| Mepiquat chloride(MC)is an effective way to suppress excessive growth,hasten maturity and increase harvesting efficiency as well as the key technology of shaping suitable plant architecture for mechanical harvesting of cotton.The effect of MC varied with environmental conditions and other cultivation measures in production.Therefore,the proper time and dose of MC should be determined after considering various factors.The experiments were conducted in Hejian city,Hebei Province,during 2013 and 2014.Plant populations were 6.5 and 11.4 plants m-2,and the two cultivars SCRC36 and Han7860 were used.MC was applied at the seedling(early June),squaring(mid-June),early bloom(early July),full bloom(mid-July),and post-topping stage(the end of July),respectively.The objectives of this study were to detemine the location and quantitative effect of single MC application at different growth stages and its interaction effect with climate,plant density and variety on the cotton growth rate,plant habit,yield and yield components,in order to provide guidance for reasonable MC application strategy and lay the foundation for high yield of cotton cultivation in the Yellow River cotton valley cotton region.(1)The location and quantitative effect of application of MC at different growth stages on cotton plant habit.The effect of MC increased first and then decreased,the effect was the highest after 10-15 days,and gradually disappeared after 25-30 days.The validity period of MC was closely related to climate weather and dose,but not related to cultivar and density.When the climate was drought and the larger dose of MC was applied,the validity period is generally longer.For example,when MC was applied at the squaring stage,The rainfall in June 2013 was 80.1 mm,The validity period of low dose MC(7.5 g ha-1)and high dose MC(30g ha-1)were 10 and 25 d.the rainfall In June 2014 was 30 mm,the effective periods of low dose MC(7.5 g ha-1)and high dose MC(30g/ha-1)were 23 and 32 d.The effect of MC application at different growth stages on main stem interrnode length and fruit node length was different.The control range of MC on main stem internode length at the seedling,squaring,early bloom and full bloom stage was 5-10,10-13,15-21 and 18-21 in 2013,respectively,and 4-12,9-18,16-18 and 18 in 2004,respectively.In 2013,MC application at the seedling,squaring,early bloom,and full bloom stage significantly affect the first fruit node length of 1,2-6,8-16 and 11-16 fruit branches,the second fruit node length of 0,3-4,5-16 and 10-16 fruit branches,and the third fruit node length of 0,3-4,2-14 and 9-15 fruit branches,respectively.In 2014,MC was applied at the seedling,squaring,early bloom,and full bloom stage,the first fruit node length of 1,2-10,9-12 and 10-12 fruit branches,the second fruit node length of 2,2-8,6-12 and 8-12 fruit branches,and the third fruit node length of 1,1-5,5-11 and 5-12 fruit branches were significantly affect,respectively.In addition,MC application at post-topping stage significantly affect the third fruit node length of 12 fruit branch.The length of the main stem internode and fruit node shortened more as MC rates increased.The quantitative effect of MC on plant type does not follow the "dose determination intensity",which is affected by climatic conditions and growth stages.The growth rate of cotton plants is faster when MC is used,the quantitative effect is more obvious.(2)Averaged over years,cultivars,and plant density,the results showed that the yield significantly increased by 5.6,5.0 and 6.1%because of MC application at the seedling,early bloom and full bloom stage,respectively.However,MC application at the squaring and post-topping stage did not significantly affect the yield.Year(mainly precipitation),cultivar,and plant density interacted with MC applied at certain specific growth stages.Plant density influenced yield response to early MC application at the seedling stage.At high density(11.4plant m-2),MC produced a 9.4%higher yield than control,whereas there was only a 1.8%increase at low density(6.4 plants m-2,).It may be the root growth at high density is enhanced more strongly than that at low density,so that the absorption capacity of cotton and the resistance of drought,water logging and other non-biological stress resistance was stronger.The interaction of the year by MC for yield occurred when MC was applied at the early bloom and full bloom stages.MC application at early bloom and full bloom stage resulted in 14.1 and 16.1%yield increase,respectively.However,MC application at the same time in 2014 caused only a slight increase or decrease in yield.This is mainly related to the excess rainfall in July 2013 and the drought in July 2014.Cultivars differed in yield responses to MC applied at the full bloom and post-topping stage.MC application at the full bloom and post-topping stages increased the yield of Han7860 11.9 and 13.2%,respectively,but almost had no effect on the yield of SCRC36(±2%).Because Han7860 had higher vegetative growth rate than SCRC36 in mid-and later growing season.(3)The relationship between cotton plant architecture and seed yield was analyzed statistically.The result showed that the yield was negatively correlated with the length of the first fruit node.The relationship was relatively stable under different years,varieties,densities,and MC.The linear fitting equation of the yield and the length of the first fruit node is y =-284.74x + 7393.5.Therefore,the length of the first fruit be not only used as a predictor index of cotton yield,but also as a basis forjudging the time and dose of MC application.Therefore,we recommend a strategy of MC application for cotton management in the Yellow River valley region of China.An early MC application of 3.75-7.5 g ha-1 at the seedling stage is needed,particularly at the high plant density.Then,a MC application of 22.5-45.0?g ha-1 at early bloom or 30.0-60.0 g ha-1 at full bloom stage should be followed to control excessive vegetative growth,especially in the year with heavy precipitation in July.Lastly,a late MC application of 45.0-90.0 g ha-1 at the post-topping stage is necessary for vigorous cotton cultivars to facilitate the balance of vegetative and reproductive growth.This strategy could make sure that the plant height is about 103 cm and the average length of fruit branches is about 27cm on the basis of ensuring yield,which could basically meet the requirements of mechanical harvesting.This strategy needs to be confirmed by more field researches and/or crop models. |
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