Study On The Technology Of Chemical Topping With DPC~+ And Its Supporting Measures In The Yellow River Valley Region Of China

Cotton is a perennial plant with an indeterminate fruiting pattern.Manual topping is one of production management measures.Chemical topping which applying plant growth regulators to reduce differentiation rate of apical bud on cotton main stem and sympodial,and controlling elongation growth of upper main stem internodes,plays a similar role as manual topping.The study conducted in Hejian and Shangzhuang sites from 2012 to 2016 with chemical topping with fortified DPC which is 25%mepiquat chloride water aqua,whose components in assistants damaged epidermis of tender tissues,and had longer period of validity then common DPC soluble powder.The strategy was hereafter referred to as DPC.Besides,we also studied its supporting measures which could explaining technology principle from accumulation and distribution of shoot dry matter.All aimed at to accelerate realization of full mechanization of cotton production in Yellow River cotton belt.And key results were as follows.1.Chemical topping with DPC~+ was significantly influenced cotton growth when compared with manual topping,which remodeled cotton plant architecture to being more compacted.Plant height,nodes of main stem,number of sympodials were significantly higher than manual topping,and increased range 4.5-14.8 cm,3.1-5.4 nodes,1.8-7.4 branches,separately,especially shortened length of top sympodials,whose only range 1?3 cm.Application time of DPC~+ from mid July to late July and its doses from 750 to 1500 mL/hm~2 had no obvious effects on plant architecture,yield and fiber quality.while sprayed in late July,the cotton seed yield were all higher than manual topping,but the dose of 1500 mL/hm~2 may delay maturity of late bolls,so we should avoid using highest dose in peak boll setting period.When compared with DPC~+,the conventional DPC application alone(DPC)showed a weaker control in terms of plant height and the number of sympodials,and possibly had a risk of reduced yield in rainy years or at higher plant density.2.When compared with Xinkang 4,Shikang 126,Guoxin 3 was more sensitive to DPC~+ chemical topping,for large control intensity on increasing less of plant height,number of main stem and sympodials.Guoxin 3's chemical topping with DPC~+ had higher yields than Xinkang 4,and significantly higher than Shikang 126.chemical topping with DPC~+ had no effects on fiber quality(except for macronaire).3.With plant density increasing,Cotton with different topping ways showed some characters like,plant height decreased,less sympodials,shorten length of lower and middle fruiting branches,larger LAI and increased accumulation of shoot dry matter.The effects of plant density on yield and maturity varied with years,one side it has not affect yield and maturity in 2012 and 2013,on the other side,high plant density reduced yield and delayed maturity in 2013 and 2016 which rainy in July.Plant density did not significantly affect chemical topping with DPC~+.4.Nitrogen rates did not significantly affect cotton plant growth,yield and its components,accumulation and distribution of shoot dry matter,maturity and fiber quality.And also,nitrogen rates from 0 to 210 kg N/hm~2 had no influence on effects of chemical topping with DPC~+.That is to say requirements of chemical topping technology on planting density and nitrogen rates may not harsh,which is conducive to the promotion of the technology.In summary,the application of chemical topping with DPC~+ is basically feasible in the North of Yellow River valley of China.And while make a decision whether applying conventional DPC alone or applying DPC~+,the meteorological factor,especially precipitation and plant density should be considered carefully.We suggest that cotton chemical topping with fortified MC possibly does not require specific plant density and nitrogen rate,which is helpful for the generalization of this simplified technique in the Yellow River valley region.