| Double cropping of wheat and cotton is an effective way to alleviate the contradiction between grain and cotton competing for land in Yellow River Basin.However,the traditional wheat-cotton double cropping system using full season cotton,requires to reserve a wide cotton interplanting rowin the wheat field,which leads to a long intergrowth period of wheat and cotton,low wheat yield,poor cotton crop maturity,and difficulty in mechanized cultivation and harvest.Short-season cotton with the characteristics of late sowing and early maturity,can be used in wheat-cotton double cropping system to shorten the intergrowth period,which is expected to solve the problems of low wheat yield,poor cotton crop maturity and unfavorable to mechanized harvest.In order to provide theoretical and technical guidance for the mechanized cultivation management of double-cropping wheat and cotton in the Yellow River Basin,the effects of the spatial-temporal allocation of crops on the growth and development,population structure characteristics and yield formation of short-season cotton were studied by setting different crop modes and sowing dates.There were two field experiments carried out in this study.In Experiment 1,the crop mode experiment was carried out.A full-season cotton variety ZM79 and a short-season cotton variety ZM50 were used.Three croping modes including W2C1(2 rows of wheat and 1 row of cotton),W3C 1(3 rows of wheat and 1 row of cotton)and W6C2(6 rows of wheat and 2 rows of cotton)were compared.The distribution and utilization of heat and light resources,crop yield and yield components,edge effect ofwheat and economic benefits were studied.In Experiment 2,the sowing date effects of short-season cotton were studied.The cotton variety ZM 50 was grown in W3C 1 crop mode with 4 sowing dates including May 15,May 25,June 5 and June 15 to investigate the effects of sowing date on cotton yield,dry matter accumulation and allocation,cotton boll spatial and temporal distribution and dry matter translocation.The main results and conclusions are as follows:1.The efficient allocation mode of wheat and short-season cotton under double cropping system was determined,and its mechanism of high yield and high efficiency was revealed1)The wheat yield in W3C1 cropping mode had obvious advantages.Wheat accounted for 65.8%of land area at maturity in W3C1,increased by 13.2 and 10.5 percent points compared with W2C1 and W6C2,respectively.The interception rate of photosynthetic active radiation(PAR)of wheat,the use efficiency of light and heat wereall higher in W3C1.The effective panicle number of wheat and grain yield in W3C1 were significantly higher than those in W3C1 and W6C2,in which the effective panicle number of wheatincreased by 16.6%and 36.5%,respectively,and the grain yield increased by 22.5%and 28.2%,respectively.In addition,although the edge effect ofW3C1 on grain yield and effective panicle number was lower than that of W6C2,it indicated that there was little difference between the middle rows and border rows of W3C 1,and the compensation ability of the middle rows in W3C1 was stronger than that in W6C2.2)The cropping mode of W3C1 produced comparative cotton yield to that of other crop modes,but its economic benefit was the highest.There was no significant difference in cotton yield and yield components among different crop modes of the same variety,but the land equivalent ratio(LER)was different,leading to different economic benefits.Compared with the crop mode of W6C2 for ZM50,the land equivalent ratio was significantly increased by 14.6%on average,the economic benefit was increased by 38.4%,the production benefit per unit working day was increased by 32.7%,and the production benefit per unit material was increased by 150.8%in the crop mode of W3C1forZM50.Under the crop of W3C1,compared with ZM79,the LER of ZM50 was significantly increased by 8.6%,and the economic benefit was improved by 88.7%.3)The ZM50 performed better than ZM79inW3C1.The growth process and cotton maturity significantly varied with cotton genotypes in W3C1.The boll opening date ofcotton in W3C1 was 18-32 days earlier for ZM50 than that for ZM79.By applying ZM 50,the seedling quality was improved during the intergrowth period,the plant height and the ratio of nodes to branches were reduced,the dry matter accumulation of reproductive organs was fast,the node position completed the accumulation of 50%yield was lower,and the pre-frost boll opening rate is above 82.1%.In addition,the cotton was grown in an equal row space of 76cm,which was suitable for mechanical harvest,and thus can greatly reduce the cost of cotton picking.2.The optimum sowing date of short-season cotton configured with wheat in 3-1 was determined,and the mechanism of early sowing to promote the centralized Boll-setting and yield increase of short-season cotton was revealed1)Sowing date significantly affected the growth and development of short-season cotton.The number of fruit branches and dry matter per plant in two early sowing treatments(May 15 and May 25)were significantly higher than those in the late sowing treatment(June 15),while the plant height and the ratio ofnodes to branches were higher in the treatments of May 25or June 5.The peak value of leaf area per plant appeared earlier and higher in early sowing treatments.The first main stem leaf from the top was fully extended at the end of July in early sowing treatments,which was 20-25 days earlier than that in the late sowing treatment of June 15.The SPAD values of 1-4 main stem leaves from the top were significantly higher in early sowing treatments than those in late sowing treatment.The initial date of dry matter fast growth period was delayed with the delay of the sowing date,and the growth rate of early sowing was higher than that of late sowing.The duration of rapid growth of reproductive organs in early sowing treatment was 7.8-8.7 days longer than that in late sowing,and the total dry matter was 13.3-29.9%higher than that in late sowing.2)Sowing date significantly affected the yield and fiber quality of short-season cotton.The harvest index,lint percentage,average boll weight and the weight of the first fruitingboll all decreased with the delay of sowing date.Lint yield and seed cotton yieldin the first three sowing dates were significantly higher than those on June 15,and the early sowing(May 15)increased cotton yield by 28.1-31.5%compared with the late sowing(June 15).The later the sowing date,the greater the risk of yield reduction,because the drop of boll weight increases with the delayed sowing date.The proportion of young boll shedding in the sowing treatments of May 15 and May 25 was 23.1 to 25.7%lower than that in the treatments of June 15 and June 5,indicating that the early sowing treatments had less loss of photosynthetic products due to organ shedding and was beneficial for harvest index increase.Similarly,with the delay of sowing date,the pre-frost flowering rate decreased,and late sowing reduced the pre-frost flowering rate by 20.4-42.9%.There was no significant difference in fiber quality of pre-frost bolls among different sowing treatments,but there was a large proportion of post-frost bollswith poor fiber quality.3)The early sowing of cotton improved cotton yield was mainly due to the concentrated boll distribution and increased internal bolls.In the spatial distribution of boll weight and boll retention rate,the area with high boll retention rate(boll retention rate>0.3)was distributed at the 1st and 2nd fruiting sites(mainly 1st fruiting site)of the fruiting branches from 2nd to 9th;However,the area with high boll retention rate in late sowing cotton(June 15)mainly distributed at the 1st to 3rd fruiting sites of the fruiting branches from 2nd to 5th.The number of first fruiting bolls in early sowing treatment was 27.2-49.0%more than that in late sowing treatment.In addition,the contribution rate of the first fruiting bolls to seed cotton yield was increased by 22.5-23.1%compared with that in late sowing.The dominant(greater than average boll weight)area of boll weight of early sowing treatment moved up and expanded compared with the dominant(greater than average boll-setting rate)area of boll setting,while the dominant area of boll weight overlapped with the dominant area of boll retention rate in the late sowing treatment,indicating that early sowing increased boll weight on the basis of guaranteeing the number of bolls,which optimized the boll distribution and was beneficial to mechanical harvest.4)The reduction in the boll weight in the late sowing treatment was due to the insufficient source and sink.It was found that the dry matter allocation ratio to the reproductive organs in the late sowing treatment was decreased by 6.0-12.4%compared with that in the early sowing treatment.Also,compared with the early sowing treatment,the dry matter allocation ratio to the reproductive organs in the lower,middle and upper branches in the late sowing treatment also decreased,resulting in reductions of 1.8-1 5.1%,4.8-14.1%and 9.4-26.5%in the dry matter of cotton bolls in lower,middle and upper branches,respectively.On the other hand,in the redistribution of dry matter in cotton bolls,the boll shell coefficient of the late sowing treatment was 0.418-0.478,which was 8.7-12.4%higher than that of the early sowing treatment.The dry matter transfer rates related to lower,middle and upper branches of the late sowing treatment were lower than that of the early sowing treatment.It showed that the dry matter transport volume in the fluid is low,that is,the flow is weak.The boll weight of three branches decreased by 4.1-19.5%,26.5-27.6%and 11.1-27.5%,respectively.In conclusion,the cropping mode of W3C1 in short-season cotton and wheat double cropping system is a high-efficient crop mode.It increases the effective spike number and enhances the compensation effect of the middle rows of wheat,resulting in higher LER and economic benefits.Moreover,the crop mode of W3C 1 was suitable for mechanical harvest,and thus greatly reduced the cost for cotton harvest.Under the mode of W3C1,short-season cotton seeded from May 15 to 25 increased cotton yield and the crop maturity,compared with that that seeded on June 15,which could be attributed to the long duration of the fast growth period of dry matter of reproductive organs,and high allocation ratio to reproductive organs,low ratio of boll shell to bolland high yield contribution rate of inner bolls.In short,a new mode of wheat-cotton double cropping feasible for mechanical harvest was established in the paper,adopting the crop mode of W3C1 and sowing short-season cotton 20-30 days before wheat harvest.The physiological and ecological mechanism of high yielding and high efficiency of the new moed was also revealed.This research provides theoretical and technical support forthe development of wheat-cotton double cropping in the Yellow River Basin of China. |
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