Cotton is a crop that likes temperature, light, waterlogging and drought. The active accumulated temperature in the whole growth period is 4300℃, the water demand is about 800mm, and the sunshine hours are 1 100 h. The climatic conditions required for cotton planting in Jiangxi Province in each growth period are as follows:
1) seedling stage (from mid-April to early June): cotton needs about 90mm of water, and cotton seedlings are suitable for growing at 25℃, and can only maintain life at 15℃.
2) Bud stage (from mid-June to late June): The water requirement for cotton bud stage is 80 ~ 120 mm, during which the rainfall is moderate, the temperature rises rapidly, and the potential fertility of plough layer is brought into play.
3) Flowering and bolling period (from early July to late August): This period is the most vigorous period for cotton to need water and fertilizer, and the water demand is about 250 ~ 300mm. During this period, summer drought is the main problem in the whole province, and most areas cannot meet the demand for cotton growth.
4) Flocculation period (from early September to mid-June, 10): the water demand of cotton is about 100mm, and precipitation is still suitable in most parts of the province.
Climatic regionalization of cotton
The average daily temperature stably passes through 15℃, the interval between the first day and the last day is greater than 150d, and cotton can be planted in areas with accumulated temperature above 3300℃ ≥ 15℃. The climatic conditions in the province can meet the needs of cotton planting and growth. However, in order to obtain high and stable yield and good quality of cotton, in addition to varieties and production management factors, the climatic conditions in its growing period are the key constraints, which is also the reason why cotton planting in Jiangxi Province is mainly concentrated in northern Jiangxi. In order to obtain high and stable yield and form good quality, cotton needs to meet the following climatic conditions:
1) The active accumulated temperature (σ t) during the whole breeding period is above 4300℃;
2) The days when the temperature is above 35℃ (DT≥35℃) are less than 20 days;
3) Flowering-blooming period: the daily temperature difference is more than 7℃;
4) Flowering-blooming period: the average daily sunshine should be more than 8 hours, and the sunshine hours (h) in the whole growth period should be more than 1 150h;
5) Flowering and bolling period: Precipitation should account for more than 40% of cotton water demand in the same period.
According to the above climate indicators, the light, temperature and water resources in the cotton growing season in Poyang Lake area were analyzed. Except in alpine areas, the accumulated temperature of cotton in Poyang Lake during the growing season and the whole growth period can reach above 4300℃, and the thermal conditions can meet the needs of cotton growth. In addition, cotton in Poyang Lake area is mainly planted in irrigated farmland, and the water conditions needed during flowering-bolling period can basically meet the needs of cotton growth, which poses a threat to cotton yield. Therefore, the yield and quality of cotton are mainly affected by high temperature, sunshine and daily range during its growth period.
Cotton is a warm crop. The suitable temperature for growth and development after emergence is 25 ~ 30℃, 35 ~ 37℃ can barely grow and develop, and above 40℃ will damage tissues. Therefore, the high temperature weather during the growth period has a great influence on cotton yield and quality. According to the statistical analysis of the days when the daily average temperature of each meteorological station in Poyang Lake area is ≥35℃, the areas with the least days when the daily average temperature is ≥35℃ are mainly concentrated in the counties along Poyang Lake, mainly distributed in most counties under the jurisdiction of Jiujiang City, such as Hukou, Pengze, Xing Zi, Duchang, Jiujiang, De 'an and Yongxiu. From the analysis of high temperature conditions, it can be seen that the number of high temperature days in Jiujiang city in Poyang Lake area is less, which is beneficial to the growth and quality of cotton.
Cotton is not only a warm crop, but also a light crop. With Poyang Lake as the center, the sunshine hours in the cotton growing season in Poyang Lake area gradually decrease from the inside out. Only along the lake county, the sunshine hours in cotton growing season are above 1 130h, which basically meets the needs of cotton growth; In the periphery of the lake area, the sunshine hours gradually decreased to below1050 h. Therefore, in Poyang Lake area, only the light conditions along the lake county can meet the growth and development of cotton.
According to the conditions of high temperature days ≥35℃ and limited sunshine during the cotton growing period, it is concluded that the areas suitable for cotton planting in Poyang Lake area are concentrated in the lakeside area in northern Jiangxi (Figure 6, Attached Figure 4-7), that is, in some counties under the jurisdiction of Jiujiang City in Poyang Lake area, such as Hukou, Xing Zi, Duchang, Jiujiang, Yongxiu and De 'an. This is why cotton in the whole province is mainly concentrated in northern Jiangxi.