Maize Yields Performance in Strip Planting Patterns with Two Plant Densities

The Huang-Huai-Hai Plain is the most important maize production region in China. To further investigate the improvement of maize yield by changing the planting pattern combined with two plant densities in this region, field experiments involving four planting patterns (three-row strip, four-row strip, five-row strip and a conventional uniform row spacing pattern (the control) under two plant densities (67,500 and 82,500 plants/ha) were conducted in 2011 and 2012. Only the plant density, not the planting pattern, significantly influenced the leaf area index at R1 stage and the total leaf area duration. The radiation use efficiency and the above-ground biomass at R5 were both higher under the three strip planting patterns than under the control, but the differences were not statistically significant. The effects of the planting patterns on the grain yield were significant in both years and the yields were 16.7, 6.1 and 10.7%, respectively higher in 2011 and 17.2, 12.1 and 10.6%, respectively higher in 2012 under the three-, fourand five-row strip treatments, respectively, compared with the control. However, grain yield was affected by neither plant density nor the interaction between planting pattern and plant density. Therefore, optimal strip planting pattern could not be better estimated by considering plant density.


INTRODUCTION
Maize (Zea mays L.) is important as a staple food for human, as feed for livestock and as a raw material for many industrial products, especially in developing countries.However, in recent years, in addition to global warming, extreme weather has frequently occurred during the maize growing season.These extreme weather events increase the risk of reduced output under the traditional planting patterns for summer maize, especially with increased plant density.The Huang-Huai-Hai Plain is the most important winter wheat and maize production region in China and makes up 1/6 of the total cultivated land area in China.In this area, during the pollination period of summer maize, heat waves and overcast or rainy weather occur frequently (Li et al., 2005(Li et al., , 2008;;Zhou et al., 2008), which negatively affects pollination and causes successfully pollinated kernels to abort, resulting in yield loss.Therefore, more research is required to find new technologies, including cultivation methods, to adapt to the impact of climatic variability on maize production.
Crop row spacing influences the canopy architecture, a distinguishing characteristic that affects the utilization of light, water and nutrients (Sharratt and McWilliams, 2005).Row spacing also affects the exploitation of the photosphere and rhizosphere by the plants, especially when the plants are too close to each other.A proper plant spacing is necessary for optimum yield (Obi, 1991).Optimal row spacing can improve group structure, reduce competition between strains and promote the development of individual growth, increasing the root number, leaf area and above-ground biomass (Wu et al., 2005).The above-ground biomass and yields were significantly affected by the planting patterns in maize hybrids (Yilmaz et al., 2008).
In our previous research, the above-ground biomass and grain yield were increased by using three new strip planting patterns (three-row strip, four-row strip, five-row strip) compared with the conventional uniform row spacing pattern (Zhang et al., 2012a, b).Under medium planting density (67,500 plants/ha), the grain yield increased by 10.58, 6.54 and 12.06%, respectively under the three-, four-and five-row strip treatments, respectively, compared with the control.Planting patterns response models might be further improved by considering the effects of plant density.
This study was conducted to test the hypothesis for corn production in the Huang-Huai-Hai Plain, Eastern China: yield increases with the strip planting patterns are greater with high plant density beyond 67,500 plants/ha.This paper reports our study on the aboveground biomass and grain yield in summer maize in the   Huang-Huai-Hai Plain of China as a further step towards understanding the effect of planting patterns combined with plant density on plant growth, as measured by the leaf area index, leaf area duration, above-ground biomass, radiation use efficiency, yield and yield components of the maize.

Site description and soil properties:
Field experiments were conducted in 2011 and 2012 at the Research Farm of Qingdao Agricultural University, Jiaozhou Experiment Station (36°15'52''N, 120°01'41''E), Qingdao, China.The total rainfall during the maize growing season was 554 mm in 2011 and 394 mm in 2012.During the same period, the total sunshine was 527.8 h in 2011 and 679.7 h in 2012.The previous crop was winter wheat; maize was shown on June 29, 2011 and June 26, 2012 and harvested on October 12, 2011 and October 9, 2012, (total 105 days in both years).The maize cultivar was 'Zhengdan' 958, which is popular in the local area.During the growing seasons of summer maize, a light irrigation was given on June 30 in 2011 and June 28, 2012 after planting and no additional irrigation was given for either year.The soil at the experimental site was fluvo-acqui soil with a pH of 6.88; the organic matter concentration was 6.75 g/kg, the available nitrogen (alkali hydrolysable N) was 84.00 mg/kg, the available Phosphorus (P) was 69.25 mg/kg and the available potassium (K) was 86.82 mg/kg (Table 1).

Experimental details:
The experiment was conducted as a two-factor split-plot design with three replications.The main factor was the planting pattern, with four planting patterns (three-row strip, four-row strip, fiverow strip and a conventional uniform row spacing pattern) and the split factor was plant density (67,500 and 82,500 plants/ha).The plot size was 6.5×11.0m (71.5 m 2 ).Slow-release fertilizer (Kingenta Company, China, N-P 2 O 5 -K 2 O: 22-8-12) was applied with 750 kg/ha as the basal application and no top-dressing during the growing season.The planting patterns and the space between two adjacent maize were shown in Fig. 1.
The above-ground biomass and leaf area were measured at 53 (R1 stage) and 105 (R5 stage) Days after Sowing (DAS) in 2011 and at 57 (R1 stage) and 105 (R5 stage) DAS in 2012.Three, four, five and three plants, respectively, (corresponding to the number of rows) were sampled from each subplot of the three-, four-and five-row strip arrangement and the conventional uniform row spacing planting pattern.The samples were dried at 105° for 30 min and then at 80° to dry till constant dry mass.
The total solar radiation was calculated from the weather data (from local weather forecast station) as: where, Q 0 = The daily solar radiation S = The real sunshine hours S 0 = The theoretical sunshine hours S/S 0 = The percentage of sunshine a and b = Coefficients (Zuo et al., 1963) The calorific value of maize is 18.07 kJ/kg (Lin et al., 2000;Xu et al., 2002) and the intercepted Photosynthetically Active Radiation (PAR) is computed as 0.45 of the incoming solar radiation (Kiniry et al., 1998).Thus, the Radiation Use Efficiency (RUE) (%) was calculated as: Unit area of biomass above ground (kg/m 2 ) ×18.07 (kJ/kg) / (Q (kJ/m 2 ) ×0.45) ×100 (2) The leaf area (m 2 ) was calculated as: where, L = Maximum length of leaf W = Maximum width of leaf K = Adjustment factor (0.75) The leaf area index was calculated as suggested by Sestak et al. (1971): The Leaf Area Duration (LAD) was calculated by adopting the formula of Power et al. (1967) and expressed in terms of days as: where, L 1 = The leaf area index at time t 1 L 2 = The leaf area index at time t 2 t 2 -t 1 = The time interval in days between the two stages The percentage of barren stalks was calculated as: Percentage of barren stalks (%) = Number of barren stalks*100/Total number of plants ( 6) The Harvest Index (HI) was calculated as: HI = Grain yield (kg/ha) /Total biomass yield (kg/ha) (7) At R5 stage (105 days after sowing) in 2011 and 2012, the plants in the middle two zones of each plot were sampled to measure the total biomass and grain yield.In the harvest area, the number of plants and barren stalks (no ear or no grain-bearing ears) were both counted and recorded for the calculation of percentage of barren stalks.Twenty ears were selected to determine the components of yield, such as number of kernel rows per ear, number of kernels per row and 100-kernel weight.

Statistical analysis:
The data were analyzed using standard Analysis of Variance (ANOVA) and General Linear Model (GLM) procedures and the means were separated according to Fisher's protected Least Significant Difference (LSD) at p≤0.05 (SAS, 1996).

Leaf area duration:
The planting patterns had no significant effect on the Leaf Area Duration (LAD) of the maize in either year, except at 0-53 day (before R1 stage) in 2011, while the LAD was significantly greater for the high plant density than for the medium plant density during the whole development period in both years (Table 3).The pattern×density interactions were insignificant for both the LAD and the total LAD in both years.Among all treatments, the highest total LAD was recorded in the treatment of the four-row strip planting pattern with high plant density in 2011 and in the treatment of the three-row strip planting pattern with high plant density in 2012, while the lowest total LAD was recorded in the control planting pattern with medium plant density for both years.

Above-ground biomass:
The above-ground biomasses at R1 and R5 stage were less in 2012 than in 2011; however, the responses of above-ground biomass to the planting patterns and plant density were similar in 2011 and 2012 (Table 4).Among all the planting patterns, the average above-ground biomass of the three-row strip planting pattern was highest at both R1 and R5 stage in both years, while a significant difference existed only in the above-ground biomass at R1 stage in 2011 (p<0.05).The plant density significantly influenced the above-ground biomass at R1 stage in both years and at R5 stage only in 2012 and the aboveground biomass at both stages was generally greater for the higher plant density than for the medium density in both years.The planting pattern×plant density interactions were not significant for the plant aboveground biomass at either R1 or R5 stage in either year (Table 4).

Yield components:
No difference in the percentage of barren stalks was observed among the planting patterns in 2011, but a significant difference was observed in 2012 and the conventional uniform row spacing pattern (control) had the highest percentage of barren stalks in both years (Table 6 and 7).The pattern did not significantly influence the kernel number per row in either year or the 100-kernel weight or kernel weight per year in 2011.However, a significant difference in kernel number per row, 100-kernel weight and kernel weight per year was observed between the patterns in 2012.The lowest values for these parameters were recorded for the control planting pattern.The percentage of barren stalks was significantly influenced by the plant density only in 2011 and the percentage of barren stalks was greater for the high density treatment than for the medium density treatment.No significant difference in kernel number per row, 100-kernel weight, or kernel weight per year was observed between the densities for either year (Table 6 and 7).There was no significant pattern×density interaction for any of the yield component indices in either year except for the kernel number per row in 2012 (Table 6 and 7).

DISCUSSION
Leaf Area Index (LAI) is a key structural attribute for agricultural crops and is closely related to light interception, which determines biomass production (Monteith, 1977).Canopy photosynthesis increases with LAI (Rochette et al., 1995;Campbell et al., 2001).Leaf area is influenced by genotype, plant population, climate and soil fertility (Valadabadi and Farahani, 2010), however, leaf area is not significantly affected by the plant spacing (Ibeawuchi et al., 2008).On the other hand, the LAI varies depending on a number of factors, including seasonal climate, water and nitrogen availability (Ewert, 2004).We found no significant difference in the LAI between the planting patterns (Table 2).The LAI was significantly influenced by the plant density but only at R1 stage and generally increased with increasing plant density.These findings are consistent with Ferreira and Abreu (2001) and Saberali et al. (2007).The Leaf Area Duration (LAD) shows an integrated lasting time of assimilation surface (Beadle, 1993); a higher leaf area index leads to increased leaf area duration (Shivamurthy, 2005).The LAD also determines the extent of the above-ground biomass production (Krishnamurthy et al., 1973); the LAD during the period of generative organ formation has a great impact on productivity (Gawrońska, 1980).In this research, the LAD was also significantly influenced by the plant density, not the planting patterns or the interaction between plant density and planting patterns (Table 3).
Radiation Use Efficiency (RUE) is the key factor determining crop yield and is related to crop biomass (Huang et al., 2007;Miranzadeh et al., 2011).The planting patterns did affect the RUE (Tollenaar and Aguilera, 1992) and the high density may also improve it (Sangoi et al., 2002).Although the RUE was not significantly influenced by the planting patterns in either year, the RUE increased under those three strip planting patterns (i.e., three-row strip, four-row strip, five-row strip) compared with that under the control (uniform row spacing pattern) and the average values of the biomass were also higher for the three strip planting patterns than for the control, although the difference did not reach the significant level (Table 4 and 5).
Grain yield and HI can be increased by enhanced plant spacing precision or density (Doerge et al., 2002;Andrade et al., 2002;Gozubenli et al., 2004;Sharratt and McWilliams, 2005;Yilmaz et al., 2008).The HI was not significantly influenced by either the planting pattern or the density, while the planting patterns significantly affected the grain yield (Table 5) and the three-row strip pattern showed the highest yield in both years (Table 5), which is consistent with our former report (Zhang et al., 2012a).The percentage of barren stalks of the three strip planting patterns (Table 6 and 7) are consistent with our previous report and it might be because that leaf angles above the ear became more upright allowing greater light penetration into the canopy in strip planting patterns, especially in threerow strip pattern (Zhang et al., 2012b).Among all treatments, the highest grain yield was obtained from the three-row strip planting pattern with high plant density (82,500 plants/ha) in both 2011 and 2012.It was found that the photosynthesis of the two leaves above the ear was highest in three-row strip planting pattern, which contribute greatly to grain filling and the kernel weight per year (Zhang et al., 2012b).However, the interaction between planting pattern and plant density was insignificant.In addition, the yields and harvest index were not high for either years, which was mainly due to late planting in both years and unfavorable weather, such as low temperature and less sunshine during grain filling period in 2011 and over raining at the early grain filling in 2012 (Table 1).
This research tested the hypothesis and the result was that strip plant patterns, especially three-row strip planting pattern indeed could increase grain yield, however, the effect of the interaction between planting pattern and plant density on yield was not statistically significant, in other words, yield response to strip planting patterns was not greater with increased plant density, therefore, plant density need not be considered in the estimation of optimum strip planting pattern.

ACKNOWLEDGMENT
This study was partially funded by the Major Innovation Project for Applied Technology of Shandong Province; The National Key Technology R and D Program (2011BAD09B01-2); Modern

Fig. 1 :
Fig. 1: Graphical representation of the planting patterns (row and broadband spacing) (a) conventional uniform row spacing planting pattern (control): equal row spacing (70 cm), the plant spacing was 21.2 and 17.3 cm under 67,500 and 82,500 plants/ha, respectively, (b) threerow strip planting pattern: two equal row spacing (55 cm) and a broadband (100 cm), the plant spacing was 21.2 and 17.3 cm under 67,500 and 82,500 plants/ha, respectively, (c) four-row strip planting pattern: three equal row spacing (55 cm) and a broadband (120 cm), the plant spacing was 20.8 and 17.0 cm under 67,500 and 82,500 plants/ha, respectively, (d) five-row strip planting pattern: four equal row spacing (55 cm) and a broadband (140 cm), the plant spacing was 20.6 and 16.8 cm under 67,500 and 82,500 plants/ha, respectively

Table 1 :
Some climatological data of experimental site during maize growing seasons in 2011 and 2012 (meteorology station of Qingdao)

Table 2 :
Leaf Area Index (LAI) at R1 and R5 stages in maize affected by planting patterns and plant densities in years 2011 and 2012

Table 3 :
Leaf Area Duration (LAD) of summer maize with different planting patterns and densities in years 2011 and 2012 *: Significant at 0.05 probability level; ns: Not significant

Table 4 :
Above-ground biomass of maize with different planting patterns and densities at R1 and R5 stage

Table 5 :
Yield, harvest index and radiation use efficiency of summer maize with different planting patterns and densities at R5 stage

Table 6 :
Yield components of summer maize with different planting patterns and densities at R5 stage(2011)

Table 7 :
Yield components of summer maize with different planting patterns and densities at R5 stage(2012)