Shulin WANG，Hong Ql，Yan WANG，Qian ZHANG，Guoyi FENG，Yongzeng LlN，Qinglong LlANG

Cotton Research Institute，Hebei Academy of Agricultural and Forestry Sciences/Key Laboratory of Biology and Genetic Improvement of Cotton in Huanghuaihai Semiarid Area，Ministry of Agriculture，Shijiazhuang 050051，China

Effects of Sowing Rate on Marginal Superiority and Yield of Wheat in Wheat-cotton lntercropping System

Shulin WANG，Hong Ql，Yan WANG，Qian ZHANG，Guoyi FENG，Yongzeng LlN*，Qinglong LlANG

Cotton Research Institute，Hebei Academy of Agricultural and Forestry Sciences/Key Laboratory of Biology and Genetic Improvement of Cotton in Huanghuaihai Semiarid Area，Ministry of Agriculture，Shijiazhuang 050051，China

In the wheat-cotton intercropping system，total 6 sowing rates （187.5，225.0，262.5，300.0，337.5 and 375.0 kg/hm2）were arranged，and the effects of sowing rate on marginal superiority and yield of wheat were investigated.The results showed that the effect of sowing rate on inner-line wheat was greater than that on side-line wheat；with the increased sowing rate，the marginal superiority of panicle number was reduced in overall，and the difference in panicle number between inner and side lines was decreased from 9.0×105/hm2（sowing rate of 187.5 kg/hm2）to 7.8×105/hm2（sowing rate of 375.0 kg/hm2）；the marginal superiority of grains per spike was increased first and then reduced，and the largest difference in grains per spike between the inner and side lines reached 4.6 under the sowing rate of 300.0 kg/hm2；the marginal superiority of 1 000-grain weight and yield was gradually increased，and the largest difference in 1 000-grain weight between the inner and side lines reached 3.9 g under the sowing rate of 337.5 kg/hm2，and in yield reached 3 136.5 kg/hm2under the sowing rate of 375.0 kg/hm2.The effects of sowing rate on the three yield factors of intercropped wheat ranked as panicle number＞grains per spike＞1 000-grain weight.The appropriate sowing rate of wheat was 225.0-262.0 kg/hm2in the wheat-cotton intercropping system.

Wheat-cotton intercropping；Wheat；Sowing rate；Marginal superiority；Yield

W heat-cotton double cropping pattern first appeared in the Yangtze River Basin in the 1950s.In the cultivation system，the wheat was winter wheat（Yuanmai），and the cotton was sowed directly［1］.In the 1960s，the double cropping pattern was introduced to the cotton-growing region in the Huanghe River Basin，where the cotton was mainly inter cropped with wheat［2］.The double cropping pattern became the main farming mode in the Huanghe River Basin in the late 1990s［3］.However，with the promoting of wheat harvester，the wheat-cotton intercropping area was reduced rapidly.Therefore，since the early 2000s，the researches on wheat-cotton intercropping technology began to focus on basic theory，such as effect of soil ecosystem［4-5］in the intercropping system on root growth of cotton［6］.However，there were rare reports on application of wheat-cotton intercropping system.In recent years，with the growing concern over food safety issues and increasingly intense competition between wheat and cotton for arable land，wheat-cotton intercropping system attracts more and more attention.After wheat harvester became applicable to wheat-cotton intercropping system，wheat-cotton intercropping system has great promotion prospects.In the wheat-cotton intercropping system，to ensure high yield of wheat，the sowing rate of wheat is generally increased.However，excessive sowing rate will also increase potential lodging risk of wheat.Therefore，in this study，the effects of sowing rate on marginal superiority and yield of wheat were investigated in the wheat-cotton intercropping system，thereby providing experimental basis for determination of appropriate sowing rate of wheat.

Material and Methods

Test site and material

The test was carried out in the Quzhou experimental station（Xizhangtou Village，Quzhou County，Handan City，Hebei Province）of Cotton Research Institute，Hebei Academy of Agricultural and Forestry Sciences.The last-season crop was cotton.The soil was clay loam with medium fertility.In the clay loam，the contents of organic matter，total nitrogen，available phosphorus and available potassium were 14.6，0.998 g/kg，38.9 and 285.8 mg/kg，respectively.The wheat cultivar was Xingmai No.4.

Test design and methods

The randomized block design was adopted.Total 6 sowing rates of wheat were designed，including 187.5，225.0，262.5，300.0，337.5 and 375.0 kg/hm2. There were three replicates for each treatment.The size of each plot was 6.4 （W）×8.0 （L）m.In each plot，4 lines （width of each line of 80 cm）of wheat were intercropped with 2 lines（width of each line of 80 cm）of cotton. Along with tillage，a certain amount（750 kg/hm2）of N-P-K（18∶16∶7）compound fertilizer was applied on November 4，2013.The seeds were sowed and watered on November 6. On March 11，2014，the wheat seedlings were watered，and a certain amountofnitrogen fertilizer（225 kg/hm2）was applied.The other management measures were the same with those in general fields.The wheat was harvested on June 9，2014.

During the harvest，3 sampling points were designed for each plot.In each sampling point，certain lengths（1 m）of inner-line wheat（two middle lines among the four lines）and sideline wheat（two marginal lines among the four lines）were sampled for determination of panicle number.Among the sampled spikes from each plot，total 50 spikes were selected randomly for determination of grains per spike and 1 000-grain weight.The wheat in each plot was harvested singly.

Data statistics and analysis

The data were processed using Excel 2003，and the variance analysis was conducted using DPS7.05.

Table 1 Panicle numbers of wheat under different sowing rates 104/hm2

Table 2 Grains per spike of wheat under different sowing rates

Results and Analysis

Effect of sowing rate on panicle number of wheat

Table 1 showed that with the increase of sowing rate，the panicles numbers of side and inner lines were alltrended to be increased.The largest difference in panicle number of side line among different sowing rates reached 3.075×106/hm2，and in panicle number of inner line reached 3.195× 106/hm2.It indicates that the effect of sowing rate on panicle number of inner line is greater than that on panicle number of side line.Under different sowing rates，the panicle numbers of side lines were all higher than those of inner lines，indicating obvious marginal superiority.With the increased sowing rate，the difference in panicle number between side and inner lines became small.It suggests that the lower the sowing rate is，the fewer the panicles are，and the fewer the panicles are，the more obvious the marginal superiority is.With the increased sowing rate，the average panicle number was increased significantly，and the panicle number at the sowing rate of 375.0 kg/hm2was 72.6%higher than that at the sowing rate of 187.5 kg/hm2.

Effect of sowing rate on grains per spike of wheat

As shown in Table 2，with the increase of sowing rate，the grain number per spike of side and inner lines were all trended to be decreased.The largest difference in grains per spike of side line among different sowing rates reached 7.1，and in grains per spike of inner line reached 8.9.It indicates that the effect of sowing rate on grains per spike of inner line was greater than that on grains per spike of side line. Underdifferentsowing rates，the grains per spike of side lines were all higher than those of inner lines，indicating obvious marginal superiority in side lines.With the increased sowing rate，the difference in grains per spike between side and inner lines was increased first and then decreased.The marginal superiority was greatest（difference in grains per spike of 4.6）at the sowing rate of 300.0 kg/hm2.It suggests that too high or too low sowing rate is all adverse to marginal superiority.With the increase of sowing rate，the average grain number per spike was reduced gradually，and the grains per spike at the sowing rate of 187.5 kg/hm2was 30.7%higher than that at the sowing rate of 375.0 kg/hm2.

Effect of sowing rate on 1 000-grain weight of wheat

The 1 000-grain weights of both side and inner lines were all reduced with the increase of sowing rate.The largest difference in 1 000-grain weight of side line among different sowing rates was 3.8 g，and in 1 000-grain weight of inner line was 4.5 g，indicating greater effect of sowing rate on inner line than that on side line.Underdifferent sowing rates，the 1 000-grain weights of side lines were all higher than those of inner lines，indicating obvious marginal superiority.With the increased sowing rate，the difference in 1 000-grain weight between side and inner lines was increased in overall.The higher the sowing rate was，the more obvious the marginal superiority of 1 000-grain weight was.The average 1 000-grain weight was decreased with the increase of sowing rate，and the 1 000-grain weight at the sowing rate of 187.5 kg/hm2was 4.2 g（9.9%）higher than that at the sowing rate of 375.0 kg/hm2.

Table 3 1 000-grain weights of wheat under different sowing rates g

Table 4 Yields of wheat under different sowing rates kg/hm2

Effect of sowing rate on yield of wheat

Table 4 showed that the yields of side and inner liens were increased first and then decreased with the increase of sowing rate.The sowing rate of 225.0 kg/hm2showed the highest yield of wheat.The largest difference in yield of side line among different sowing rates was 465.0 kg/hm2，and in yield of inner line was 1 275.0 kg/hm2，indicating greater effect of sowing rate on inner line than that on side line. With the increase of sowing rate，the yield difference between side and inner lines was increased in overall.At the sowing rate of 375.0 kg/hm2，the yield difference between side and inner lines was 3 136.5 kg/hm2，which was 810.0 kg/hm2higher than that at the sowing rate of 225.0 kg/hm2.The higher the sowing rate was，the more obvious the marginal superiority of wheat yield was.The average yield of wheat was increased first and then decreased with the increase of sowing rate.The wheat yield was highest（6 893.3 kg/hm2）at the sowing rate of 225.0 kg/hm2，but was lowest at the sowing rate of 375.0 kg/hm2.There were no significantdifferences in wheat yield among the three sowing ratesof187.5，225.0and262.5 kg/hm2.

Conclusions and Discussion

The researches on appropriate sowing rate of wheat mostly focus on single cropping wheat.Yang et al.［7］found that with the increase of sowing rate，the basic seedlings and highest tiller number were increased；the tiller number per plant and 1 000-grain weight were decreased；the yield was increased first and then decreased.Li et al.［8］considered that different sowing rate showed great effect on yield. When the sowing rate was increased，the lodged wheat plants were increased at the late growth period，resulting in decreased yield.With the increase of sowing rate，the heading rate was increased，but the 1 000-grain weight was reduced.The study results of An et al.［9］showed that sowing rate had certain regulation effect on wheat population，but the effect of sowing period on wheat yield was greater.Wu et al.［10］found that with the increased sowing rate，the yield was increased first and then decreased，the effective panicles were increased，and the panicle length，grains per spike and 1 000-grain weight were all reduced.Luo et al.［11］found that sowing rate had significant effect on yield.Too high sowing rate significantly reduced yield.With the increased sowing rate，the heading rate was increased，and the grains per spike and 1 000-grain weight were increased first and then decreased.The results of this study showed that with the increase of sowing rate，the grains per spike of wheat was increased，which was consistent with previous study results in single cropping system.The grains per spike and 1 000-grain weight were decreased gradually with the increased sowing rate，which was consistent with the study results of Yang et al.［7］，Li et al.［8］and Wu et al［10］.However，Luo et al.［11］considered that with the increase of sowing rate，the grains per spike and 1 000-grain weight showed a parabola change tendency，which might be caused by fewersowing ratetreatmentsand smaller gradient between two adjacent sowing rates.The wheat yield was increased first and then decreased with the increase of sowing rate，which was consistent with the finding of Li et al［8］. This study found that the appropriate sowing rate of wheat was 225.0-262.5 kg/hm2.

There have been many reports on marginal superiority of wheat，but the conclusions are different.Zhao et al.［12］considered that there was a close correlation between wheat cultivar and marginal superiority.Under the condition of narrower reserved lines，the marginal superiority of wheat cultivar with dwarf plants，stronger tillering ability and more but smaller spikelets would be better played，resulting in higher yield.When the reserved lines were wider，the marginal superiority of wheat cultivar with moderate type or large-spike type would be fully played，resulting in higher yield.In terms of contributions of marginal superiorities of three yield factors on wheat yield，An et al.［13］found that the yield of sideline wheat was higher than that of inner-line wheat due to higher panicle number and 1 000-grain weight；but Yang et al.［14］considered that the wheat-cotton intercropping specification showed great effect on panicle number per unit area，instead of grainsper spike and 1 000-grain weight of wheat.Previous studies mostly focused on effect of wheat cultivar on marginal superiority.There are rare reports on effect of sowing rate of wheat on marginal superiority.In this study，the effect of sowing rate on marginal superiority of wheat was investigated.The results showed that the effects of sowing rate on panicle number，grains per spike，1 000-grain weight and yield of inner-line wheat were greater than those of side-line wheat；there was obvious marginal superiority in panicle number，grains per spike and 1 000-grain weight of wheat under different sowing rates；with the increase of sowing rate，the marginal superiority of panicle number was reduced，but of grains per spike was increased first and then decreased；at the sowing rate of 300.0 kg/hm2，the marginal superiority was highest；the marginal superiorities of 1 000-grain weight and yield of wheat were all increased with increase of sowing rate；considering effects of sowing rate on three yield factors of wheat，panicle number was greatest affected，followed by grains per spike，and the effect of sowing rate on 1 000-grain weight was weakest.

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Responsible editor：Tingting XU

Responsible proofreader：Xiaoyan WU

麥棉套作模式下播量對小麥邊行優(yōu)勢與產(chǎn)量的影響

王樹林，祁虹，王燕，張謙，馮國藝，林永增*，梁青龍 （河北省農(nóng)林科學院棉花研究所/農(nóng)業(yè)部黃淮海半干旱區(qū)棉花生物學與遺傳育種重點實驗室，河北石家莊050051）

在麥棉套作模式下，設置了187.5、225.0、262.5、300.0、337.5、375.0 kg/hm26個小麥播量處理，研究了不同播量對小麥邊行優(yōu)勢與產(chǎn)量的影響。結(jié)果表明，播量對內(nèi)行小麥的影響大于邊行，隨著播種量的增加，穗數(shù)的邊行優(yōu)勢總體降低，邊行與內(nèi)行差值由90萬穗/hm2（播量187.5 kg/hm2）降至78.0萬穗/hm2（播量375.0 kg/hm2）；穗粒數(shù)邊行優(yōu)勢總體先增后減，播量300.0 kg/hm2處理邊行與內(nèi)行穗粒數(shù)差值最高（4.6粒）；千粒質(zhì)量與產(chǎn)量邊行優(yōu)勢總體逐漸增加，播量337.5 kg/hm2處理邊行與內(nèi)行千粒質(zhì)量差異最高（3.9 g），產(chǎn)量邊行與內(nèi)行差值以播量375.0 kg/hm2處理最高，為3 136.5 kg/hm2；播量對套作小麥產(chǎn)量三因素影響的大小依次為穗數(shù)、穗粒數(shù)、千粒質(zhì)量，麥棉套作小麥適宜播種量在225.0～262.0 kg/hm2。

麥棉套作；小麥；播量；邊行優(yōu)勢；產(chǎn)量

國家科技支撐計劃項目（2013BAD05B00）。

王樹林（1978-），男，河北巨鹿人，副研究員，主要從事棉花栽培與麥棉兩熟雙高產(chǎn)栽培技術(shù)研究，E-mail：wshl1001@sohu.com。

2015-09-02

SupportedbyNationalKeyTechnologyResearchandDevelopmentProgram（2013BAD05B00）.

*Corresponding author.E-mail:zaipei@sohu.com

Received:September 2，2015 Accepted:November 1，2015

*通訊作者，研究員，主要從事棉花栽培及生理生態(tài)研究，E-mail：zaipei@sohu.com。

修回日期 2015-11-01