Application of the Hybrid-Maize model for limits to maize productivity analysis in a semiarid environment

Effects of meteorological variables on crop production can be evaluated using various models. We have evaluated the ability of the Hybrid-Maize model to simulate growth, development and grain yield of maize (Zea mays L.) cultivated on the Loess Plateau, China, and applied it to assess effects of meteorological variations on the performance of maize under rain-fed and irrigated conditions. The model was calibrated and evaluated with data obtained from field experiments performed in 2007 and 2008, then applied to yield determinants using daily weather data for 2005-2009, in simulations under both rain-fed and irrigated conditions. The model accurately simulated Leaf Area Index , biomass, and soil water data from the field experiments in both years, with normalized percentage root mean square errors < 25 %. Gr.Y and yield components were also accurately simulated, with prediction deviations ranging from -2.3 % to 22.0 % for both years. According to the simulations, the maize potential productivity averaged 9.7 t ha-1 under rain-fed conditions and 11.53 t ha-1 under irrigated conditions, and the average rain-fed yield was 1.83 t ha-1 less than the average potential yield with irrigation. Soil moisture status analysis demonstrated that substantial potential yield may have been lost due to water stress under rain-fed conditions

The effect of sowing date on infection of sugar beet by Polymyxa betae

The effect of sowing date on the infection of sugar-beet seedlings by Polymyxa betae was examined in a small-plot experiment on a naturally infested site. Seed was sown on seven occasions at weekly intervals from late March to early May. From each sowing, plant samples were taken at approximately weekly intervals over a period of 7 weeks. The extent of root infection by P. betae and the dry weight of plants was determined at each sampling date, and the progress of infection and rate of plant growth were examined against time and thermal time. Infection occurred sooner after sowing and the subsequent rate of fungal development was more rapid in late-sown than in early-sown plants. Early sowing allowed germination and growth of sugar beet at temperatures too low for fungal infection. The growth of late-sown plants appeared to be reduced by P. betae infection. The implications of these findings for the development of rhizomania disease are discussed