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Abstract [Objective]This study was conducted to investigate the relationship between each of planting density and row spacing and plant productivity of forage sweet sorghum planted in autumn idle land. [Methods]Using splitplot experiment design experiment method and LSD method of IBM.SPSS.Statistics.v22 statistics software， the effects of planting density and row spacing on plant productivity of forage sweet sorghum planted in autumn idle land were compared. [Result]The results showed that the planting density and row spacing had important influences on plant productivity of forage sweet sorghum planted in autumn idle land. Moreover， the optimal combination of plant productivity for A1B4， i.e.，under the combination of the planting density of 7.5×104 plants/hm2 and the row spacing of 40 cm， the fresh weight and dry weight per plant were 654.37 and 147.11 g/plant， respectively.[Conclusion] The results provided a theoretical basis for the production of forage sweet sorghum in autumn idle land.
Key words Autumnidle land； Forage sweet sorghum； Planting density； Row spacing； Plant productivity
Received： August 19， 2017 Accepted： October 29， 2017
Supported bySpecial Fund for Agroscientific Researchin the Public Interest （20120304201）.
Hanzhang ZHOU（1960-）， male， P. R. China， researcher， devoted to research about plant protection and cultivation technology of annual fodder crops， Email： [email protected].
*Corresponding author. Email： [email protected]； Email： [email protected]
Sweet sorghum[Sorghum bicolor （L.）Moench] is a crop in Sorghum of Gramineae family， which serves as a forage， sugar and energy crop. Sweet sorghum as an important common forage crop， has the characteristics of high drought resistance， strong tolerance to waterlogging， lower fertility and salinealkaline soil， and strong reproducing property[1-2]. The plant is high with lush stems and leaves， rich in sugar， and has good palatability. It could be fed after ensiling， or prepared into grass meal or other grass products[3-4]， mainly silage. Planting forage sweet sorghum in autumn idle field could take full advantage of natural resources including light， air， heat， water， soil and fertilizer and improve the cropping index of land， and is thus of great significance to the improvement of farmers income and the promotion of rapid， sustainable and stable development of feeding sweet sorghum industry and animal husbandry.
The plant productivity of forage sweet sorghum is composed of the weights of the stem， leaves and ear， as well as an important factor affecting the biological yield of sorghum. Planting density and row spacing are effective measures for the regulation of the contradictory between plant growth and population growth. The research on the relationship between each of planting density and row spacing and plant productivity is of great significance to the investigation of the variety of forage sweet sorghum planted in autumn idle field and its high yield technique. There are many studies on plant productivity. Sheng et al.[5]studied the plant density of sparselyplanted seedlings raised on fertilized dryland bed in rice. Xu et al.[6] clearly defined the technique of plant productivity of millet. Yan et al.[7]investigated the relationship between plant productivity and density of wheat. Guo et al.[8] performed correlation analysis between main agronomic traits and plant productivity with a new peanut variety as study object. Yang et al.[9]deemed that the increase of planting density would reduce the plant productivity of wheat. Currently， there were no studies on the plant productivity of forage sweet sorghum cultivated in autumn idle field. In this study， with Sorghum bicolor cv. Nengsi No.1 as a tested crop， the optimal combination of planting density and row spacing and corresponding effect on plant productivity of forage sweet sorghum were investigated， so as to provide data basis and technical support for the highyield highefficiency cultivation technique of forage sweet sorghum in autumn idle field. Materials and Methods
Experimental materials
The tested cultivar was Sorghum bicolorcv. Nengsi No.1 （provided byInstitute of Millet Crops，Hebei Academy of Agriculture and Forestry Sciences/Hebei Branch Center of National Sorghum Improvement Center）.
General situation of experiment field
The experiment was carried out in Dongke Village， Luancheng District， Shijiazhuang City. The village is located at 37°58′32″ northern latitude，114°36′33″ east longitude， with an altitude of 56 m. The experimental field is flat with convenient drainage and irrigation. The soil has a proper soil moisture content with medium fertility. The soil is loam， with a soil organic matter of 1.73%， a total nitrogen content of 1.12 g/kg， a alkalihydrolyzale nitrogen content of 79.5 mg/kg， a rapidly available phosphorus content of 22.3 mg/kg and a rapidly available potassium content of 113.9 mg/kg， and the soil has a pH value of 7.2.
Experimental methods
Experimental design
Twofactor split plot experimental design was adopted[10-11]. The main plot treatments were about the density of reserved seedlings， which was designed with four levels， i.e.， 75 000， 225 000， 375 000 and 525 300 plants/hm2， which were represented by A1， A2， A3 and A4， respectively. The subplot treatments were about row placing， which was designed with six levels， i.e.， 10， 20， 30， 40， 50 and 60 cm， which were represented by B1， B2， B3， B4， B5 and B6， respectively. The main plots and subplots were all in random arrangement， with three replicates， and there were 72 plots in total. Each subplot had an area of 20 m2 （4 m×5 m）， and an observation way with a width of 1.0 m was reserved between two subplots. A protection region with a width of 1 m was reserved around the experimental field.
The previous crop was oil sunflower， which was harvested on July 26. July 28 was cloudy with showers， July 29 encountered moderate rain， and shower happened fromJuly 30 in the night of to July 31 in the night. Ploughing was performed on August 3-4， and seeding was performed on August 7.Artificial sowing in drill was adopted with a seeding depth of 3-4 cm， and the sown seeds were covered uniformly and then stepped on. Thinning was performed during the period of 2-3 leaves， and the final singling was performed during the period of 4-6 leaves. No base fertilizer was applied before seeding， and topdressing was not performed after seeding.
Determination items and methods The rice was cut on October 28. Three rows were selected from each plot， and 10 plants were continuously cut and mixed uniformly. Then， 10 plants were randomly selected from each plot and labeled （to give clear indication of species， treatment number， and cutting and sampling time）.The plants were weighed and airdried to a water content of 13%-15%， and the dry weight was then measured， so as to calculate the productivity of single plant. The productivity of single plant was represented by fresh weight or dry weight of single plant.
Data processing and analysis
The experimental data was processed with Microsoft Excel 2010. Statistical analysis and plotting were performed in IBM.SPSS.Statistics.v22. Each block （replicate） was analyzed as one factor. The variance analysis of the main plot and subplot factors should select different error terms， and Eb=MS（R（A）） and Ec=MS（e） were used as the error terms for the test of main plot factor （Ai） and subplot factor （Bj）， respectively. Multiple comparisons were then performed by LSD method[10， 12-13]. All the statistical results were represented by "mean ± SD".
Results and Analysis
Effects of various treatments on the productivity of single sweet sorghum plant
Table 1 showed the fresh weight and dry weight per plant of Nengsi 1 under various treatments. The data showed that with the planting density increasing， the plant productivity decreased linearly； and with the row spacing increasing， the plant productivity exhibited a parabolic trend. Variance analysis （Table 2） showed that for different blocks （replicates）， the fresh weight and dry weight per plant exhibited F values of （Sig. of 0.455（Sig.=0.655， i.e.， P>0.05） and 2.923 （Sig.=0.130>0.05）， respectively，i.e.， there were significant differences， indicating that there were no big differences between blocks （replicates）， and the fertility was uniform， thereby reducing the error caused by nonuniform fertility. For the main plottreatments （planting density）， the fresh weight and dry weight per plant had F values of 1 770.86 and 1 918.028， respectively， and the significant values （Sig.） were all 0.000<0.01， i.e.， the differences between treatments were very significant， indicating that different planting densities greatly affected the plant productivity of Nengsi 1； for the subplot treatments （row placing）， the fresh weight and dry weight per plant showed F values （Sig.） of 2.373 （Sig.=0.056>0.05） and 4.781 （Sig.=0.002<0.01）， respectively， i.e.， there were no significant differences in the fresh weight per plant， but the dry weight per plant differed significantly， indicating that row spacing had certain effect on the plant productivity of Nengsi 1. As to the planting density and row spacing interaction， the fresh weight and dry weight per plant showed the F values （Sig.） of 0.491（Sig.= 0.811>0.05） and 1.259 （Sig.=0.272>0.05）， i.e.， there were no significant differences， indicating that the planting density did not interact with row spacing， i.e.， the effect of planting density did not change with the change of row spacing， and the effect of row planting also did not change with the change of planting density. Effect of different planting densities on the productivity of single sweet sorghum plant
It could be seen from Table 3 that with the planting density of Nengsi 1 increasing from 75 000/hm2 to 525 300 plants/hm2， the fresh weight per plant decreased from 602.74 to 79.73 g/plant， and the dry weight per plant decreased from 135.90 to 18.25 g/plant. The differences reached the very significant level， indicating that the planting density had a significant effect on the productivity of single plant. Nengsi 1 had the highest productivity under the planting density of 75 000/hm2 （Fig. 1）. Under the planting density of 75 000/hm2， its fresh weight per plant （602.74 g/plant） increased by 42.41%-86.77% compared with other planting densities， and its dry weight per plant （135.90 g/plant） increased by 41.79%-86.58% compared with other planting density， exhibiting very significant differences. The planting density， 225 000 plants/hm2 produced a middle productivity. Under the planting density of 225 000 plants/hm2， the fresh weight and dry weight per plant were 347.12 and 79.11 g/plant， respectively. The fresh weight per plant decreased by 73.64% compared with the planting density of 75 000/hm2， but increased by 48.35% and 77.03% compared with the planting densities of 375 000 and 525 300 plants/hm2， respectively， with very significant differences. The dry weight per plant decreased by 71.79% compared with the planting density of 75 000/hm2，but increased by 49.74% and 76.94% compared with the planting densities of 375 000 and 525 300 plants/hm2， respectively， with very significant differences.Under the planting density of 525 300 plants/hm2， the productivity was the lowest. Specificity， the fresh weight and dry weight per plant were 79.73 and 18.25 g/plant， respectively， and compared with fresh weight and dry weights under other planting densities， the value decreased remarkably， with very significant differences. The results showed that with the planting density increasing， the population competitiveness of Nengsi 1 increased， which inhibited the yield increasing potential of single sweet sorghum plant， resulting in reduced plant productivity.
Table 1 Results of plant productivityunder different planting density and row spacing treatments
Density∥104plants/hm2Row spacing ∥cm
Fresh weight∥g/plant
IIIIIIMean
Dry weight∥g/plant
IIIIIIMean
A17.5
A222.5
A337.5
A452.5
B110560.60586.50595.10580.73124.01125.93119.67123.20 B220596.90576.50596.00589.80117.87140.60139.00132.49
B330599.90606.50619.60608.67146.53142.53147.00145.35
B440666.80659.50636.80654.37152.00155.00134.33147.11
B550591.60601.70608.20600.50144.93135.40134.40138.24
B660595.10564.40587.60582.37122.00127.00138.07129.02
Mean601.82599.18607.22602.74134.56137.74135.41135.90
B110365.10345.60135.60282.1071.2079.4935.2661.98
B220368.60346.00362.80359.1379.2481.3174.3878.31
B330342.10368.80375.10362.0076.9884.0082.5181.16
B440351.00369.60382.80367.8087.7683.1691.8787.60
B550338.10358.40378.80358.4377.7682.4289.0283.07
B660334.00357.00368.80353.2786.8580.3380.4782.55
Mean 349.82357.57333.98347.1279.9781.7975.5979.11
B110207.10151.60182.80180.5048.6731.8441.1340.55
B220211.10160.50173.80181.8047.4933.7136.4939.23
B330200.00169.80178.90182.9047.0039.9138.4741.79
B440186.00175.50193.50185.0039.0543.8841.6041.51
B550166.10169.30184.80173.4037.3741.4836.9638.60
B660161.80171.10183.80172.2336.4040.2134.0036.87
Mean188.68166.30182.93179.3142.6638.5138.1139.76
B11051.2063.50105.6073.4312.2914.2917.7614.78
B22063.1061.20105.0076.4314.2014.0823.6317.30
B330102.5082.1061.9082.1724.6018.8913.3018.93
B440103.1086.4072.2087.2327.8419.8815.5221.08
B55086.3097.6063.2082.3722.4422.9312.9419.44
B66093.2081.5055.5076.7322.0919.5612.2117.95
Mean83.2378.7277.2379.7320.5818.2715.8918.25
Agricultural Biotechnology2018
Table 2 Variance analysis of the effects of different planting densities and row spacing on plant productivity （intersubject simple effect test）
Determined index Source of variation III type of squares dfMean square FSig.
Fresh weight Replicate 483.3872241.6930.4550.655
Density 2 824 894.1103941 631.371 770.860.000
Error 3 190.4216531.737b
Row spacing 12 859.47252 571.8942.3730.056
Density*row spacing 3 190.4216531.7370.4910.811
Error 43 345.446401 083.636c
Dry weight Replicate 146.433273.2162.9230.130
Density 144 126.820348 042.2731 918.0280.000
Error 150.286625.048b
Row spacing 1 473.3935294.6794.7810.002
Density* row spacing 1 163.6821577.5791.2590.272
Error 2 465.3174061.633c
b. MS（replicate （density））， c. MS（error）.
Table 3 Productivity of single sweet sorghum plant under different plant density and its comparison results TermsDensity of reservedseedlings104 plants/hm2Weight of singleplant∥g
7.50∥104 plants/hm2
（increase/decrease）（±%）
22.50∥104 plants/hm2
（increase/decrease）（±%）
37.50∥104 plants/hm2
（increase/decrease）（±%）
52.53∥104 plants/hm2
（increase/decrease）（±%）
Fresh weight7.50602.74±28.25 aA-255.62*-73.64-423.43*-236.15-523.01*-655.98
22.50347.12±54.66 bB255.62*42.41-167.82*-93.59-267.39*-335.36
37.50179.31±16.13 cC423.43*70.25167.82*48.35-99.58*-124.89
52.5379.73±18.63 dD523.01*86.77267.39*77.0399.58*55.53
Dry weight7.50135.9±11.19 aA-56.79 *-71.79-96.15*-241.81-117.66*-644.69
22.5079.11±12.08 bB56.79 *41.79-39.35*-98.98-60.86*-333.50
37.5039.76±4.77 cC96.15*70.7539.35*49.74-21.52*-117.87
52.5318.25±4.86 dD117.66*86.5860.86*76.9421.51*54.1
（1） In the same column， different lowercase and uppercase letters indicate differences significant at 0.05 and 0.01 levels， respectively. （2） *indicates the significant level of the differences of means at 0.05. Similarly hereinafter.
Fig. 1 Effects of different planting densities on plant productivity of forage sweet sorghum
Effects of different row placing on the productivity of single sweet sorghum plant
It could be seen from Table 4 that the row spacing had an important effect on the productivity of single sweet sorghum plant. The row placing of 40 cm gave the highest productivity of single plant. The fresh weight per plant （323.60 g/plant） increased by 4.53%-13.72% compared with other row spacing， with nonsignificant differences from those under the row spacing of 20， 30 and 50 cm， but significant differences from those under the row spacing of 10 and 60 cm. The dry weight per plant （74.32 g/plant） increased by 3.38%-19.09% compared with other row spacing， with nonsignificant differences from those under the row spacing of 30 and 50 cm， but significant differences from those under the row spacing of 20 and 60 cm and a very significant difference from that under the row spacing of 10 cm. The row spacing of 30 cm gave the highest productivity of single plant. Specifically， the fresh weight per plant （308.93 g/plant） was not significantly different from those under the row spacing of 20 and 50 cm， but significantly different from those under the row spacing of 10 and 60 cm； and the dry weight per plant （71.81 g/plant） had a very significantly difference from that under the row spacing of 10 cm， but was not significantly different from those under other row spacing. The plant productivity was the lowest under the row spacing of 10 cm. Under the row spacing， the fresh weight and dry weigh per plant were， respectively，279.19 and 60.13 g/plant， which were remarkably lower than those under other row spacing. Under the experimental conditions， the row spacing of 30-50 cm is suitable， and 40 cm is the most suitable row spacing （Fig. 2）. Fig. 2 Effects of different row spacing on plant productivity of forage sweet sorghum
Table 4 Effects of different row spacing on the productivity of single sweet sorghum plant
Row spacingcm
Fresh weight
g/plant%
Dry weight
g/plant%
10279.19±59.37 bB13.7260.13±12.48 cB19.09
20301.79±58.87 abAB6.74 66.83±13.34 bAB10.08
30308.93±60.43 aAB4.53 71.81±14.49 abA3.38
40323.60±65.19 aA-74.32±14.70 aA-
50303.68±59.86 abAB6.16 69.84±13.85 abA6.03
60296.15±58.27 bAB8.48 66.60±13.04 bcAB10.39
Effects of different treatment combinations on the productivity of single sweet sorghum plant
It could be seen from Table 5 that the productivity of Nengsi 1 differed among the 24 treatments. Among the various treatments， treatment A1B4 showed the highest plant productivity， and the fresh weight per plant （654.37 g/plant） was not significantly different from that of A1B3， but significantly different from those of other treatments； and the dry weight per plant （147.11 g/plant） was not significantly different from those of treatments A1B3 and A1B5， but significantly from that of treatment A1B2 and very signifi cantly different from those of other treatments. Treatments A1B3 and A1B5 exhibited higher plant productivity. The two treatments showed the fresh weights per plant over 600.00 g/plant， and the dry weights per plant over 138.00 g/plant. The fresh weights and dry weights were not significantly different those of treatments A1B2 and A1B6， but very significantly different from those of other treatments. Treatment A4B1 exhibited the lowest plant productivity. Its fresh weight and dry weigh per plant were 73.43 and 14.78 g/plant， respectively. This treatment was not significantly different from treatments A4B2， A4B3， A4B4， A4B5 and A4B6 in both the fresh weight and dry weight per plant. The results showed that the treatment combinations have important effects on the productivity of single sweet sorghum plant， and treatments A1B3， A1B4 and A1B5 are optimized combination capable of giving play to the yield increasing potential of Nengsi 1， while treatment A1B4 is the optimal combination （Fig. 3）.
Table 5 Effects of different treatments on the productivity of single sweet sorghum plant
Treatment combination
Density∥104 plants/hm2Row spacing∥cmFresh weight∥g/plantDry weight∥g/plant
A17.50
A222.50
A337.50
A452.53 B110580.73±17.96 bB123.2±3.21 cC
B220589.8±11.53 bAB132.49±12.69 bcABC
B330608.67±10.03 abAB145.35±2.46 aAB
B440654.37±15.64 aA147.11±11.17 aA
B550600.5±8.36 bAB138.24±5.81 abABC
B660582.37±16.01 bB129.02±8.22 bcBC
B110282.1±127.25 dD61.98±23.51 eE
B220359.13±11.74 cC78.31±3.56 dDE
B330362±17.52 cC81.16±3.70 dD
B440367.8±15.98 cC87.6±4.36 dD
B550358.43±20.35 cC83.07±5.66 dD
B660353.27±17.70 cC82.55±3.72 dD
B110180.5±27.82 eE40.55±8.43 fF
B220181.8±26.23 eE39.23±7.29 fF
B330182.9±15.49 eE41.79±4.57 fF
B440185±9.04 eE41.51±2.42 fF
B550173.4±10.00 eE38.6±2.50 fF
B660172.23±11.04 eE36.87±3.13 fF
B11073.43±28.53 fF14.78±2.77 gG
B22076.43±24.76 fF17.3±5.48 gG
B33082.17±20.30 fF18.93±5.65 gG
B44087.23±15.47 fF21.08±6.25 gG
B55082.37±17.53 fF19.44±5.63 gG
B66076.73±19.30 fF17.95±5.13 gG
Fig. 3 Effects of different treatment combinations on plant productivity of forage sweet sorghum
Conclusions and Discussion
Effects of different planting densities on plant productivity of feeding sweet sorghum planted in autumn vacant field
Planting density significantly affected the plant productivity of forage sweet sorghum planted in autumn vacant field. With the planting density of Nengsi1 increasing from 75 000/hm2 to 525 300 plants/hm2， the fresh weight per plant decreased from 602.74 g/plant to 79.73 g/plant， and the dry weight per plant decreased from135.90 g/plant to 18.25 g/plant， indicating that the plant productivity of forage sweet sorghum had a decreasing trend with the planting density increasing[7，9]. Among the various treatments， the planting density of 75 000/hm2 gave the highest productivity. Under the planting density of 75 000/hm2， its fresh weight per plant （602.74 g/plant） increased by 42.41%-86.77% compared with other planting densities， and its dry weight per plant （135.90 g/plant） increased by 41.79%-86.58% compared with other planting density. This is because that the plants of forage sweet sorghum are high， and excessive close planting is not proper. If the planting density is too high， the population competitiveness is improved， the individual competitiveness is reduced[14-16]， thus inhibiting the yield increasing potential of single plant， so the biological yield per unit area is low. If the planting density is too small， environment resources including light， heat， water and fertilizer could not be utilized sufficiently，which would finally affect the biological yield of the plant. Rational close planting could adjust population structure and the competitiveness between individuals in the population. It is not only a basic condition for normal growth per plant of feeding sweet sorghum， but also an effective measure for coordinating the growth of individual sweet sorghum plant and the growth of population， and should be paid with high attention in production. Effects of different row placing on plant productivity of feeding sweet sorghum planted in autumn vacant field
Row spacing significantly affected the plant productivity of forage sweet sorghum planted in autumn vacant field. With the row spacing increasing from 10 to 60 cm， the plant productivity increased with the row spacing increasing， exhibiting a parabolic trend of increasing at first and decreasing then， indicating that a toosmall or toolarge row spacing. A proper row spacing is a key technique of constructing a rational population structure and better giving play to the yield increasing potential of single plant. If the row spacing is too smaller， the population structure is imbalanced， the competition between individuals in the population would be intensified， and it is impossible to give play to the yield increasing potential of single plant， which discords with the research result of Xu et al.[15]. If the row spacing is too large， the conditions of shortened plant spacing， overlapped leaves， insufficient sunlight， reduced heat， improved intraspecific competiveness and reduced individual competitiveness are caused， resulting in reduced yield， which agrees with the research result of Dai et al.[17]. Under the experimental condition， the row spacing of 40 cm gave the highest plant productivity. Under the row spacing， the fresh weight per plant （323.60 g/plant） increased by 4.53%-13.72% compared with other row spacing， and the dry weight per plant （74.32 g/plant） increased by 3.38%-19.09% compared with other row spacing. The plant productivity was the lowest under the row spacing of 10 cm. Under the row spacing， the fresh weight and dry weigh per plant were， respectively，279.19 and 60.13 g/plant， which were remarkably lower than those under other row spacing. The results showed that the row spacing of 30-50 cm is suitable， and 40 cm is the most suitable row spacing. The suitable row spacing not only could adjust population structure and the competitiveness between individuals in the population， but also could regulate the growth of individual sweet sorghum plant and the growth of population， thereby giving play to the yield increasing potential of single plant.
Effect of treatment combinations on plant productivity of feeding sweet sorghum planted in autumn vacant field
The treatment combinations in this study significantly affected the plant productivity of forage sweet sorghum planted in autumn idle field. Among the 24 treatment combinations， treatment A1B4 showed the highestplant productivity.For treatment A1B4， the fresh weight per plant （654.37 g/plant） was not significantly different from that of A1B3， and the dry weight per plant （147.11 g/plant） was not significantly different from those of treatments A1B3 and A1B5， but the two values were significantly different from those of other treatments. Treatments A1B3 and A1B5 exhibited higher plant productivity. The two treatments showed the fresh weights per plant over 600.00 g/plant， and the dry weights per plant over 138.00 g/plant. The fresh weights and dry weights were not significantly different from those of treatments A1B2 and A1B6， but very significantly different from those of other treatments. Treatment A4B1 exhibited the lowest plant productivity. The results indicate that treatment A1B4 is the optimal combination capable of giving play to the yield increasing potential of Nengsi 1. Determining A1B4 of planting density and row spacing as the optimal combination producing the highest plant productivity
Dai et al.[17] reported the effects of different densities and row spacing on the yield of maize. They deems that the planting density and row spacing both have significantly effects on yield， and the interaction between plant density and row spacing has no significant effect， which accords with the result in this study. Under the experiment conditions， as the planting density did not react with row spacing， the effects of the optimal main treatment A1 and the optima subtreatment B4 could be added， forming the optimal combination （A1B4） producing the highest productivity of single plant， i.e.， the planting density of 75 000/hm2plus the row spacing of 40 cm， which accorded with the optimal treatment combination which could give play to the yield increasing potential of Nengsi 1. Whether the optimal combination is the optimal combination of fodder yield still needs further study.
References
[1] SONG CH， SUN XB， LYU SQ， et al. High efficiency cultivation system for sugarbeet variety Gantang 6[J].SugarCropsofChina，2015，37（4）：49-50.
[2] LIANG X， LI GY， WEI SJ，et al. The introduction experiment for feed sugar broom corn grass in Guangxi[J]. Journal of Anhui Agricultural Sciences，2010，38（35）：20136-20138.
Key words Autumnidle land； Forage sweet sorghum； Planting density； Row spacing； Plant productivity
Received： August 19， 2017 Accepted： October 29， 2017
Supported bySpecial Fund for Agroscientific Researchin the Public Interest （20120304201）.
Hanzhang ZHOU（1960-）， male， P. R. China， researcher， devoted to research about plant protection and cultivation technology of annual fodder crops， Email： [email protected].
*Corresponding author. Email： [email protected]； Email： [email protected]
Sweet sorghum[Sorghum bicolor （L.）Moench] is a crop in Sorghum of Gramineae family， which serves as a forage， sugar and energy crop. Sweet sorghum as an important common forage crop， has the characteristics of high drought resistance， strong tolerance to waterlogging， lower fertility and salinealkaline soil， and strong reproducing property[1-2]. The plant is high with lush stems and leaves， rich in sugar， and has good palatability. It could be fed after ensiling， or prepared into grass meal or other grass products[3-4]， mainly silage. Planting forage sweet sorghum in autumn idle field could take full advantage of natural resources including light， air， heat， water， soil and fertilizer and improve the cropping index of land， and is thus of great significance to the improvement of farmers income and the promotion of rapid， sustainable and stable development of feeding sweet sorghum industry and animal husbandry.
The plant productivity of forage sweet sorghum is composed of the weights of the stem， leaves and ear， as well as an important factor affecting the biological yield of sorghum. Planting density and row spacing are effective measures for the regulation of the contradictory between plant growth and population growth. The research on the relationship between each of planting density and row spacing and plant productivity is of great significance to the investigation of the variety of forage sweet sorghum planted in autumn idle field and its high yield technique. There are many studies on plant productivity. Sheng et al.[5]studied the plant density of sparselyplanted seedlings raised on fertilized dryland bed in rice. Xu et al.[6] clearly defined the technique of plant productivity of millet. Yan et al.[7]investigated the relationship between plant productivity and density of wheat. Guo et al.[8] performed correlation analysis between main agronomic traits and plant productivity with a new peanut variety as study object. Yang et al.[9]deemed that the increase of planting density would reduce the plant productivity of wheat. Currently， there were no studies on the plant productivity of forage sweet sorghum cultivated in autumn idle field. In this study， with Sorghum bicolor cv. Nengsi No.1 as a tested crop， the optimal combination of planting density and row spacing and corresponding effect on plant productivity of forage sweet sorghum were investigated， so as to provide data basis and technical support for the highyield highefficiency cultivation technique of forage sweet sorghum in autumn idle field. Materials and Methods
Experimental materials
The tested cultivar was Sorghum bicolorcv. Nengsi No.1 （provided byInstitute of Millet Crops，Hebei Academy of Agriculture and Forestry Sciences/Hebei Branch Center of National Sorghum Improvement Center）.
General situation of experiment field
The experiment was carried out in Dongke Village， Luancheng District， Shijiazhuang City. The village is located at 37°58′32″ northern latitude，114°36′33″ east longitude， with an altitude of 56 m. The experimental field is flat with convenient drainage and irrigation. The soil has a proper soil moisture content with medium fertility. The soil is loam， with a soil organic matter of 1.73%， a total nitrogen content of 1.12 g/kg， a alkalihydrolyzale nitrogen content of 79.5 mg/kg， a rapidly available phosphorus content of 22.3 mg/kg and a rapidly available potassium content of 113.9 mg/kg， and the soil has a pH value of 7.2.
Experimental methods
Experimental design
Twofactor split plot experimental design was adopted[10-11]. The main plot treatments were about the density of reserved seedlings， which was designed with four levels， i.e.， 75 000， 225 000， 375 000 and 525 300 plants/hm2， which were represented by A1， A2， A3 and A4， respectively. The subplot treatments were about row placing， which was designed with six levels， i.e.， 10， 20， 30， 40， 50 and 60 cm， which were represented by B1， B2， B3， B4， B5 and B6， respectively. The main plots and subplots were all in random arrangement， with three replicates， and there were 72 plots in total. Each subplot had an area of 20 m2 （4 m×5 m）， and an observation way with a width of 1.0 m was reserved between two subplots. A protection region with a width of 1 m was reserved around the experimental field.
The previous crop was oil sunflower， which was harvested on July 26. July 28 was cloudy with showers， July 29 encountered moderate rain， and shower happened fromJuly 30 in the night of to July 31 in the night. Ploughing was performed on August 3-4， and seeding was performed on August 7.Artificial sowing in drill was adopted with a seeding depth of 3-4 cm， and the sown seeds were covered uniformly and then stepped on. Thinning was performed during the period of 2-3 leaves， and the final singling was performed during the period of 4-6 leaves. No base fertilizer was applied before seeding， and topdressing was not performed after seeding.
Determination items and methods The rice was cut on October 28. Three rows were selected from each plot， and 10 plants were continuously cut and mixed uniformly. Then， 10 plants were randomly selected from each plot and labeled （to give clear indication of species， treatment number， and cutting and sampling time）.The plants were weighed and airdried to a water content of 13%-15%， and the dry weight was then measured， so as to calculate the productivity of single plant. The productivity of single plant was represented by fresh weight or dry weight of single plant.
Data processing and analysis
The experimental data was processed with Microsoft Excel 2010. Statistical analysis and plotting were performed in IBM.SPSS.Statistics.v22. Each block （replicate） was analyzed as one factor. The variance analysis of the main plot and subplot factors should select different error terms， and Eb=MS（R（A）） and Ec=MS（e） were used as the error terms for the test of main plot factor （Ai） and subplot factor （Bj）， respectively. Multiple comparisons were then performed by LSD method[10， 12-13]. All the statistical results were represented by "mean ± SD".
Results and Analysis
Effects of various treatments on the productivity of single sweet sorghum plant
Table 1 showed the fresh weight and dry weight per plant of Nengsi 1 under various treatments. The data showed that with the planting density increasing， the plant productivity decreased linearly； and with the row spacing increasing， the plant productivity exhibited a parabolic trend. Variance analysis （Table 2） showed that for different blocks （replicates）， the fresh weight and dry weight per plant exhibited F values of （Sig. of 0.455（Sig.=0.655， i.e.， P>0.05） and 2.923 （Sig.=0.130>0.05）， respectively，i.e.， there were significant differences， indicating that there were no big differences between blocks （replicates）， and the fertility was uniform， thereby reducing the error caused by nonuniform fertility. For the main plottreatments （planting density）， the fresh weight and dry weight per plant had F values of 1 770.86 and 1 918.028， respectively， and the significant values （Sig.） were all 0.000<0.01， i.e.， the differences between treatments were very significant， indicating that different planting densities greatly affected the plant productivity of Nengsi 1； for the subplot treatments （row placing）， the fresh weight and dry weight per plant showed F values （Sig.） of 2.373 （Sig.=0.056>0.05） and 4.781 （Sig.=0.002<0.01）， respectively， i.e.， there were no significant differences in the fresh weight per plant， but the dry weight per plant differed significantly， indicating that row spacing had certain effect on the plant productivity of Nengsi 1. As to the planting density and row spacing interaction， the fresh weight and dry weight per plant showed the F values （Sig.） of 0.491（Sig.= 0.811>0.05） and 1.259 （Sig.=0.272>0.05）， i.e.， there were no significant differences， indicating that the planting density did not interact with row spacing， i.e.， the effect of planting density did not change with the change of row spacing， and the effect of row planting also did not change with the change of planting density. Effect of different planting densities on the productivity of single sweet sorghum plant
It could be seen from Table 3 that with the planting density of Nengsi 1 increasing from 75 000/hm2 to 525 300 plants/hm2， the fresh weight per plant decreased from 602.74 to 79.73 g/plant， and the dry weight per plant decreased from 135.90 to 18.25 g/plant. The differences reached the very significant level， indicating that the planting density had a significant effect on the productivity of single plant. Nengsi 1 had the highest productivity under the planting density of 75 000/hm2 （Fig. 1）. Under the planting density of 75 000/hm2， its fresh weight per plant （602.74 g/plant） increased by 42.41%-86.77% compared with other planting densities， and its dry weight per plant （135.90 g/plant） increased by 41.79%-86.58% compared with other planting density， exhibiting very significant differences. The planting density， 225 000 plants/hm2 produced a middle productivity. Under the planting density of 225 000 plants/hm2， the fresh weight and dry weight per plant were 347.12 and 79.11 g/plant， respectively. The fresh weight per plant decreased by 73.64% compared with the planting density of 75 000/hm2， but increased by 48.35% and 77.03% compared with the planting densities of 375 000 and 525 300 plants/hm2， respectively， with very significant differences. The dry weight per plant decreased by 71.79% compared with the planting density of 75 000/hm2，but increased by 49.74% and 76.94% compared with the planting densities of 375 000 and 525 300 plants/hm2， respectively， with very significant differences.Under the planting density of 525 300 plants/hm2， the productivity was the lowest. Specificity， the fresh weight and dry weight per plant were 79.73 and 18.25 g/plant， respectively， and compared with fresh weight and dry weights under other planting densities， the value decreased remarkably， with very significant differences. The results showed that with the planting density increasing， the population competitiveness of Nengsi 1 increased， which inhibited the yield increasing potential of single sweet sorghum plant， resulting in reduced plant productivity.
Table 1 Results of plant productivityunder different planting density and row spacing treatments
Density∥104plants/hm2Row spacing ∥cm
Fresh weight∥g/plant
IIIIIIMean
Dry weight∥g/plant
IIIIIIMean
A17.5
A222.5
A337.5
A452.5
B110560.60586.50595.10580.73124.01125.93119.67123.20 B220596.90576.50596.00589.80117.87140.60139.00132.49
B330599.90606.50619.60608.67146.53142.53147.00145.35
B440666.80659.50636.80654.37152.00155.00134.33147.11
B550591.60601.70608.20600.50144.93135.40134.40138.24
B660595.10564.40587.60582.37122.00127.00138.07129.02
Mean601.82599.18607.22602.74134.56137.74135.41135.90
B110365.10345.60135.60282.1071.2079.4935.2661.98
B220368.60346.00362.80359.1379.2481.3174.3878.31
B330342.10368.80375.10362.0076.9884.0082.5181.16
B440351.00369.60382.80367.8087.7683.1691.8787.60
B550338.10358.40378.80358.4377.7682.4289.0283.07
B660334.00357.00368.80353.2786.8580.3380.4782.55
Mean 349.82357.57333.98347.1279.9781.7975.5979.11
B110207.10151.60182.80180.5048.6731.8441.1340.55
B220211.10160.50173.80181.8047.4933.7136.4939.23
B330200.00169.80178.90182.9047.0039.9138.4741.79
B440186.00175.50193.50185.0039.0543.8841.6041.51
B550166.10169.30184.80173.4037.3741.4836.9638.60
B660161.80171.10183.80172.2336.4040.2134.0036.87
Mean188.68166.30182.93179.3142.6638.5138.1139.76
B11051.2063.50105.6073.4312.2914.2917.7614.78
B22063.1061.20105.0076.4314.2014.0823.6317.30
B330102.5082.1061.9082.1724.6018.8913.3018.93
B440103.1086.4072.2087.2327.8419.8815.5221.08
B55086.3097.6063.2082.3722.4422.9312.9419.44
B66093.2081.5055.5076.7322.0919.5612.2117.95
Mean83.2378.7277.2379.7320.5818.2715.8918.25
Agricultural Biotechnology2018
Table 2 Variance analysis of the effects of different planting densities and row spacing on plant productivity （intersubject simple effect test）
Determined index Source of variation III type of squares dfMean square FSig.
Fresh weight Replicate 483.3872241.6930.4550.655
Density 2 824 894.1103941 631.371 770.860.000
Error 3 190.4216531.737b
Row spacing 12 859.47252 571.8942.3730.056
Density*row spacing 3 190.4216531.7370.4910.811
Error 43 345.446401 083.636c
Dry weight Replicate 146.433273.2162.9230.130
Density 144 126.820348 042.2731 918.0280.000
Error 150.286625.048b
Row spacing 1 473.3935294.6794.7810.002
Density* row spacing 1 163.6821577.5791.2590.272
Error 2 465.3174061.633c
b. MS（replicate （density））， c. MS（error）.
Table 3 Productivity of single sweet sorghum plant under different plant density and its comparison results TermsDensity of reservedseedlings104 plants/hm2Weight of singleplant∥g
7.50∥104 plants/hm2
（increase/decrease）（±%）
22.50∥104 plants/hm2
（increase/decrease）（±%）
37.50∥104 plants/hm2
（increase/decrease）（±%）
52.53∥104 plants/hm2
（increase/decrease）（±%）
Fresh weight7.50602.74±28.25 aA-255.62*-73.64-423.43*-236.15-523.01*-655.98
22.50347.12±54.66 bB255.62*42.41-167.82*-93.59-267.39*-335.36
37.50179.31±16.13 cC423.43*70.25167.82*48.35-99.58*-124.89
52.5379.73±18.63 dD523.01*86.77267.39*77.0399.58*55.53
Dry weight7.50135.9±11.19 aA-56.79 *-71.79-96.15*-241.81-117.66*-644.69
22.5079.11±12.08 bB56.79 *41.79-39.35*-98.98-60.86*-333.50
37.5039.76±4.77 cC96.15*70.7539.35*49.74-21.52*-117.87
52.5318.25±4.86 dD117.66*86.5860.86*76.9421.51*54.1
（1） In the same column， different lowercase and uppercase letters indicate differences significant at 0.05 and 0.01 levels， respectively. （2） *indicates the significant level of the differences of means at 0.05. Similarly hereinafter.
Fig. 1 Effects of different planting densities on plant productivity of forage sweet sorghum
Effects of different row placing on the productivity of single sweet sorghum plant
It could be seen from Table 4 that the row spacing had an important effect on the productivity of single sweet sorghum plant. The row placing of 40 cm gave the highest productivity of single plant. The fresh weight per plant （323.60 g/plant） increased by 4.53%-13.72% compared with other row spacing， with nonsignificant differences from those under the row spacing of 20， 30 and 50 cm， but significant differences from those under the row spacing of 10 and 60 cm. The dry weight per plant （74.32 g/plant） increased by 3.38%-19.09% compared with other row spacing， with nonsignificant differences from those under the row spacing of 30 and 50 cm， but significant differences from those under the row spacing of 20 and 60 cm and a very significant difference from that under the row spacing of 10 cm. The row spacing of 30 cm gave the highest productivity of single plant. Specifically， the fresh weight per plant （308.93 g/plant） was not significantly different from those under the row spacing of 20 and 50 cm， but significantly different from those under the row spacing of 10 and 60 cm； and the dry weight per plant （71.81 g/plant） had a very significantly difference from that under the row spacing of 10 cm， but was not significantly different from those under other row spacing. The plant productivity was the lowest under the row spacing of 10 cm. Under the row spacing， the fresh weight and dry weigh per plant were， respectively，279.19 and 60.13 g/plant， which were remarkably lower than those under other row spacing. Under the experimental conditions， the row spacing of 30-50 cm is suitable， and 40 cm is the most suitable row spacing （Fig. 2）. Fig. 2 Effects of different row spacing on plant productivity of forage sweet sorghum
Table 4 Effects of different row spacing on the productivity of single sweet sorghum plant
Row spacingcm
Fresh weight
g/plant%
Dry weight
g/plant%
10279.19±59.37 bB13.7260.13±12.48 cB19.09
20301.79±58.87 abAB6.74 66.83±13.34 bAB10.08
30308.93±60.43 aAB4.53 71.81±14.49 abA3.38
40323.60±65.19 aA-74.32±14.70 aA-
50303.68±59.86 abAB6.16 69.84±13.85 abA6.03
60296.15±58.27 bAB8.48 66.60±13.04 bcAB10.39
Effects of different treatment combinations on the productivity of single sweet sorghum plant
It could be seen from Table 5 that the productivity of Nengsi 1 differed among the 24 treatments. Among the various treatments， treatment A1B4 showed the highest plant productivity， and the fresh weight per plant （654.37 g/plant） was not significantly different from that of A1B3， but significantly different from those of other treatments； and the dry weight per plant （147.11 g/plant） was not significantly different from those of treatments A1B3 and A1B5， but significantly from that of treatment A1B2 and very signifi cantly different from those of other treatments. Treatments A1B3 and A1B5 exhibited higher plant productivity. The two treatments showed the fresh weights per plant over 600.00 g/plant， and the dry weights per plant over 138.00 g/plant. The fresh weights and dry weights were not significantly different those of treatments A1B2 and A1B6， but very significantly different from those of other treatments. Treatment A4B1 exhibited the lowest plant productivity. Its fresh weight and dry weigh per plant were 73.43 and 14.78 g/plant， respectively. This treatment was not significantly different from treatments A4B2， A4B3， A4B4， A4B5 and A4B6 in both the fresh weight and dry weight per plant. The results showed that the treatment combinations have important effects on the productivity of single sweet sorghum plant， and treatments A1B3， A1B4 and A1B5 are optimized combination capable of giving play to the yield increasing potential of Nengsi 1， while treatment A1B4 is the optimal combination （Fig. 3）.
Table 5 Effects of different treatments on the productivity of single sweet sorghum plant
Treatment combination
Density∥104 plants/hm2Row spacing∥cmFresh weight∥g/plantDry weight∥g/plant
A17.50
A222.50
A337.50
A452.53 B110580.73±17.96 bB123.2±3.21 cC
B220589.8±11.53 bAB132.49±12.69 bcABC
B330608.67±10.03 abAB145.35±2.46 aAB
B440654.37±15.64 aA147.11±11.17 aA
B550600.5±8.36 bAB138.24±5.81 abABC
B660582.37±16.01 bB129.02±8.22 bcBC
B110282.1±127.25 dD61.98±23.51 eE
B220359.13±11.74 cC78.31±3.56 dDE
B330362±17.52 cC81.16±3.70 dD
B440367.8±15.98 cC87.6±4.36 dD
B550358.43±20.35 cC83.07±5.66 dD
B660353.27±17.70 cC82.55±3.72 dD
B110180.5±27.82 eE40.55±8.43 fF
B220181.8±26.23 eE39.23±7.29 fF
B330182.9±15.49 eE41.79±4.57 fF
B440185±9.04 eE41.51±2.42 fF
B550173.4±10.00 eE38.6±2.50 fF
B660172.23±11.04 eE36.87±3.13 fF
B11073.43±28.53 fF14.78±2.77 gG
B22076.43±24.76 fF17.3±5.48 gG
B33082.17±20.30 fF18.93±5.65 gG
B44087.23±15.47 fF21.08±6.25 gG
B55082.37±17.53 fF19.44±5.63 gG
B66076.73±19.30 fF17.95±5.13 gG
Fig. 3 Effects of different treatment combinations on plant productivity of forage sweet sorghum
Conclusions and Discussion
Effects of different planting densities on plant productivity of feeding sweet sorghum planted in autumn vacant field
Planting density significantly affected the plant productivity of forage sweet sorghum planted in autumn vacant field. With the planting density of Nengsi1 increasing from 75 000/hm2 to 525 300 plants/hm2， the fresh weight per plant decreased from 602.74 g/plant to 79.73 g/plant， and the dry weight per plant decreased from135.90 g/plant to 18.25 g/plant， indicating that the plant productivity of forage sweet sorghum had a decreasing trend with the planting density increasing[7，9]. Among the various treatments， the planting density of 75 000/hm2 gave the highest productivity. Under the planting density of 75 000/hm2， its fresh weight per plant （602.74 g/plant） increased by 42.41%-86.77% compared with other planting densities， and its dry weight per plant （135.90 g/plant） increased by 41.79%-86.58% compared with other planting density. This is because that the plants of forage sweet sorghum are high， and excessive close planting is not proper. If the planting density is too high， the population competitiveness is improved， the individual competitiveness is reduced[14-16]， thus inhibiting the yield increasing potential of single plant， so the biological yield per unit area is low. If the planting density is too small， environment resources including light， heat， water and fertilizer could not be utilized sufficiently，which would finally affect the biological yield of the plant. Rational close planting could adjust population structure and the competitiveness between individuals in the population. It is not only a basic condition for normal growth per plant of feeding sweet sorghum， but also an effective measure for coordinating the growth of individual sweet sorghum plant and the growth of population， and should be paid with high attention in production. Effects of different row placing on plant productivity of feeding sweet sorghum planted in autumn vacant field
Row spacing significantly affected the plant productivity of forage sweet sorghum planted in autumn vacant field. With the row spacing increasing from 10 to 60 cm， the plant productivity increased with the row spacing increasing， exhibiting a parabolic trend of increasing at first and decreasing then， indicating that a toosmall or toolarge row spacing. A proper row spacing is a key technique of constructing a rational population structure and better giving play to the yield increasing potential of single plant. If the row spacing is too smaller， the population structure is imbalanced， the competition between individuals in the population would be intensified， and it is impossible to give play to the yield increasing potential of single plant， which discords with the research result of Xu et al.[15]. If the row spacing is too large， the conditions of shortened plant spacing， overlapped leaves， insufficient sunlight， reduced heat， improved intraspecific competiveness and reduced individual competitiveness are caused， resulting in reduced yield， which agrees with the research result of Dai et al.[17]. Under the experimental condition， the row spacing of 40 cm gave the highest plant productivity. Under the row spacing， the fresh weight per plant （323.60 g/plant） increased by 4.53%-13.72% compared with other row spacing， and the dry weight per plant （74.32 g/plant） increased by 3.38%-19.09% compared with other row spacing. The plant productivity was the lowest under the row spacing of 10 cm. Under the row spacing， the fresh weight and dry weigh per plant were， respectively，279.19 and 60.13 g/plant， which were remarkably lower than those under other row spacing. The results showed that the row spacing of 30-50 cm is suitable， and 40 cm is the most suitable row spacing. The suitable row spacing not only could adjust population structure and the competitiveness between individuals in the population， but also could regulate the growth of individual sweet sorghum plant and the growth of population， thereby giving play to the yield increasing potential of single plant.
Effect of treatment combinations on plant productivity of feeding sweet sorghum planted in autumn vacant field
The treatment combinations in this study significantly affected the plant productivity of forage sweet sorghum planted in autumn idle field. Among the 24 treatment combinations， treatment A1B4 showed the highestplant productivity.For treatment A1B4， the fresh weight per plant （654.37 g/plant） was not significantly different from that of A1B3， and the dry weight per plant （147.11 g/plant） was not significantly different from those of treatments A1B3 and A1B5， but the two values were significantly different from those of other treatments. Treatments A1B3 and A1B5 exhibited higher plant productivity. The two treatments showed the fresh weights per plant over 600.00 g/plant， and the dry weights per plant over 138.00 g/plant. The fresh weights and dry weights were not significantly different from those of treatments A1B2 and A1B6， but very significantly different from those of other treatments. Treatment A4B1 exhibited the lowest plant productivity. The results indicate that treatment A1B4 is the optimal combination capable of giving play to the yield increasing potential of Nengsi 1. Determining A1B4 of planting density and row spacing as the optimal combination producing the highest plant productivity
Dai et al.[17] reported the effects of different densities and row spacing on the yield of maize. They deems that the planting density and row spacing both have significantly effects on yield， and the interaction between plant density and row spacing has no significant effect， which accords with the result in this study. Under the experiment conditions， as the planting density did not react with row spacing， the effects of the optimal main treatment A1 and the optima subtreatment B4 could be added， forming the optimal combination （A1B4） producing the highest productivity of single plant， i.e.， the planting density of 75 000/hm2plus the row spacing of 40 cm， which accorded with the optimal treatment combination which could give play to the yield increasing potential of Nengsi 1. Whether the optimal combination is the optimal combination of fodder yield still needs further study.
References
[1] SONG CH， SUN XB， LYU SQ， et al. High efficiency cultivation system for sugarbeet variety Gantang 6[J].SugarCropsofChina，2015，37（4）：49-50.
[2] LIANG X， LI GY， WEI SJ，et al. The introduction experiment for feed sugar broom corn grass in Guangxi[J]. Journal of Anhui Agricultural Sciences，2010，38（35）：20136-20138.