ABSTRACT

The study results of the time and quantity of hybrid rapeseed base-stem position branching and the contribution of each branch to the whole plant yield show that, under the ultra-low density planting condition from 60,000 plants per hectare to 7,500 plants per hectare and with a reduction of density, the base-stem position branching, the number of plant pod and pod grain, and the proportion of yield of base-stem position branching in whole plant get increased. The main factors that affect the branching potential and effectiveness of base-stem position branching are sowing time and density. Under ultra-low density planting condition and with more branches, the proportion of high position branching in yield will decrease, but the proportion of base-stem position branching in yield will increase. The yield will reach a high level owing to plenty of base-stem position branching, secondary branching and pods of plant.

The high yield cultivation technology in hybrid rapeseed under ultra-low density planting requies that individual plant should get well developed in population. The structure and yield of individual plant rely on branches. So it is very useful to learn the branching potential under ultra-low density planting for knowing the importance and utilization of the base-stem position branching.

MATERIALS AND METHODS

Time, Location and Soil Condition of Trial

The trials were carried out at double-season-late–rice region of Yitai, Wuhu County, Anhui Province of China from 1993 to 1998. The soil condition: pH 5.8, organic materials 27.6 g/kg, total N 1.54 g/kg, total P 0.28 g/kg, total K 13.1 g/kg, avail P 5 mg/kg, avail k 68 mg/kg, ECE 19.30 me/100g soil, bulk density 1.17 g/cm³ and porosity 55.34.The soil is of sticky clay rice soil. The trial variety is Qinyou No. 2.

Density Trial

During 1996-1997, in a 25m² plot, the densities were tested with five treatments, namely density of 3,750 plants, 7,500 plants, 15,000 plants, 30,000 plants and 60,000 plants per hectare. Nursering seedlings was made on August 20 and transplanting on October 14, three replications, on random.

Sowing Date Trial

In 1995-1996, in a 36m² plot, five sowing times were given, namely August 10, 20, 30 and September 9, 19. Density was 15,000 plants/ha, and they were transplanted on October 16, no replication, in order of range. In addition, through comparison trial between early sowing (early transplanting) and late sowing (late transplanting), an observation of relation between leaf and branch in over-winter in years was done.

Trial of Interaction between Sowing Date and Density

In 1993-1995, trials were made with the same five sowing times and density as above in a 36 m² plot, and all transplantings were done on October 16, no replication, in order of range. The observation of the trail was for law of leaf and branch development.

Yield Comparison between Branch and Plant

In 1996-1998, 20 plants with 30 and 15 first branches were elected separately from trail fields of high yield cultivation with their densities being 7,500 plants and 60,000 plants per hectare. Among them, 10 evenly grown plants were elected for investigating agronomic character and yield of plants in order to learn distribution of branching to yield.

RESULTS

Effect of Branches on Factor of Yield Composition

There are great differences in composition of yield factors on branching number, pod number, pod grain number, grain weight of base-stem position and bolt-stem position (Table 1) under the ultra-low density planting condition.

Base-stem position branching of 3,750-plant per hectare has tertiary branches besides primary and secondary branches. On the average, 286.5 branches per plant and 7,057.5 pods per plant. To whole plant, base-stem position branching makes up to 60.42% of all branches, with their pod number being 61.18% of all pods and their grain weight 59.72% of all grain weight. The ratio of yield between base-stem position branching and bolt-stem position branching is 3:2. Yield per plant and per hectare is 496.58 g and 1,862.18 kg, respectively.

In the plot that its density is 7,500 plants per hectare, the average branches of per plant are 294.6, and base-stem position branching number of per plant makes up 59.44% of all branches, with their pod number being 60.22% of all pods and their grain weight 59.26% of all grain weight. The ratio of yield between base-stem position branching and bolt-stem position branching is 3:2. Yield per plant is 502.84 g, namely the yield per hectare is 3,771.3 kg. From the total branching number, pod number, grain weight of per plant to the density of 3,750 plants per hectare and 7,500 plants per hectare, they both are almost the same, but their yields differ one time. So it is easy to learn the reason that yield decrease from the ultra-low density with 3,750 plants per hectare.

In the plot with a density of 15,000 plants per hectare, the branches of per plant are 155.5, 47.2% less than the density in 7,500 plants per hectare. Among them, base-stem position branching makes up 57.2%.

The plots cultivated with 30,000 and 60,000 plants generally have no tertiary branches, and primary and secondary branches are reduced greatly. Pod number and grain weight of per plant decrease in inverse proportion to density. Ratios of grain weight of base-stem position and bolt-stem position are 2:3 and 1:7.5, respectively. Though the yield of per plant decreases, yield per hectare reaches to 3,771.9 kg and 3,697.8 kg and the effects on which the base-stem position branching exerts.

Table 1. Relation between the Density and Constitution of Branching Yield of the Hybrid Rapeseed under Ultra-low Density planting

Density Branching No.of Branching No.of Pods No.of Grains Grain weight

(Plant per hectare) Type Per Plant Per Plant Per Pod

(Branch) (Grain) per plant (g)

Base-stem P B 14.3 1269.7(17.99) 22.5 97.42 (19.62)

position S B 104.1 2544.7(36.06) 20.6 177.18(35.68)

T B 54.7 503.3(7.13) 13.3 21.96(4.42)

3750

Bolt-stem P B 16.9 1309.5(18.55) 22.7 101.66(20.47)

position S B 82.4 1304.4(18.48) 21.2 94.02(18.93)

TB 14.1 125.9(1.78) 10.7 4.34(0.87)

Total or Mean 286.5 7057.5(100.00) 20.75 496.58(100.00)

Base-stem P B 13.7 1206.4(17.01) 22.4 92.15(18.33)

position SB 110.3 2579.9(36.37) 21.1 185.08(36.81)

TB 51.1 485.3(6.84) 13.1 20.73(4.12)

7500

Bolt-stem P B 17.7 1342.5(18.93) 22.5 103.00(20.48)

position S B 87.9 1361.4(19.19) 21.2 98.13(19.52)

TB 13.9 117.5(1.66) 9.9 3.75(0.75)

Total or Mean 294.6 7093.0(100.00) 20.87 502.84(100.00)

Base-stem P B 12.4 881.4(23.50) 21.7 65.03(24.66)

position SB 56.9 1102.8(29.40) 20.3 75.22(28.53)

TB 19.8 49.7(1.33) 9.4 1.46(0.55)

15000

Bolt-stem P B 13.5 909.6(24.25) 21.8 67.62(25.64)

position S B 41.6 781.1(20.82) 20.4 53.70(20.37)

TB 11.3 26.3(0.70) 8.2 0.65(0.25)

Total or Mean 155.5 3750.9(100.00) 20.78 263.68(100.00)

Base-stem P B 4.9 374.3(20.02) 20.7 26.27(20.89)

position S B 29.0 387.1(20.70) 18.4 23.36(18.59)

TB 2.7 15.6(0.83) 7.9 0.36(0.29)

30000

Bolt-stem PB 14.9 781.4(41.79) 21.4 57.02(45.35)

position S B 27.6 311.3(16.65) 18.5 18.72(14.89)

Total or Mean 79.1 1869.7(100.00) 20.04 125.73(100.00)

Base-stem P B 2.4 79.7(8.28) 18.6 4.77(7.44)

position SB 13.2 48.3(5.02) 16.2 2.49(4.04)

60000

Bolt-stem PB 13.4 617.6(64.16) 20.5 42.67(69.24)

position S B 28.8 217.1(22.55) 16.9 11.70(18.98)

Total or Mean 57.8 962.7(100.00) 19.32 61.63(100.00)

The parenthesis is percent; Primary branching = PB; secondary branching = SB; tertiary branching = TB

Factors and Branching Potential Affecting Base-stem Position Branching Number

Base-stem position branching is interacted by density and sowing time. The trial shows the effect, that rapeseed sowed on August 20 with 7,500 plants per hectare, August 30 with 15,000 plants per hectare and September 9 with 30,000 plants per hectare, is better. Hybrid rapeseed has stronger branching potential. For convenient quantity description, branching potential may be defined by the number of maximum main stem leaf - (the number of winter main stem leaf + the number of autumn-end branches) (Table 2).

Table 2. Relation of Sowing Date and Primary Branching Potential of Hybrid Rapeseed under Ultra-low Density Planting Condition

Sowing-date Autumn(Dec.21) Winter(Feb.10) Spring(Mar.18) Leaf position Potentiality of

On Primary Primary Branches

(month /day) Branching (Branch/plant)

Main Stem Primary Branching Main Stem No.of max main

Leaves on Autumn End Leaves Stem Leaves

(leaf) (Branch/Plant) (leaf) (Leaf)

8/10 35.76 20.6 42.58 58.42 15.16 36.44

8/20 35.84 20.7 42.96 58.84 15.14 36.58

8/30 30.88 15.6 38.02 53.48 15.28 31.06

9/9 25.26 9.9 32.08 46.22 15.46 24.04

9/19 19.18 3.5 25.92 38.66 15.68 16.24

Branching potential = the number of maximum main stem leaf ― (the number of winter main stem leaf + the number of autumn-end branches); Density: 7,500 plants per hectare.

The Effect of Branching Number of Hybrid Rapeseed on the Yield of Single Plant

Pod number, pod grain and branch grain weight of primary branches of 7,500 plants per hectare with 30 branches and 15,000 plants per hectare with 15 branches are examined, and the result shows that pod number with many branches is bigger than that of fewer ones to branches of the same position. The same trend happens to pod grains of branch and grain weight, and upper and low branches are more than middle branches, showing a distribution like V shape, and secondary branches are the same generally. At the same time the study shows also that 7,500 plants per hectare have certain tertiary branches, however 15,000 plants per hectare have no tertiary branches. The density affects branching type and number directly.

DISCUSSION

The branching potential of hybrid rapeseed is great, especially the high yield cultivation of Qinyou No.2 under ultra-low density planting condition with 7,500-60,000 plants per hectare. Its heterosis may be given full play and the average yield per hectare is stable at the level of 3,750 kg per hectare or so.

The cultivation method under the ultra-low density planting condition may obtain higher productivity effects of population by adjusting individual plant productivity of hybrid rapeseed. The method provides an advantageous condition to fully use soil resource for stereoscopical grow of symbiosis of hybrid rapeseed and vegetable. Thus the yield and profits per unit area increase greatly. But it is necessary that early sowing promotes early development, and ensures balanced growth of high yield population, and makes middle and up branches of bolt-stem and big branches of base-stem position get enough nutrient. At the same time, to prevent presenility and to control plant disease and pests are also needed.

Early sowing is a key to the cultivation under ultra-low density planting condition. Generally it is about one month earlier than sowing time of routine density. So seedling transplanting must be prepared in time for bed of seedling.

The above-mentioned cultivation technology of ultra-low density is studied and advanced by us in production practice in recent years. It is a new cultivation technology, and its cultivation physiological and ecological law still needs further studied.

ACKNOWLEDGEMENTS

Thanks to Mr. Dong Huiqing for his translation.