常规籼稻密度与穴播苗数研究初报

【目的】研究不同栽培密度与穴播苗数对常规籼稻产量的影响,探索出不同穗型品种的合理种植密度和每穴播种苗数以指导农民种植。【方法】采用大穗型常规籼稻材料N2和中穗型常规稻材料N4每667m^2不同栽培密度和穴播种苗数的比较试验。【结果】材料N2在种植密度为1.7万穴/667m^2时产量最高,单产达500.0kg/667m^2,在每穴播种3苗时产量最高,单产达557.6kg/667m^2;材料N4在种植密度2.0万穴/667m^2时产量最高,单产达433.2kg/667m^2,在每穴播种3苗时产量最高,单产达481.1kg/667m^2。【结论】大穗型常规籼稻的最佳栽培方式为种植密度1.7万穴/667m^2与穴播3苗;中穗型常规籼稻的最佳栽培方式为种植密度2.0万穴/667m^2与穴播3苗。

A multigroup model for cholera dynamics and control

We propose a general multigroup model for cholera dynamics that involves both direct and indirect transmission pathways and that incorporates spatial heterogeneity. Under biologically feasible conditions, we show that the basic reproduction number R0 remains a sharp threshold for cholera dynamics in multigroup settings. We verify the analysis by numerical simulation results. We also perform an optimal control study to explore optimal vaccination strategy for cholera outbreaks.