Climate suitability grading and planting zoning of soybean in Northeast Inner Mongolia

In northeast of Inner Mongolia, soybean production is faced with two problems. The first is that soybean planting area is zoned with ≥ 10℃ accumulative temperature without non clear division between soybean and maize region. The second is the use efficiencies of heat and water in the area are low in the area. In order to efficiently make use of water and heat resources in soybean cultivation and promote soybean production in cool area, we used meteorological observation data and soybean crop growing phrases data in years from 1987 to 2016 in Hulun Buir, Xing'an League in Northeast Inner Mongolia, and surrounding areas in Heilongjiang Province to analyze the climate suitability of soybean in Hulun Buir. In the study, temperature suitability, precipitation suitability of soybean were calculated, respectively, with the "three basis points" of temperature and water demand in each growth phase of soybean, while the climate suitability was calculated with the comprehensive hydrothermal suitability model. Furthermore, planting zoning of soybean cultivation in Hulun Buir was conducted according the comprehensive hydrothermal suitability level in GIS environment. The results showed that for the temperature suitability and comprehensive hydrothermal suitability, ≥ 0.6, 0.4-0.6 and ≤ 0.4 were classified as most suitable, more suitable and unsuitable. For precipitation suitability, ≥ 0.7 was most suitable, 0.6-0.7 more suitable and ≤ 0.6 unsuitable. The most suitable areas for planting soybean were in the southeast of Daxing'anling farming region, more suitable areas at the edge of the planting region in eastern Daxing'anling, then unsuitable areas were in the north woodland and western pastoral of Hulun Buir. Agroforestry ecotone in the south of forest region where accumulated temperature exceeded 10℃ was 1 900-2 100℃, which was not suitable for cultivating corn, but could be developed vigorously for cultivating soybean. This area was considered for increased soybean acreage during structural crop adjustment. The results provided reference for soybean production in the cool area in Northeast China.