yield of spinach increased with N application rates but decreased when the N was excessive. Compared with the low water treatment (W 3 ), a higher N leaching ratio was observed in the high water treatment (W 1 ), regardless of N treatment. With the increase of N application, N use efficiency of spinach significantly decreased, while water use efficiency of spinach increased. In conclusion, water levels between 36.15 cm and 42 cm, and nitrogen applications between 86 and 152.74 kg ha(1 could be recommended as the optimal treatment for spinach growth.
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