Change Of Fiber Quality In Machine-harvested Cotton In The Xinjiang And Further Survey Of Promising Approaches For Improving

The cotton production has increased rapidly during the last decade in the Xinjiang Region.The Xinjiang Region produced 359×10~4 t of cotton in 2016,accounting for 68%of China's total.The use of machine harvesters was the most wonderful benefit of reducing substantially cotton production costs and promoting the reform of cotton production to modern agriculture.However,these reductions in fiber quality had caused declines in the sale of machine-harvested cotton from Xinjiang.Most cotton frading companies and textile factories will not buy or use machine-harvested cotton.Thus,an urgent problem was to determine how cotton quality can be improved in the Xinjiang Region.Cotton fiber quality was determined by three interrelated,but different factors:field production conditions,harvesting methods,and cleaning processes.The primary objective of this study was to systematically determine changes of fiber quality affected by field production conditions,harvesting methods and cleaning processes,and to inveatigate the reason for poor lint quality.Based on these,a secondary objective was to analyse the fiber damage affected by temperature,defoliation,machine-harvesting,and cleaning processes in the Xinjiang Region.The main results were as follows.1.Changes of fiber quality and how to reduce fiber damage on machine-harvested cotton in XinjiangFiber length was the longest in the Xinjiang Region and longer than 0.20 mm compared with the national average.Fiber strength was the lowest in the Xinjiang and was only approximately 28 cN/tex.In the Xinjiang,the percent of 27 mm grade on length decreased,while that of 29 mm grade decreased and there was wide fluctuation in 29 mm length grade among years.The percentages of stronger grade and strong grade on fiber strength in the Xinjiang were lowest among five provinces and only 3.0%and 20%,respectively.While the percentage of poor grade on fiber strength accounted for 10%was the most among five provinces.Therefore,there was the situation of fiber quality in the Xinjiang that the percentage of worse fiber increased while that of better fiber decreased gradually.Field production conditions and harvesting methods caused more variability in fiber damage than cleaning processes.Under field production conditions,fiber strength of 35%of the cultivars was reduced by more than 2 cN/tex and fiber length of 12%was reduced by more than 2 mm.Machine harvesting reduced fiber length by more than 2 mm at 17%of the experimental sites.Cleaning processes caused fiber damages that fiber quality reduced one to two units accounted for 84%of samples.Cotton fiber damage as influenced by field production conditions,harvesting methods,and cleaning processes.The crucial point about the phenomenon was that how to reduce the foreign matter content of machine harvested cotton.However,field production conditions increased fiber strength of 27%of the cultivars compared with variety trial reports,machine harvesting increased fiber length and fiber strength at 48%and 33%of the experiment sites compared with hand harvesting.2.Temperatures have differential effects on fiber strength and cellulose depositionHigh night-time temperature during from anthesis to the onset time of rapid cellulose deposition significantly decreased the average rate of cellulose deposition and cellulose content in this temperature regime,which in turn significantly decreased fiber strength.Elevated night-time temperature between the onset and termination times of rapid cellulose deposition would make for higher fiber strength,due to delay the termination time and a suitable rate of rapid cellulose deposition.No significant difference in fiber strength and cellulose deposition characters between elevated night-time and ambient temperatures.Therefore,the differential effects of elevated night-time temperatures on fiber strength resulted from the differences in the average rate from anthesis to the onset time of rapid cellulose deposition.Growing degree days was the factor associated with cellulose deposition in cotton fiber.The relationship between both was going to go the other way during the different fiber developing.During the period from anthesis until the onset of rapid cellulose deposition,the average rate of cellulose deposition decreased as growing degree days increased,that had an unfavorable about fiber strength.During the period of rapid cellulose deposition,growing degree days increased significantly the cellulose deposition rate during from anthesis until the onset of rapid cellulose deposition and the duration time of rapid cellulose deposition,then fiber strength increased.Therefore,growing degree days resulted in different effects on fiber strength during the different fiber developing,the main reason was that growing degree days caused variability effects on the average cellulose rate during the period from anthesis until the onset of rapid cellulose deposition.3.Effects of Defoliation timings on fiber quality and leaf abscission of cottonCotton leaf abscission was the highest and had from 55%to 79%at 7.0±1.0 days after defoliation application.And growing degree days and maximum temperature was positively correlated with the cotton leaf abscission during 7.0±1.0 days after defoliation application.If obtaining more than 55%leaf abscission at 7.0±1.0 days after defoliation application,maximum temperature and growing degree days should be more than 27.2?and 4.6?/d,respectively.Therefore,the critical period promoting the good leaf abscission of cotton was during 7.0±1.0 days after defoliation application,and the dominant temperature factors influencing cotton leaf abscission was the maximum temperature and growing degree days.Furthermore,the drying leaf caused by applying defoliant and leaf hairiness should be focused to obtaining rapid and complete defoliation of cotton during 7.0±1.0 days after defoliation application.Defoliant had a little effect on fiber length and fiber damage was from-0.5 mm to 0.0 mm,while there was one half of cotton varieties for increasing after deforliation.Fiber strength was affected significantly by defoliation and fiber damage was from-4 c N/tex to 0 cN/tex,then the amplitude of fiber damage became more than broadly.However,there was more than 61%cotton varieties for increasing on fiber strength.Fiber strength had the positive correlation coefiicient with cotton boll volume,and cotton boll volume had the positive relationship with boll growth period.But fiber strength decreased as boll growth period increased.Therefore,there was a method for calculating defoliation timings based on the boll growth period and fiber damage on fiber strength.4.Effect of cotton mechanical harvest on fiber qualities in XinjiangThere was a significant difference of machine picking on fiber quality.Fiber length and micronaire had no significant changes between machine picking and hand picking,and little changes in multi-site plots and varieties.Compared hand picked cotton,fiber strength,uniformity index and spinning consistency index decreased significantly.Especially,changes of fiber strength and spinning consistency index were lager,at less than 11%and 26%separately,and 63%of varieties decreased significantly.Change of short fiber index was most significance among six fiber quality indicators,short fiber index of cotton picker increased 51%than it of hand picking cotton,at more than 90%and 130%separately in multi-site plots and varieties.5.Cleaning processes caused fiber damage of machine-harvested cottonSeed cotton cleaning had mixed effects on fiber strength.Seed cotton cleaning reduced the fiber strength of cotton from seven fields.Damage to fibers from four fields was significant,averaging 1.42cN/tex.The second and third cleaning caused great fiber damage by 0.65 cN/tex per cleaning.Strength damage was related to cotton leaf adhesiveness but not to foreign matter content.In conclusion,seed cotton cleaning had varying effects on fiber strength due to leaf cleanability.Variety selection should focus on leaf and bract traits so as to improve leaf cleanability to>45%.Ginning and lint cleaning had no significant effect on fiber strength and significantly affected both fiber length and short fiber index.Fiber length was reduced by more than 1.00 mm from six of thirteen fields after lint cleaning,then the damage rate on short fiber index from elven of thirteen fields was more than 20%.The third lint cleaning caused great fiber damage,reducing fiber length by 0.35 mm and increasing short fiber index by 0.65%.In conclusion,the lint should be cleaned by one lint cleaner in the Xinjiang Region.A stage of lint cleaning was sometimes omitted when the foreign matter content of lint was little.