中国农田小麦和玉米产量时空演变及驱动因素

探究中国小麦和玉米产量的时空变化特征和关键驱动因素，为粮食安全战略决策提供理论依据。基于农业农村部近30年（825个点位，1988－2019年）全国农田监测数据，分析了小麦和玉米产量的时空变化特征，利用逐步回归和随机森林模型探究施肥、气候和土壤属性对产量变化的影响，最后通过偏最小二乘法探究各指标影响产量变化的主要调控路径。结果表明，近30年，小麦、玉米单作和二者轮作下平均产量分别为5.05、9.05、6.01和7.08 t/hm2，相应的变异系数为36.6%、26.2%、32.1%和28.0%，相应作物产量随时间的增加速率分别为100、159、46和98 kg/(hm2·a)（P<0.05）。同其他作物轮作下的小麦产量、变异系数和变化速率分别为5.29 t/hm2、28.6%和67 kg/(hm2·a)（P<0.001）。高产玉米主要分布在西北（单作）和华北地区（与小麦轮作）；高产小麦主要分布在同玉米轮作下的长江下游和华北地区。西南地区小麦和玉米产量最低。除了西南和长江中游地区小麦玉米轮作下的小麦产量随监测时间延长呈负增长，其他各区域及全国尺度上的产量均呈正增长。逐步回归结果表明：氮肥对小麦和玉米产量的调控作用均达到极显著水平（P<0.01），而土壤pH的调控作用均未达到极显著水平。针对不同区域而言，随机森林结果显示：除了气候和氮肥的重要性以外，有机质在大部分区域（尤其是西南地区）对产量变化的重要性较大，而钾肥对华北和西北地区的玉米产量变化的重要性较大。通过偏最小二乘法分析发现，土壤属性、肥料投入和气候三者对产量调控的总效应分别为47.6%、29.4%和23.0%，气候主要是通过影响土壤属性和施肥进而调控作物产量。近30年中国小麦和玉米产量整体上呈不断增加趋势，但是西南和长江中游地区小麦玉米轮作下小麦产量随时间呈降低趋势，需引起重视。土壤性质对小麦和玉米产量变化的影响高于施肥和气候，除了氮肥是调控各区域作物产量的关键因素以外，华北、东北和西北地区在种植玉米时还应当重视钾肥合理的投入，而西南地区应当将提升土壤有机质和有效磷含量作为实现高产稳产的主要措施。

Spatio-temporal evolutions and driving factors of wheat and maize yields in China

Explore the spatio-temporal characteristics and key driving factors of wheat and maize yields, and provide a theoretical basis for food security strategic decision-making in the whole country. Based on the national farmland monitoring data of the Ministry of Agriculture and Rural Affairs in the past 30 years (825 points, 1988 to 2019), we analyzed the spatio-temporal variation characteristics of wheat and maize yield. Then we explored the effects of fertilizer application, climate, and soil properties on the yield change by the stepwise regression and random forest model. Finally, partial least squares method was used to explore the main path of each index influencing yield change. In the past 30 years, the average yields wheat and maize under single cropping and rotation system (wheat and maize) were 5.05, 9.05, 6.01, and 7.08 t/hm2, respectively (the latter two were rotation, the same below), with the corresponding coefficient of variations of 36.6%, 26.2%, 32.1%, and 28.0%, and the corresponding increase rates with time were 100, 159, 46, and 98 kg/(hm2·a), respectively (P<0.05). The yield, coefficient of variation and rate of change of wheat in rotation with other crops were 5.29 t/hm2, 28.6%, and 67 kg/(hm2·a) (P<0.001), respectively. The high-yielding areas for maize were mainly distributed in Northwest China (single cropping) and North China (rotation cropping). The high-yielding areas for wheat are mainly in the Lower of Yangtze River and North China (rotation with maize). The lowest yields of wheat and maize were distributed in Southwest China. The relationship between yield and monitoring duration in all regions was generally consistent with the national scale. However, the increased rates of wheat yield under wheat-maize rotation were negative in the Southwest China and Middle of Yangtze River. The results of stepwise regression showed that the nitrogen fertilizer input had a highly significant effect on wheat and maize yield (P<0.01), while the pH not have. For the different regions, the results of random forest showed that in addition to the importance of climate and nitrogen fertilizer, organic matter played a relatively strong role in regulating yield in most regions (especially in Southwest China), while potassium fertilizer played a relatively strong role in regulating maize yield in North and Northwest China. Partial least squares analysis showed that the total effects of soil properties, fertilizer input and climate on crop yield were 47.6%, 29.4%, and 23.0% respectively. Climate mainly regulated crop yield by affecting soil properties and fertilizer input. Wheat and maize yields have been increasing overall in China from 1988 to 2019, while the wheat yield under rotation cropping system in Southwest China and the lower reaches of the Yangtze River has been decreasing with time. The yield of wheat and maize is more regulated by soil properties than by fertilization and climate. Nitrogen fertilizer is the key factor to ensure the high yield in each region. In addition, the potassium fertilizer reasonable application should be paid more attention at maize season to ensure high and stable yields in North China, Northeast and Northwest China. The improvement of soil organic matter and available phosphorous should be as the main measures to achieve high and stable yields in Southwest China.