China's Wheat Planting Regions and the Growing Conditions of Each Region
Wheat is widely distributed in China and is grown all over the country. Because natural conditions vary from place to place, distinctly different growing regions have formed. As early as 1936, China's wheat was divided into 7 regions based on climate and wheat production conditions, of which 6 were winter wheat regions and 1 was a spring wheat region; in 1937, based on the results of 3-year regional adaptability trials of more than 100 wheat varieties at 9 locations in 8 provinces, the 6 winter wheat regions were grouped into 3 main regions. This was the earliest study on wheat regionalization in China.
In 1943, based on the winter or spring habit of Chinese wheat, grain color, and hardness or softness of texture, the main wheat regions nationwide were divided into 3 growing regions: the hard red spring wheat region, the hard winter-spring wheat mixed region, and the soft red winter wheat region. In the early 1960s, "Chinese Wheat Cultivation" again divided the country's wheat into 3 main regions and 10 subregions: the northern winter wheat region, the southern winter wheat region, and the spring wheat region, laying the foundation for a relatively complete wheat regionalization of China. In particular, the boundary line between winter and spring wheat and the division of each major wheat region were redefined. Later, scientific researchers in meteorology, variety science, cultivation, and other disciplines successively proposed different regionalizations according to the characteristics of their respective disciplines. Based on the regionalization in "Chinese Wheat Cultivation," the book "Chinese Wheat Varieties and Their Pedigrees" directly divided the country into 10 wheat regions, and some regions were further divided into several subregions.
Since the 1980s, wheat production across the country has developed rapidly, relevant materials on wheat regionalization have been continuously enriched, and understanding has continued to deepen. For this reason, on the basis of the original 10 wheat regions - Northeast spring wheat, Northern spring wheat, Northwest spring wheat, Xinjiang winter-spring wheat, Qinghai-Tibet spring-winter wheat, Northern winter wheat, Huang-Huai winter wheat, Middle and Lower Yangtze winter wheat, Southwest winter wheat, and South China winter wheat - the national wheat planting regionalization focused on making corresponding revisions and adjustments to the scope of each region and the direction of the regional boundaries. According to the different natural conditions and wheat cultivation characteristics across China, the country is divided into different types of wheat growing regions, so as to facilitate adapting measures to local conditions and rationally arranging wheat production.
1. Northeast Spring Wheat Region
The Northeast Spring Wheat Region includes all of Heilongjiang and Jilin provinces, most of Liaoning Province except the southern coastal area, and the northeastern part of the Inner Mongolia Autonomous Region. The wheat area and total output of the entire region are each about 8% of the national totals, and account for about 47% and 50% of the national spring wheat area and total output, respectively, so it is the main spring wheat producing area, with Heilongjiang Province predominant.
The Northeast Spring Wheat Region is high in the northwest and low in the southeast; in most areas the altitude is 40-500 m, and in parts of Inner Mongolia in the northwest it can reach 600-800 m. The soil is mainly chernozem, with deep soil layers and fertile texture. In the Sanjiang Plain of eastern Heilongjiang and the Heihe area of northern Heilongjiang, wheat area is relatively concentrated, and large numbers of state farms have been established; their wheat output accounts for about 1/2 of the total spring wheat output of Heilongjiang Province. The entire region has a continental climate, with low temperatures and insufficient heat, and extremely large differences between winter and summer temperatures. Temperature increases from north to south; the average temperature of the coldest month is -23 to 10°C, and the absolute minimum temperature is -41 to 27°C, making it the lowest-temperature region in the country. Annual precipitation is 320-870 mm, and precipitation during the wheat growing period is 130-333 mm, but the east is rainy and the west is dry. In the Sanjiang Plain of eastern Heilongjiang, excessive rain in the later period often causes wet waterlogging disasters and affects harvest. In contrast, areas such as Baicheng in Jilin Province and Chaoyang in Liaoning Province in the west often suffer from drought and wind-sand damage because of spring drought and strong winds. Wheat varieties in this region are spring type, sensitive to photoperiod response, and have a short growing period, mostly around 90 days. Diseases are mainly root rot, rust, and fusarium head blight, while dwarf mosaic and take-all also occur. The cropping system is one crop per year; sowing is in mid-April and maturity is around July 20. In the entire region, in addition to timely control of various diseases, draining water and preventing wet damage in the east; controlling weeds in the north; and in the west building water conservancy facilities and adopting cultivation techniques such as less deep plowing, more deep loosening, and reduced tillage or no-tillage to prevent wind and fix sand and reduce evaporation are all main measures for increasing wheat yield. According to the distribution of temperature and precipitation, this region can further be divided into 3 subregions: the northern high-cold subregion, the eastern humid subregion, and the western arid subregion.
2. Northern Spring Wheat Region
The Northern Spring Wheat Region is located west of the Greater Khingan Mountains, north of the Great Wall, west to the Ih Ju League and Bayannur League of the Inner Mongolia Autonomous Region, and borders the People's Republic of Mongolia to the north. The entire region is mainly Inner Mongolia Autonomous Region, and also includes areas north of the Great Wall in Hebei and Shaanxi provinces and northern Shanxi Province. The wheat planting area and total output of the entire region account for about 3% and 1% of the national totals, respectively, and about 20% of the region's grain crop area. The average wheat yield per unit area is the lowest among all wheat regions in the country, and development is very uneven; the yield level is relatively high in the Ih Ju League and Bayannur League of the western Hetao Irrigation District, while Zhangjiakou in Hebei Province, Yanbei in Shanxi Province, and Yulin in Shaanxi Province are all low-yield areas.
The altitude of the entire region is 1000-1400 m, and the soil is mainly chestnut soil. The continental climate is markedly characterized by cold, little rain, barren soil, and poor natural conditions. The average temperature of the coldest month is -17 to 11°C, and the absolute minimum temperature is -38 to 27°C. Annual precipitation is 309-496 mm, with most areas around 300 mm, and precipitation during the wheat growing period is only 94-168 mm. The cropping system is mainly one crop per year, with a few areas having three crops in two years. Wheat varieties in this region are spring type, sensitive to photoperiod response, and have a growing period of 90-120 days. The sowing period is from mid-March to mid-April, and maturity is around early July, at the latest until the end of August. The main diseases in the entire region are leaf rust, stem rust, yellow dwarf disease, and dwarf mosaic; insect pests are mainly wheat stem maggot and armyworm. Early-spring drought, high-temperature forced ripening and dry hot wind damage in the later period, and soil salinization in the Hetao Irrigation District are all major problems in wheat production. For yield-increasing measures, planting systems such as fallow rotation should be implemented to improve soil fertility; in irrigation districts, furrow and border irrigation should be promoted, canal system matching should be carried out well, the irrigation system should be improved, and soil salinization should be prevented. According to differences in precipitation between the south and north of the region, it can be divided into two subregions: the northern arid subregion and the southern semi-arid subregion.
3. Northwest Spring Wheat Region
The Northwest Spring Wheat Region is mainly Gansu Province and the Ningxia Hui Autonomous Region, and also includes western Inner Mongolia Autonomous Region and parts of eastern Qinghai Province. Wheat field area accounts for about 4% of the national total, and total output reaches about 5%. Its unit yield is second only to the Middle and Lower Yangtze Winter Wheat Region nationwide, and ranks first among all spring wheat regions; there are large differences between areas, among which the unit yields of the Hexi Corridor Irrigation District in Gansu Province and the Ningxia-Yinchuan Yellow River irrigation district are relatively high.
The Northwest Spring Wheat Region is located inland, weakly affected by oceanic monsoons, and some areas have an arid desert climate. The altitude is 1100-2240 m, and the soil is mainly brown calcareous soil and gray calcareous soil, loose in structure and prone to wind erosion and desertification. In the Loess Plateau area, gullies are deep and slopes steep, water and soil loss is serious, and soil fertility is poor. The average temperature of the coldest month is -9.3 to 7.5°C, and the absolute minimum temperature is -27 to 23°C. Light energy resources are abundant, heat conditions are relatively good, and the diurnal temperature range is large; there are many clear days, long sunshine, and strong radiation, which are favorable for wheat photosynthesis and dry matter accumulation. But annual precipitation is only 86-335 mm, and precipitation during the wheat growing period is 52-181 mm, making it one of the regions with the least precipitation in China, and evaporation is also high. Wheat growth mainly depends on irrigation with water from the Yellow River and snowmelt from the Qilian Mountains. In the later period, dry hot wind damage often occurs, and wheat rust, smut, and wheat midge are all major diseases and pests of wheat in this region. The cropping system of the entire region is one crop per year. Wheat varieties are spring type, and the growing period is 120-130 days. Sowing is in early March, and maturity is from mid-July to early August. According to topography, precipitation, and other conditions, the entire region can be divided into 4 subregions: desert arid, Ningxia-Yinchuan irrigation district, Longxi hills, and Hexi Corridor.
4. Xinjiang Winter-Spring Wheat Region
The Xinjiang Winter-Spring Wheat Region is located in the Xinjiang Uygur Autonomous Region. The wheat planting area of the entire region is about 4.6% of the national total, and total output is about 3.8% of the national total. Among this, wheat area in northern Xinjiang is about 57% of the entire region, mainly spring wheat, and its unit yield is also higher than that of southern Xinjiang; southern Xinjiang is mainly winter wheat, with an area more than 3 times that of spring wheat.
The Xinjiang Winter-Spring Wheat Region has a continental climate, dry climate, and scarce rainfall, but it has abundant iceberg and snowmelt water resources, and groundwater resources are also relatively abundant. There are many clear days, long sunshine, and strong radiation. Northern Xinjiang is located between the Tianshan Mountains and the Altai Mountains, with low temperatures; the average temperature of the coldest month is -18 to 11°C, and the absolute minimum temperature is -44 to 33°C, but because snow often covers the ground in winter, wheat can generally overwinter safely in normal years. In years with little snow, winter wheat seedling death during overwintering is more serious. Annual precipitation is 163-244 mm; precipitation during the wheat growing period is 107-190 mm for winter wheat and 83-106 mm for spring wheat. Temperatures in southern Xinjiang are higher than in northern Xinjiang; the average temperature of the coldest month is -12.2 to 5.9°C, and the absolute minimum temperature is -28.0 to 24.3°C; annual precipitation is only 13-61 mm, precipitation during the wheat growing period is 8-48 mm for winter wheat and 7-39 mm for spring wheat, but both can be irrigated with iceberg and snowmelt water. The soil in northern Xinjiang is mainly brown calcareous soil and gray-brown soil, while in southern Xinjiang it is mainly brown desert soil. The cropping system is mainly one crop per year, while southern Xinjiang also has one year with two crops. Winter wheat varieties are strongly winter type and sensitive to photoperiod response. Preventing low-temperature freeze damage, drought, soil salinization, and dry hot wind damage in the late growing period are all important issues in wheat production in this region. The sowing period for winter wheat is around mid-September, and it matures at the end of July or early August of the following year. Spring wheat in northern Xinjiang is sown around early April and matures around early August; in southern Xinjiang it is sown from late February to early March and matures in mid-July. According to the direction of the Tianshan Mountains, the entire region can be divided into two subregions: southern Xinjiang and northern Xinjiang.
5. Qinghai-Tibet Spring-Winter Wheat Region
The Qinghai-Tibet Spring-Winter Wheat Region includes the Tibet Autonomous Region, most of Qinghai Province, southwestern Gansu Province, western Sichuan Province, and northwestern Yunnan Province. The entire region is mainly forestry and animal husbandry; wheat planting area and total output are both about 0.5% of the national totals, among which spring wheat is predominant, accounting for about 65.3% of the total wheat area of the entire region. Since the mid-1970s, winter wheat has developed rapidly in the Yarlung Zangbo River valley area of southern Tibet, and the year-round winter wheat area in Tibet accounts for about 40-80% of the total wheat field area. The middle reaches of the Yarlung Zangbo River valley and areas such as Lvdu have low and flat terrain, fertile soil, and developed irrigation, and are the main wheat producing areas of this region. The altitude of agricultural areas is generally 3300-3800 m, with a cool climate, no severe summer heat, and no severe winter cold; the average temperature of the coldest month is -4.8 to 0.1°C, and the absolute minimum temperature is -25.1 to 13.4°C. Winter temperatures are relatively low and stable, and the duration is long; winter wheat takes two months from greening to jointing and from heading to maturity; moreover, sunshine duration is long, the diurnal temperature range is large, photosynthesis intensity is high, net photosynthetic efficiency is high, and yields are also relatively high. The sowing period for winter wheat is late September, and for spring wheat late March to early April, and both mature from late August to mid-September. The entire growing period of winter wheat lasts about 330 days, and some do not mature until a full year; spring wheat lasts 140-170 days. Annual precipitation in the entire region is 42-770 mm, averaging about 450 mm. Among this, annual precipitation in southern Tibet is 280-764 mm, usually around 500 mm. Precipitation during the wheat growing period is 250-590 mm for winter wheat and 224-510 mm for spring wheat. The cropping system is one crop per year. The Qinghai-Tibet Plateau soil is mostly alpine soil, with thin soil layers and few available nutrients. The main agricultural areas on both banks of the Yarlung Zangbo River basin mostly have calcareous alluvial soil, while the Qaidam Basin is mainly gray-brown desert soil. Winter wheat varieties are strongly winter type and sensitive to photoperiod response. Building water conservancy facilities, leveling land, careful cultivation and management, and improving irrigation conditions to prevent soil salinization are key yield-increasing measures in this region. The entire region can be divided into 3 subregions: the Qinghai lake-ring basin, the Sichuan-Tibet Plateau, and southern Qinghai-northern Tibet.
6. Northern Winter Wheat Region
The Northern Winter Wheat Region includes the area south of the Great Wall in Hebei Province, central and southeastern Shanxi Province, the northern area south of the Great Wall in Shaanxi Province, the Liaodong Peninsula in Liaoning Province, southern Ningxia Hui Autonomous Region, the Longdong area of Gansu Province, and the two municipalities of Beijing and Tianjin. The wheat field area and total output of the entire region are about 9% and 6% of the national totals, respectively, and about 31% of the region's grain crop planting area. The average wheat unit yield is lower than the national average.
The Northern Winter Wheat Region is located at the northern boundary of winter wheat; apart from most of Hebei Province being plain and the Liaoning coastal area being hilly, the altitude is 750-1260 m. Soils include cinnamon soil, loessal soil, and saline soil. Among these, cinnamon soil is predominant, with low humus content, but moderate texture, good permeability and tillage properties, a deep weathered layer, and good moisture retention and drought tolerance. The continental climate is obvious; the average temperature of the coldest month is -7.7 to 4.6°C, and the absolute minimum temperature is -24 to 20.9°C. In normal years winter wheat can basically overwinter safely, but interannual variability is large. In low-temperature years freeze damage occurs from time to time, and winter wheat freeze damage is especially severe in the transitional edge zone between winter and spring wheat regions. Annual precipitation is 440-660 mm, mostly concentrated in summer and autumn, with precipitation from July to September accounting for about 44% of the annual total. Precipitation during the wheat growing period is 143-215 mm. Drought damage is relatively serious, especially spring drought. The cropping system is mainly three crops in two years, among which dryland is mostly one crop per year, and the one-year-two-crop system has developed in irrigated areas. Variety types are winter or strongly winter type, sensitive to photoperiod response, with a growing period of about 260 days. Diseases include stripe rust, leaf rust, powdery mildew, and yellow dwarf disease; insect pests are mainly underground pests, red spiders, and wheat aphids. Dryland sowing is in early to mid-September, irrigated land around September 20; maturity is usually in mid-to-late June, with a few late until early July. Strengthening farmland capital construction and soil and water conservation, building water conservancy facilities, increasing fertilizer application, and selecting cold-resistant and drought-tolerant varieties are key measures for increasing wheat yield in this region. The entire region can be divided into 3 subregions: the Yanshan-Taihang Mountain piedmont plain, the Shanxi-Hebei mountain and basin area, and the Loess Plateau gully area.
7. Huang-Huai Winter Wheat Region
The Huang-Huai Winter Wheat Region includes all of Shandong Province, most of Henan Province (except the Xinyang area), central and southern Hebei Province, the Huaibei area of Jiangsu and Anhui provinces, the Guanzhong Plain area of Shaanxi Province, southwestern Shanxi Province, and the Tianshui area of Gansu Province. The wheat area and total output of the entire region account for about 45% and 48% of the national wheat field area and total output, respectively, and about 44% of the region's grain crop planting area, making it China's main wheat producing area.
The Huang-Huai Winter Wheat Region has low and flat terrain; except for Longdong, Guanzhong, and southwestern Shanxi, as well as some hilly areas where the altitude is slightly higher, the main wheat areas are all less than 100 m. Soil types are mainly calcareous alluvial soil, with some yellow soil and brown soil, with good texture and relatively high productivity. The entire region has a mild climate and relatively suitable rainfall. The average temperature of the coldest month is -3.4 to 0.2°C, and the absolute minimum temperature is -22.6 to 14.60°C. Winter wheat overwintering conditions are good, and wheat seedlings can usually remain green in winter. Annual precipitation is 580-860 mm, and precipitation during the wheat growing period is 152-287 mm. In rainy years it can basically meet the needs of wheat growth, but areas farther north often suffer drought damage because of uneven rainfall distribution or interannual variation. The region's water resources are relatively abundant, and irrigation can be developed. The cropping system in irrigated areas is mainly one year with two crops, while dryland and hilly areas mostly practice three crops in two years; some wheat fields on dryland in Guanzhong of Shaanxi, western Henan, and southern Shanxi have one crop per year. Variety types are mostly winter or weakly winter type, with moderate to sensitive photoperiod response, and a growing period of about 230 days. In the south of this region, spring-type varieties are planted as late-season wheat. General diseases and pests are roughly the same as in the Northern Winter Wheat Region, but take-all and soilborne mosaic virus are relatively serious in the Jiaodong area of Shandong Province. Dry hot wind damage in the late wheat growing period is widespread and serious. The suitable sowing period is generally early October, but some areas often cannot sow at the suitable time for various reasons, resulting in a large area of late-season wheat and low yields, thus affecting wheat production in the entire region. Therefore, rationally arranging crop rotation and sowing dates is key in wheat production. Wheat in the entire region matures from late May to early June. According to climate, topography, and other conditions, the entire region can be divided into 3 subregions: the Huang-Huai Plain, the Fen-Wei River valley, and the Jiaodong hills.
8. Middle and Lower Yangtze Winter Wheat Region
The Middle and Lower Yangtze Winter Wheat Region reaches the Huai River to the north, the western Hubei mountains and western Hunan hilly areas to the west, the East China Sea coast to the east, and the Nanling Mountains to the south. It includes most of Jiangsu, Anhui, Hubei, and Hunan provinces, all of Shanghai Municipality and Zhejiang and Jiangxi provinces, and the Xinyang area of Henan Province. The wheat area of the entire region is about 11.7% of the national total wheat field area, and total output is about 15% of the national total. The unit area yield is high, ranking first among all wheat regions in the country, but development between provinces is extremely uneven. Among them, Jiangsu Province has the highest yield, while the whole of Jiangxi Province and southwestern Hunan Province are low-yield areas. Wheat is not a major crop in the entire region; wheat area in Hubei, Anhui, and Jiangsu provinces is only about 20% of the grain crop planting area, while in Jiangxi, Hunan, and Zhejiang provinces it is only about 5%. The entire region has a mild climate and low, flat terrain; in coastal areas such as Shanghai and Ningbo the altitude is less than 10 m, and in other areas it is only about 50 m. The average temperature of the coldest month is 1.0-7.8°C, and the absolute minimum temperature is -15.4 to 4.1°C. Annual precipitation is 1000-1800 mm, and precipitation during the wheat growing period is 360-830 mm. Wheat growth not only does not require irrigation, but wet damage often occurs. Areas such as Fuzhou in southern Jiangxi Province even have wheat planting affected by severe wet damage. The cropping system is mainly one year with two crops, and some areas have a three-crop system. Wheat varieties are mostly weakly winter or spring type, insensitive to photoperiod response, with a growing period of about 200 days. The sowing period is from mid-to-late October to early-to-mid November, and maturity is in late May of the following year. In addition to fusarium head blight, diseases also include powdery mildew, leaf rust, stripe rust, sheath blight, and leaf blight. Matching field ditches with canals to lower and control groundwater in order to manage wet damage, supplemented by chemical disease control, is a key measure for increasing wheat yield in this region. The entire region can be divided into 4 subregions: the Jiang-Huai Plain, the riverside and lakeside area, the southern Zhejiang-Anhui mountains, and the Hunan-Jiangxi hills.
9. Southwest Winter Wheat Region
The Southwest Winter Wheat Region includes all of Guizhou Province, most of Sichuan and Yunnan provinces, southern Shaanxi Province, southeastern Gansu Province, and western Hubei and Hunan provinces. The wheat planting area of the entire region accounts for about 12.6% of the national total wheat field area, and total output is about 12.2% of the national total. Among this, the Sichuan Basin is the main producing area, with area and total output accounting for about 53.6% and 63% of the entire region, respectively.
The Southwest Winter Wheat Region has complex topography, with mountains, plateaus, hills, and basins all present. The altitude is 300-2000 m. The entire region has a mild climate and relatively good water and heat conditions, but insufficient light. The average temperature of the coldest month is 2.6-6.2°C, and the absolute minimum temperature is -11.7 to 5.2°C; among this, the average temperature of the coldest month in the Sichuan Basin is 5.2-7.5°C, and the absolute minimum temperature is -5.9 to 1.7°C. Apart from southeastern Gansu Province, where rainfall is somewhat low, annual precipitation in the remaining areas is 772-1510 mm, and precipitation during the wheat growing period is 279-565 mm. Soil types are mainly red soil and yellow soil; western Hubei, western Hunan, and the Sichuan Basin are mainly yellow soil, while red soil is mainly distributed in the Yunnan-Guizhou Plateau. The cropping system in most areas is a rice-wheat double-cropping one-year-two-crop system. Wheat varieties are mostly spring or weakly winter type, insensitive to photoperiod response, with a growing period of 180-200 days. Stripe rust and powdery mildew are relatively serious in the entire region, with occasional occurrence of fusarium head blight. Insect pests are mainly aphids. There are natural disasters such as wet damage, low-temperature cold damage, and high-temperature forced ripening in the later period. In plain wheat areas, the suitable sowing period is late October to early November, and maturity is in early to mid-May. In hilly and mountainous areas, the sowing period is slightly earlier and the maturity period slightly later. In the entire region, in addition to strengthening control of wet damage and disease and insect damage, improving sowing methods in plain rice-wheat double-cropping areas, strengthening soil and water conservation and farmland construction in dry hilly areas, and increasing fertilizer application to improve soil fertility are all key measures for increasing wheat yield. This region can be divided into 3 subregions: the Yunnan-Guizhou Plateau, the Sichuan Basin, and the southern Shaanxi-western Hubei hills.
10. South China Winter Wheat Region
The South China Winter Wheat Region includes all of Fujian, Guangdong, Guangxi, and Taiwan provinces (autonomous regions) and southern Yunnan Province. The wheat planting area is about 2.1% of the national total wheat field area (data for Taiwan Province are missing; same below), and total output is about 1.1% of the national total. Wheat is not a major crop in this region; its planting area accounts for only about 5% of the grain crop area, and the area has been very unstable over the years.
Nearly 90% of the South China Winter Wheat Region is mountainous and hilly; the total area of the Pearl River Delta, the Chaoshan Plain, and the small coastal plains of southern Fujian is no more than 10%. The altitude of mountainous areas is about 1000 m, hilly areas about 200 m, and coastal plains all less than 100 m. The soil is mainly red soil and yellow soil. The entire region has a warm and hot climate with no snow in winter; the average temperature of the coldest month is 7.9-13.4°C, and the absolute minimum temperature is -5.4 to 0.5°C. Annual precipitation is 1280-1820 mm, and precipitation during the wheat growing period is 320-450 mm. Water and heat resources are abundant, but rainfall distribution among seasons is uneven, especially in that it is poorly coordinated with the water requirement pattern during the wheat growing period. The seedling stage is dry with little rain, while during grain filling there is much rain and little sunshine with high humidity, affecting wheat flowering, grain filling, and seed setting, and often leading to damage from fusarium head blight, rust, and other diseases. The cropping system is mainly one year with three crops, and some areas practice rice-wheat double cropping or three crops in two years. Wheat varieties are spring type, slow to respond to photoperiod, with a growing period of about 120 days. Diseases are mainly fusarium head blight and powdery mildew, followed by stem rust and leaf rust. Insect pests include aphids and armyworms. The maturity period is rainy, and pre-harvest sprouting is serious; yield-increasing measures are mainly opening ditches to drain water and prevent wet damage and appropriately arranging the sowing period. The suitable sowing period is mid-to-late November, and maturity is earliest in mid-to-late March, generally from late March to early April. The entire region can be divided into two subregions: mountainous and hilly areas and coastal plains.
Further reading: High-yield wheat planting techniques, the difference between spring wheat and winter wheat in China