Effects of Row-Spacing on Canopy Structure and Yield in Different Plant Type Rice Cultivars

Zhao Hai-xin , Wang Xiao-xue Guo Zhen-hua, Huang Xiao-qun, and Liu Hua-long

1 Rice Research Institute, Shenyang Agricultural University, Shenyang 100866, China

2 Rice Research Institute, Heilongjiang Academy of Agricultural Sciences, Jiamusi 154026, Heilongjiang, China

3 College of Agriculture, Northeast Agricultural University, Harbin150030, China

Introduction

Improving the growth environment in the field is crucial for the yield formation of crops, in which row spacing plays an important role (Dechard et al.,1978). It has been reported that the wide-narrow row spacing does not have significant advantages over the uniform one in maize (Zea mays L.)(Yang et al.,2010). But these works mainly focus on solving the harvesting problems of corn (Zhang et al., 2010). The optimum row spacing requires for realizing the biggest ear number of wheat (Triticum aestivum L.)varieties is different (Wu et al., 2004). 7.5 t · hm-2grain yields of compact ear type, loose ear type and medium ear type wheat can be obtained through altering the row spacing. The yield of heavy ear wheat can reach about 10 t · hm-2and the dry biomass production of large ear wheat can also be increased by adjusting row spacing(Guo et al., 2006; Yang et al., 2007; Wu et al., 2004).It is for sure that changes of row spacing can improve the yield of crops.

There are different types of rice (Oryza sativa L.)varieties. According to the panicle type or the tillering ability, rice variety can be divided into curved, erect and half erect panicle varieties or strong, middle and weak tillering varieties. The self-adjusting ability of rice population is stronger than that of wheat and maize. Thus, row-spacing strongly affects the growth and yield of rice. Moderately increasing row spacing and reducing planting density accelerate rice yield per hectare (Yan et al., 2007; Chen et al., 2004). As row spacing increase, the number of tillers per plant enhances, but the number of tillers per hectare reduces.The biggest leaf area index (LAI)and its attenuation ratio decrease with the increasing of row-spacing at heading stage (Xia et al., 2006). Wider row-spacing is suitable for curved panicle varieties, which mend the semi-extinction depth and canopy light intensity of the population in the fi eld at fi lling stage (Wang et al.,2005; Tadashi et al., 1996). Whether different types of rice varieties should adopt wider row-spacing to improve the rice yield is still an open question.

Heilongjiang Province in China is one of the highest latitude rice planting areas in the world. The cultivars in this region can be divided into nine types, including more tillers and curved panicle type, middle tillers and curved panicle type, few tillers and curved panicle type, more tillers and erect panicle type, middle tillers and erect panicle type, few tillers and erect panicle type, more tillers and half-erect panicle type, middle tillers and half-erect panicle type and few tillers and half-erect panicle type. The traditional row-holespacing is 30.0 cm×10.0 cm or 30.0 cm×13.2 cm. In this study, the optimum row-spacing for two types of rice varieties, such as more tillers and curved panicle type and few tillers and half-erect panicle type, was characterized. The effects of different row spacings on canopy structure and yield were investigated.

Materials and Methods

Location and natural overview

The experiments were carried out in Rice Research Institute of Heilongjiang Academy of Agricultural Sciences (46°49'N, 130°22'E)in 2008 and 2009. Heilongjiang Province belongs to temperate continental monsoon climate. The annual temperature is about 3℃. The active accumulated temperature (≥10℃)is 2 521℃. The frost-free period is 130-140 days. The annual amount of precipitation is 510 mm. The soil used for the experiments was meadow. pH value of the soil was 6.4. The contents of organic matter, rapidlyavailable phosphorus, rapidly-available potassium,and alkali solution nitrogen value in the soil were 27.0 g · kg-1, 39.78 mg · kg-1, 202.76 mg · kg-1and 126.46 mg · kg-1, respectively.

Materials

Longjing 20 and Longjing 21 (super rice)bred by Rice Research Institute of Heilongjiang Academy of Agricultural Sciences were used as materials.The properties of Longjing 20 or 21 were well characterized. There were 11 or 12 leaves growing in the main stem. The growth period was about 130 or 132 days. The active accumulated temperature required for its maturation was about 2 350℃ or 2 450℃. Longjing 20 belonged to more tillers and curved panicle type (MCP); but Longjing 21 was few tillers and half-erect panicle type (FEP).

Experiment design

In this study, six row-spacing treatment (m1 to m6)were set, which were 33, 30, 27, 24, 21 and 18 cm;hole-spacing for all the row-spacing treatment was the same, 16.7 cm. The experiment adopted randomized block design, and repeated three times. The plot area was 5 m×7 m=35 m2. The nitrogen (N)fertilizer was applied with total amount of 165.6 kg · hm-2(converted into pure N). About 34.5 kg · hm-2(converted into pure N), 69 kg · hm-2(converted into P2O5)and 37.5 kg · hm-2(converted into K2O)were used as basic fertilizer. Other N fertilizer was applied on June 1,June 10 and July 1 with the amount of 34.5 kg · hm-2N each time. Other potassium (K)fertilizer was applied on July 1 with 37.5 kg · hm-2(converted into K2O). The seeds were soaked on April 10. Three to four soaked seeds were sown in each hole of the pots on April 15.The 4-leaf-stage seedlings, then, were transplanted to the fi eld on May 15. Weed control, irrigation and other managements were the same as the conventional fi eld.

Measurement of the morphological, physiological traits and yield

Several morphological and physiological traits and yield were examined in the study.

The highest stem number per square meter (m2)The number of tillers was investigated every two days after June 15. When the number of tillers did not change among three different measurement, three spots from each block, 20 holes from each spot were chosen to observe the max number of tillers per square meter.

Leaf area index (LAI)

A specif i c gravity method was applied to measure the LAI. Three spots of each block and five holes from each spot were chosen for the analysis. The length and max width of the leaves collected from the three medium stems of each hole were measured. Then,the leaves were mixed and put into an oven. After removing the activities of the enzymes at 105℃ for 30 min, the leaves were completely dried at 80℃. The formula for calculating the LAI was as the followings.

LAI=0.78×S×(G′+G0)/G′×S0

Where, S represented the sum of the length multiples the width from the leaves of three medium stems; G' represented the amount of dry matter for the three medium stems; G0represented the amount of the dry matter of the rest leaves of the five holes; S0represented the land area occupied by fi ve holes rice;and 0.78 was coeff i cient.

Percentage of productive tiller

The percentage of productive tiller was calculated by dividing effective panicles per unit area measured after harvesting with max tiller number per unit area.Width of basal internode

Five holes from each block were randomly picked to examine the width of the first stem nodes with micrometer.Yield

After harvesting, fresh grain yield of each block were investigated. Then, the water content of the grains was measured. The economic yields were calculated by taking the water content as 15%.

Other morphological and physiological characters were examined with regular methods after harvesting.

Data analysis

The data collected was calculated by the Excel 2003.The variance and correlation analysis were done by SPSS Statistics. Results from the two years'experiments were consistent with each other. Only the data from experiments in 2009 was shown.

Results

Effect of row-spacing on the highest stem number per square meter

Patterns of the highest stem number per square meter were similar in Longjing 20 and 21. As row-spacing enlarging, the highest stem number per square meter increased fi rst, and then decreased. The stem number per square meter of Longjing 20 was higher than that of Longjing 21 (Fig. 1). The highest stem number per square meter for both of the varieties was observed when the row-spacing was 24 cm in the experiment.But the highest theoretical value of the highest stem number per square meter was found when rowspacing was 22.5 cm for Longjing 20 and 21.4 cm for Longjing 21. The stem number of the two cultivars was the lowest when row-spacing was 33 cm. The stem number of 33 cm row-spacing in the two cultivars was about 16.5% and 22.8% lower than that of 22 cm rowspacing. Relationship between the row-spacing and the stem number of the two cultivars presented quadratic regression (R2=0.7986* for Longjing 20 and R2=0.9005** for Longjing 21). The correlations exhibited significant and extremely significant respectively,suggesting that the row spacing impacted the highest stem number per square meter of the two varieties.

Fig. 1 Relationship between row-spacing and the highest stem number per square meter

The results revealed that the competition in the population restrained the ability of tillering by narrow row-spacing causing the reduction of the stem number per square meter. On the other hand, if the free growing space by wider row-spacing was too large to be occupied by tillering, it would lead to the decrease of the stem number per square meter. The tillering ability of FEP was weaker than that of MCP. The highest stem number per square meter of FEP dropped more dramatically than that of MCP when the row spacing was getting larger. Taking together, our results indicated that 22.5 cm for Longjing 20 and 21.4 cm for Longjing 21 row-spacing were the best row spacing for the stem number per square meter, if the stem number per square meter was the only consideration.

Relationship between row spacing and percentage of productive tiller

As the row spacing increasing, the percentage of productive tiller of both FEP and MCP varieties dropped first then rose (Fig. 2). Row spacing and percentage of productive tiller showed quadratic regression relationship (R2=0.9161** for Longjing 20 and R2=0.7642* for Longjing 21). Correlations was extremely significant and significant, respectively. The percentage of productive tiller in Longjing 20 was the lowest when the row spacing was 21 cm (76.9%)(Fig. 2).As row spacing becoming larger, the percentage of productive tiller increased gradually and reached 87.7% when row spacing was 33 cm, which was 10.8% higher than that of 21 cm row spacing. Effects of row spacing on the percentage of productive tiller in Longjing 21 were similar to that in Longjing 20.However, the percentage of productive tillers of narrow row spacing in Longjing 21 was much higher than that of Longjing 20. The percentage of productive tiller was 85.5% when row spacing was 21 cm. Then,it decreased. The lowest percentage of the productive tiller occurred when row spacing was 24 cm, which was 74.9%, 10.6% lower than that of 21 cm row spacing. Then, it increased gradually. When row spacing was 33 cm, it reached the highest, which was 9.4% higher than that of the lowest one.

Fig. 2 Relationship between row-spacing and percentage of productive tiller

Through the quadratic regression analysis, the percentage of productive tiller could be improved by both narrow and wide row spacing. Because tillering ability of the two types was different, independent variable (row spacing)to the minimum (percentage of productive tiller)of regression equation varied.Theoretical percentage of productive tiller of MCP(Longjing 20)was the lowest when row spacing was 22 cm. If the row spacing was smaller or larger than 22 cm, the percentage of productive tiller of MCP(Longjing 20)increased. However, for FEP (Longjing 21)the percentage of productive tiller increased when row spacing was smaller or larger than 25.7 cm.The row spacing to gain the minimum percentage of productive tiller in MCP was smaller than that of FEP. According to the coefficient of quadratic, the percentage of productive tiller of FEP was much more sensitive to the row spacing than that of MCP.

Effects of row spacing on LAI

As the row spacing increase, the LAI at the later tillering stage of the two varieties increased fi rst and then decreased (Fig. 3). The LAI of Longjing 20 reached the highest (4.06)when row spacing increased to 27 cm. The LAI of Longjing 21 was lower than Longjing 20. The highest LAI of Longjing 21 was only 2.77 when row spacing was 21 cm. The relationship between the row spacing and the LAI of the two varieties followed the quadratic regression (R2=0.6988 for Longjing 20 and R2=0.6248 for Longjing 21)(Fig. 3).

According to the analysis of the repression equation,the LAIs of the two varieties at later tillering stage had extreme values among the range of row spacing treatments. The LAIs of Longjing 20 and Longjing 21 reached the highest when row spacing was 25.7 cm and 19.6 cm, respectively. The LAIs of the two varieties decreased as long as the row spacing was smaller or larger than 25.7 cm for Longjing 20 and 19.6 cm for Longjing 21. The row spacing of the highest LAI in MCP (Longjing 20)was larger than that in FEP (Longjing 21).

Effects of row spacing on dry biomass accumulation

The dry weights of panicle, stem and leaf in Longjing 20 were the highest when row spacing was 30 cm,which were 11438.8, 5878.5 and 1585.1 kg · hm-2,respectively (Table 1). The dry weights of panicle and leaf from the 30 cm row spacing were significantly higher than that from 21 cm and 18 cm row spacing.The dry weights of stem from 30 cm row spacing were significantly higher than that from 33 cm, 27 cm, 21 cm, and 18 cm. As the row spacing getting smaller,ratio of panicle weight to stem weight and ratio of panicle weight to biological yield descended gradually.Whereas, there were no obvious changes in ratio of panicle weight to leaf weight and ratio of stem weight to leaf weight. The dry weights of panicle, stem and leaf in Longjing 21 were becoming heavier as the row spacing getting smaller. The highest dry weights of panicle (10 561.2 kg · hm-2), stem (6 008.2 kg · hm-2)and leaf (1 856.9 kg · hm-2)in Longjing 21 were harvested at 24, 21, and 18 cm row spacing, respectively.The ratio of panicle weight to stem weight, ratio of panicle weight to leaf weight, ratio of stem weight to leaf weight and ratio of panicle weight to biological yield of Longjing 21 increased fi rst and then decreased(Table 1). The best row spacing for dry matter accumulation depended on the types of varieties(Table1). Wider row spacing (30 cm)improved the dry matter accumulation in panicle, stem and leaf of MCP, such as Longjing 20. Conversely, narrower row spacing (24 or 21 cm)was the favorite for dry matter accumulation and yield of FEP, such as Longjing 21.

Table 1 Effects of row-spacing on dry matter accumulation and ratio among panicle, stem and leaf

Effects of row spacing on morphological traits

The effects of row spacing on morphological traits were different between MCP and FEP (Table 2).Row spacing in MCP significantly or extremely significantly, pasitively correlated with the length of the fl ag leaf, the width of the fl ag leaf, the length of the last internode, the length of the last 2nd internode, and the length of panicle (0.89**, 0.85**, 0.85**, 0.96**,and 0.91**), though there was no signif i cant, positive correlation between row spacing and length of the last 3rd internode, length of the last 4th internode and the width of basal stem. Row spacing in FEP had no signif i cantly effects on plant morphological character,though it had positive correlation with the length of the flag leaf, the length of the last 1st internode,length of the last 2nd internode, the width of the basal stem and the length of the panicle and negative correlation with the width of flag leaf, the length of the last 3rd internode and the length of the last 4th internode (Table 2).

Obviously, the morphological characters of MCP were more easily influenced by the row spacing.The influence of row spacing on the morphologies of MCP might affect the yield and the component of yield formation. Thus, row spacing adjustment should help Longjing 20 to elevate its strong tillering characters. The row spacing exerted little effects on the morphological characters of FEP. Therefore,improvement of the space utilization was the theme for FEP to obtain higher yield through row spacing.

Effects of row spacing on yield traits

The correlation coeff i cients between row spacing and primary branch number (PBN, 0.79*), grain number of primary branch (GNPB, 0.82*), or spikelet number of primary branch (SNPB, 0.85*)of MCP were significantly higher than that of the second branch(Table 3). Row spacing positively correlated with the seed setting rate of the primary branch (SSRPB),grain number per panicle (GNP), spikelet number per panicle (SNP)and yield, but negatively correlated with the seed setting rate of the secondary branch (SSRSB,-0.87**)and the seed setting rate per panicle (SSRP).The negative correlation between row spacing and the SSRSB, SSRP or yield (-0.96**)of Longjing 21 was obtained. Row spacing positively correlated with SBN, GNSB or SNSB. The yield of Longjing 20 was the highest (10 012.3 kg · hm-2)when row spacing was 27 cm, which was signif i cantly higher than that of 24,21 and 18 cm row spacing treatments. The yields of Longjing 21 increased as row spacing decrease. When row spacing was 21 cm, the highest yield (10 080.7 kg · hm-2)of Longjing 21 was observed, which was signif i cantly higher than that of 33, 30 and 27 cm row spacing treatments.

Table 2 Correlation index between row-space and morphological traits

Table 3 Correlation index between row-space and yield traits

Row spacing positively correlated with the PBN,SBN, GNP, SNP of MCP (Longjing 20)and FEP(Longjing 21). The effects of row spacing on PBN were larger than on SBN in MCP, but smaller than on SBN in FEP. When row spacing was becoming larger, the SSRSB and GNP of two varieties were getting lower, while the SNP and GNP were getting higher. The yield of Longjing 20 (8 109.7 kg · hm-2)was the lowest when row spacing was 21 cm, because the space was too small for the plants to grow at latemid stage and the intensive competition suppressed the SNP. Due to the narrower row spacing, higher density at 18 cm row spacing, the tillering ability was suppressed in the early stage, the superiority place of tillering also played a role in yield formation, and the yield in 21 cm row spacing increased. All together,narrow row spacing was benef i cial to FEP, while wide row spacing was benef i cial to MCP.

Discussion

Rice has strong ability to adjust the structure of the population in fi eld. However, the ability varies among different plant types of varieties. The determination of the rice planting density should depend on the types of the varieties. The planting density could be adjusted by both hole-spacing and row spacing. Upto-date, most of the studies about the planting density of rice are carried out on the fi xed row spacing. Dryraising and sparse technology is adopted for the rice production in the cold region, in which hole spacing is 10.0-13.2 cm and row spacing is 30 cm. All types of rice adopted one pattern of the density combination would be harmful for enhancement of yield. Row spacing should be widened to activate the tillering ability of rice. Using the row spacing to improve the space utilization in the middle and later growth periods in fi eld accelerates the absorption and assimilation of the solar energy and the formation of yield.

Some research pointed that expanding row spacing appropriately improve the structure of the population and seed setting rate of panicle (SSRP)of rice (Chen et al., 2005; Amano et al., 1993). The stem number per square meter was getting lower as the row-holespacing becoming wider (Xia et al., 2006). In this study, SSRP in both types of rice varieties were improved by adjusting the row spacing. But the theoretical criteria for row spacing to reach the highest SSRP were different, 22.0 cm for Longjing 20 and 25.7 cm for Longjing 21. As the row spacing increased from 18 cm to 33 cm, the stem number per square meter increased first and reduced afterward. The highest stem number per square meter of the two types of rice varieties was obtained when row spacing was 24 cm.The suitable row spacing is benef i cial not only to the morphological characteristics of stems, but to the plant physiological characteristics and lodging resistance as well (Xie et al., 2003). Narrowed row spacing reduces the stem interval and improves the width of stem internode (Yan et al. 2007). Consistent with the previous results, row spacing had more effects on the width of the basal internode in MCP (Longjing 20)than that in FEP (Longjing 21). The components of yield formation and the morphological traits in MCP(Longjing 20)were more sensitive to the row spacing than that in the FEP (Longjing 21). Larger row spacing activated the ability of tilering in MCP and elevated the number of productive panicle to improve the yield. But for the insensitive variety (Longjing 21),narrowed row spacing should be adopted to avoid the weakness of less tillers and take advantages of grain weight and grain number to improve the yield.Therefore, it's necessary to select cultivation modes of different types. For a long time, rice usually adopts the transplanting with fi xed spaced in cold region, so the cultivation mode of different types of rice should go with the agricultural implements improvement together.

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