DSSAT Maize simulated sowing dates for Nigeria for the period, 1981-2019

Climate change and inter-annual variability cause variation in rainfall commencement and cessation which has consequences for the maize growing season length and thus impact yields. This study therefore sought to determine the spatially explicit optimum maize sowing dates to enable site specific recommendations in Nigeria. Gridded weather and soil data, crop management and cultivar were used to simulate maize yield from 1981-2019 at a scale of 0.5°. A total of 37 potential sowing dates between 1 March and 7 November at an interval of 7 days for each year were evaluated. The optimum sowing date was the date which maximizes yield at harvest, keeping all other management factors constant. The results show that optimum sowing dates significantly vary across the country with northern Nigeria having notably delayed sowing dates compared to southern Nigeria which has earlier planting dates. The long-term optimal sowing dates significantly (p<0.05) shifted between the 1980s (1981-1990) and current (2011-2019) for most of the country. The most optimum planting dates of southern Nigeria shifted to later sowing dates while most optimum sowing dates of central and northern Nigeria shifted to earlier sowing dates. There was more variation in optimum sowing dates in the wetter than the drier agro-ecologies. Changes in climate explain changes in sowing dates in wetter agro-ecologies compared to drier agro-ecologies. The study concludes that the optimum sowing dates derived from this study and the corresponding methodology used to generate them can be used to improve cropping calendars in maize farming in Nigeria.

气候变化与年际变率会引发降雨起止时间的波动，进而影响玉米生育期长度，最终对产量造成不利影响。因此本研究旨在确定空间显式（spatially explicit）的最优玉米播种日期，以期为尼日利亚提供因地制宜的种植建议。本研究采用网格气象与土壤数据、作物管理措施及品种参数，在0.5°分辨率下模拟了1981-2019年的玉米产量。每年评估3月1日至11月7日之间、间隔7天的共计37个潜在播种日期。最优播种日期定义为在其他管理因素保持不变的前提下，能使收获时产量达到最大值的日期。研究结果表明，尼日利亚全国的最优播种日期存在显著空间异质性：南部地区适宜较早播种，而北部地区的最优播期则显著偏晚。全国大部分区域的长期最优播种日期在1980年代（1981-1990年）与当前时期（2011-2019年）之间发生了显著变化（p<0.05）。其中，尼日利亚南部地区的最优播种日期显著延后，而中部与北部地区的最优播期则显著提前。相较于较干旱的农业生态区（agro-ecologies），湿润农业生态区内的最优播种日期波动幅度更大。相较于干旱农业生态区（agro-ecologies），气候变化可更好地解释湿润农业生态区内播种日期的变化。本研究结论指出，本研究得到的最优播种日期及其对应的生成方法，可用于优化尼日利亚玉米种植的种植历。