Effect of climate change on cotton growth period and yield in Kashgar City, Xinjiang Uygur Autonomous Region

This paper analyzed climate change and the responses of cotton growth period and yield to warming climate since 1961 in Kashgar, Xinjiang Uygur Autonomous Region, China. The paper used the methods of tendency, detection and trend coefficient to determine the rate of climate changes of average temperature, maximum temperature, minimum temperature, precipitation and sunshine duration for the period 19612013. The study also analyzed cotton growth period, yield amount, and characteristics of pre-summer boll, summer boll and autumn boll for the past 23 years (19902013) of ground-truth data in the national reference stations of Kashgar (75°59′E, 39°28′N). The results showed that average annual temperature, average seasonal temperature, average maximum and average minimum temperature increased significantly in the past 53 years (19612013). The rates of warming in annual temperature, spring temperature, summer temperature and autumn temperature were respectively 0.250.47 ℃10a^-1 (P< 0.01), 0.240.47 ℃10a^-1 (P< 0.05), 0.090.37 ℃10a^-1 and 0.320.46 ℃10a^-1 (P< 0.01). Among the variables, the trends of increase in average minimum temperature in spring and autumn were of significant. Yearly precipitation apparently increased at a rate of 6.16 mm10a1. Spring precipitation declined at a rate of 0.44 mm10a1, while summer and autumn precipitations increased at rates of 2.10 mm10a^-1 and 2.23 mm10a^-1(P < 0.05), respectively. There was significant positive trend in sunshine duration, increasing at a rate of 31.3 h10a^-1 (P< 0.05) at annua^-1 scale, 16.16 h10a^-1 (P< 0.01) during spring, 9.84 h10a^-1 (P< 0.05) during summer and 4.27 h10a^-1(P< 0.01) during autumn. The highest increase was in spring. The date of the latest frost advanced (1.3 d10a^-1), the date of the first frost delayed (1.4 d10a^-1) and then frost-free period lengthened (1.0 d10a^-1) in the past 53 years from 1961 to 2013. Over the past 23 years (19902013), average sowing date, seedling stage, third true leaf stage, fifth true leaf stage, squaring stage, flowering stage, cracked-bell stage and boll-opening stage of cotton apparently advanced to different degrees, with the trend in squaring stage as most obvious — 6.6 d10a^-1 (P< 0.01). Cotton sub-stop growth season date delayed by about 4.2 d10a^-1 (P< 0.01), the extended growth period was very favorable for cotton yield and quality. The numbers of pre- summer boll, summer boll and autumn boll of cotton significantly increased at respective rates of 0.58 bolls10a1, 0.92 bolls10a1 and 0.49 bolls1 a^-1. Average yield per acre increased in the past 23 years (19902013) by 373.5 kghm210a^-1 (P< 0.01). The factors influencing cotton growth period and yield were temperature, precipitation and sunshine duration which changed frost days, last frost day and frost-free period, suggesting that warming climate very much favored cotton production and quality in Kashgar region. This study suggested that cotton yield was positively correlated with last frost date, first frost date and frost-free period. Last frost date apparently advanced, first frost date apparently delayed, and frost-free period lengthened, enhancing cotton production in the study area.