EVALUATION OF PHYSIOLOGICAL GROWTH PARAMETERS OF MAIZE IN MAIZE-LEGUME INTERCROPPING SYSTEM.
Field trial was conducted in 2011/2012 and 2012/2013 to determine the maize growth parameters under maize-soybean and maize-cowpea intercropping system at different reproductive stages. The varieties used were Umut 2002 (soybean), Karagoz (cowpea) and PR31G98 (maize) while the cropping treatments were sole and intercrop (alternate-rows). The experimental design was a randomized complete block design with three replicates. Results showed that maize planted (alternate-rows) simultaneously with cowpea and soybean recorded significantly higher values of leaf area index (LAI), leaf area ratio (LAR) and net assimilation rate (NAR). Highest values of NAR was recorded at R1 stage; LAI, LAR and relative growth rate (RGR) through at vegetative growth stage. LAI (sole maize) and NAR (1M+1C) showed significant correlation with grain yield. LAR and RGR for maize decreased from VT to R6. The LAI and NAR at silking stage have been identified as the major determinants of grain yield.
Key words: Alternate intercropping, cowpea, LAI, RGR, soybean.
Intercropping is termed the growing of two or more crops simultaneously on the same field. The main purpose of intercropping is to increase productivity and ensure the effective land use. The common crop combinations in intercropping systems are cereal with an adventitious root system and legume with a deep tap root system (Matusso et al. 2012). In a cereal-legume intercropping system, however, an increase in cereal and a decrease in legume intercrop yield is frequently stated. Difference in the pattern and spatial extension of root growth is one of the significant factors determining the relative success of the two crops that are grown together. In spatial arrangements, component crops compete for light, water, carbon dioxide and nutrients etc. It was reported that intercropping is a safer and more stable system of agricultural production than sole cropping for small farms, where capital is limited and labor is available (Guvenc and Yildirim, 1999).
Cereals generally have much greater rooting densities making them more competitive with respect to uptake of nutrients from the rhizosphere.
Besides the difference in rooting characteristics, the interference of one crop species with another when grown together is also a common observation. These effects are attributed to allelochemicals especially phenolic compounds that are released from the actively growing as well as decaying plant residues (Gill et al. 2009).
The common examples are maize with cowpea, soybean, groundnuts and beans, sorghum-cowpea, millet- groundnuts, and rice-pulses in intercrooping systems (Matusso et al. 2012). Intercropping causes effective usage of sunlight, nutrient and water, as well as, minimizing risk of pests and diseases (Brintha and Seran, 2009). But, spatial distribution in the field is great significance because it influences the efficiency with solar radiation and space are utilized.
Crop growth indices such as leaf area index (LAI), net assimilation rate (NAR), relative growth rate (RGR) and leaf area ratio (LAR) are important traits in crop physiology. These parameters could be associated with crop growth and competition in intercropping (Olasantan et al. 1996). Ozalkan et al. (2010) indicated that LAI and CGR at flowering stage have been identified as the major determinants of yield.
The aim of intercropping is to produce advantageous biological interactions between the crops. Because of the maize is a widely used crop, inter-row space could advantageous be used for legumes in the intercrop systems. This is an-old practice which has drawn the attention of the whole world because of its yield advantages. Most of the researchers were studied relationships between growth parameters and grain yield during vejetative and beginning of reproductive stages (Flores-Sanchez et al. 2013). Unfortunately, there are scarcity about growth parameters related to intercropping system observed different reproductive stages such as tasseling, blister, kernel dough and physiological maturity of maize. That is why the present study was conducted to determine the maize growth parameters, interrelation of parameters and their relation with grain yield.
MATERIALS AND METHODS
Experimental design: The field experiments were conducted at the Research Field of the Faculty of Agriculture, Adnan Menderes University, Aydin-Turkey in 2011-2012 and 2012-2013. The area is characterized with sandy loam soil and 7.6 pH. Maize cultivar (PR31G98), soybean seed (Umut 2002) and cowpea seed (Karagoz) were used in this study. Each plot was 5 m long sown by planter in four rows. None of the legume seeds were inoculated with Rhizobium. The experimental layout was randomized complete block design with three replications as follows:
(i) (1M:1S): There were four rows of maize planted at spacing of 70x20 cm and between every two rows; a row of soybean was placed at 35 cm from maize rows.
(ii) (1M:1C): There were four rows of maize planted at spacing of 70x20 cm and between every two rows; a row of cowpea was placed at 35 cm from maize rows.
(iii) Sole maize: There were four rows of maize planted at spacing of 70x20cm.
(iv) Sole legumes: There were four rows of legumes planted at spacing of 35x5cm.
Cultural practices: Sowing was done between 18/05/2011 and 03/05/2012. The 2011/12 and 2012/13 growing seasons. During the field experiments from May to September the average air temperatures, precipitation and relative humidity and long term (1954-2013) values were given at Table 1. Irrigation of crops was simultaneously during the third week of June. The other applications were repeated every 10 days during the period of the trial. Fertilizers were applied only to maize. The 15-15-15 NPK fertilizer was applied at the rate of 30 kg per hectare at sowing and urea at 12 kg per hectare as top dressed at six weeks after sowing.
Physiological growth parameters: In a crop the growth parameters i.e. CGR (crop growth ratio), RGR, NAR and LAI have been identified as the major determinants of yield. A combination of these parameters clarify different yields better than any individual growth variable (Liu and Wiatrak, 2011). So these growth indices were used at research. LAI, RGR and NAR were calculated using established formulae (Hunt et al. 2002) and LAR (Ennin et al. 2013), shown below.
- Leaf area index (LAI) = L / A (L=Leaf Area, A=Ground Area)
- Net Assimilation Rate (NAR) = 1 / L*dw / dt (L=Leaf Area, dw=Dry Weight Production in t Days, dt=Number of Days)
- Leaf Area Ratio (LAR) = L / W (L=Leaf Area, W=Dry Weight)
- Relative Growth Rate (RGR) = 1 / W * dw / dt (W=Dry Weight, dw=Dry Weight Production in t Days, dt=Number of Days)
Reproductive stages of maize were defined when at least 50% of the plants have reached that stage. Growth indices for maize were measured at VT (Tasseling), R1 (Silking), R2 (Kernel Blister), R3 (Kernel Milk), R4 (Kernel Dough), R5 (Kernel Dent) and R6 (Physiological Maturity) (Anonymous, 1993). Correleations between maize grain yield and growth indices were measured at R6 (Physiological Maturity) stage.
Statistical analysis: Variance analysis and correlation coefficient were statistically analyzed with the SPSS (1999). Probabilities equal to or <0.05 were considered significant. Differences between treatments were evaluated with LSD test.
Leaf area index (LAI) (m2 m-2): LAI is a indication of leafiness per unit ground area and determines the rate of dry matter production. LAI was positively influenced by intercropping pattern. Results of variance analysis showed that differences between growth stages in terms of the LAI and between intercropping patterns were significant (Figure 1). The variation in LAI values of both years might be due to the fluctuation in rainfall because water stress leads to rapid leaf senescence and to reduction in the LAI. The highest LAI of maize was recorded with intercropping and values were decreased with crop growth period progresses. In this study a range of 4.55 to 3.58 m2 m-2 was recorded for 1M+1C intercropping depending on time. The highest (4.55 m2 m- 2 and 4.72 m2 m-2) and the lowest (3.20 m2 m-2 and 3.25 m2 m-2) leaf area index were observed with 1M+1C and control, respectively in 2011/2012 and 2012/2013.
Leaf area ratio (LAR) (m2 kg-1): Leaf area ratio is the ratio of leaf area to the dry weight. Data on LAR of maize was affected by crop growth stage and intercropping pattern. Figure 2 showed that LAR values were positively affected by intercropping. Results of variance showed that there was a significant difference between crop growth stages in terms of the leaf area ratio (LAR).
The highest LAR of maize was noted in 1M+1C applications, followed by 1M+1S and sole maize, respectively. LAR decreased with increase in the growth stages of maize. The LAR values were changed from 3.54 m2 kg-1 (VT stage) to 0.84 m2 kg-1 (R6 stage) for sole maize in 2011/12. Second year the values were changed from 3.70 m2 kg-1 to 0.86 m2 kg-1 depending on the growth stages.
Net assimilation rate (NAR) (g m2 day-1): Net assimilation rate is a great physiological characteristics of a crop plant identifying its yield, and is thus great agricultural importance. Results of variance analysis indicated difference between growth stages in terms of NAR was significant, and difference between intercropping treatments was significant. Data related to NAR of maize as affected by year, crop growth period and intercropping (Figure 3). The highest NAR of maize obtained from silking and kernel blister stage respectively. During the R1 stage, there was a increase in NAR. The values were changed from 0.9-24.0 g m2 day-1 in 2011/12 and 1.0-26.2 g m2 day-1 in 2012/2013.
Relative growth rate (RGR) (kg kg day-1): Relative growth rate is a measure used to quantify the speed of crop growth. RGR values influenced by reproductive stage growth and intercropping. The highest RGR of maize obtained from the growth stage of tasseling and sole cropped of maize. RGR values were decreased after growth of blister stage (Figure 4). Values for maize significantly reduced with maize aged and the highest values were obtained from intercropping systems.
Correlation among variables: In our study, it was determined the correlation coefficients between growth parameters and grain yield in all reproductive stages. The correlation between different growth parameters and grain yield at R6 stage were shown in Table 2. Correlation data showed a significant and positive correlations (r=0.919) between NAR and RGR at 1M+1S treatment. Data revealed that GY in maize was positively and significantly related to LAI (sole maize) and NAR (1M+1C). In the experiment grain yield was significantly negative correlated with LAR (r=0.880) at 1M+1S treatments. Also among the growth parameters LAR and LAI (sole maize and 1M+1S treatments), NAR and LAI (1M+1S) and NAR and RGR (sole maize) there were found positive correlations. This study showed that the effects of crop arrangement such as sole crops and maize/legume (soybean and cowpea) intercropping on growth parameters of maize were significant.
From the results the conclusions can be summerized as follows; the intercropping system (maize/soybean, maize/cowpea) positively affected the LAI, LAR and NAR of maize. When maize was intercropped simultaneously with soybean or cowpea, growth of maize in terms of the measured parameters was higher than when it was planted as sole crop. Intercropping cannot be considered homogeneous within layers of the canopy. These systems must contain widely spaced strips of a tall species. Similarly, spatial distribution in the field is of great importance when intercropping two or more species, since it effects the efficiency with which solar radiation and space are used. To sum up, LAI and NAR revealed most effective to grain yield. It is further concluded that NAR was the major contributor towards grain yield because this character had high positive correlation, thus it should be evaluated as major concern in increasing grain yield and quality of maize in maize/cowpea intercropping system.
Table 1. Monthly average temperatures, precipitations and relative humidity
Month###Temperature (degC)###Precipitation (mm)###Relative humidity (%)
Table 2. Correlation among grain yield and some physiological growth parameters at different intercropping treatments at physiological maturity stage (R6).
###1M+1C###0.255 ns###0.748 ns
###1M+1C###0.847*###0.380 ns###0.778 ns
###1M+1S###-0.806 ns###0.904*###0.403 ns
RGR###M###-0.373 ns###-0.722 ns###-0.645 ns###0.892*
###1M+1C###0.692 ns###0.173 ns###-0.134 ns###0.678 ns
###1M+1S###-0.548 ns###0.723 ns###0.515 ns###0.919**
It was found that all intercropping treatments had greater indices of leaf area in comparison with sole cropping systems. Brintha and Seran (2009) obtained that an increase in LAI with all intercropping treatments. Similarly, Matusso et al. (2012) who observed a gradual increase in LAI from the vegetative growth stage to the reproductive stage and thereafter it declined. On the other hand, among intercropping systems, Choudhary et al. (2014) stated that a decrease in LAI of maize when it was intercropped with vegetables (radish, spinach, carrot) over sole cropping. In intercropping systems, the reductions of maize LAI have been also revealed by other researchers (Makinde et al. 2009).
Our research is in confirmity with the findings of Famaye (2003) who stated that LAR decreased as coffee seedlings aged and intercropping coffee with plantain improved its physiological growth than when grown as sole crop. Higher LAR values under soybean-maize intercropping compared to sole cropping were reported by Ennin et al. (2013). Similar findings of Pasari et al. (2002) reported that the LAR value of intercropping treatments was more than sole crop of soybean. With the increasing leaf senescence which has less leaf area for photosynthesis, the LAR values were declined (Asafu- Agyei et al. 2000). This is consistent with results of a a study conducted by Taguiang (1989) who reported that corn/mungbean, corn/rice, corn/sugarcane intercrops increased LAR values.
Sabaruddin et al. (2013) indicated that the leaves of a crop unshaded by their neighbouring plant canopy were exposed to sunlight which raised their NAR. On the other hand Weber et al. (1978) stated that no difference in the NAR of corn and rice when grown as sole crops or as intercrops.
Crop forage yield and RGR were reduced with intercropping compared with sole crop (Elfeel et al. 2013). Pandey and Singh (2015) stated that RGR values in wheat was initially high but with time it decreases and much of the decrease would be attributed to an increase of shading.
Daur et al. (2011) found that among the growth parameters, biomass and LAI showed the highest significant correlation with grain yield. Similar findings of Ozalkan et al. (2010) stated that the highest LAI was recorded during linear growth stage and during flower stage. Grain yield was significantly positive correlated with LAI. Abayomi and Fagbenja (2005) stated that NAR, CGR and RGR were positively associated with grain yield while LAR showed negative relationship. The positive and significant correlation coefficient some between growth parameters and grain yield explains the true relationship between the parameters and direct selection through this trait will be effective, thus direct selection for these characters should be major concern for plant breeder.
This study showed that the roles of crop arrangement on growth and development of maize as sole crops and maize/legume (soybean, cowpea) intercropping. From the results the following conclusions can be drawn. The intercropping system (maize/soybean, maize/cowpea) positively affected the LAI, LAR and NAR of maize. When maize was intercropped simultaneously with soybean or cowpea, growth of maize in terms of the measured parameters was higher than when it was planted as sole crop. Intercropping cannot be considered homogeneous within layers of the canopy. These systems must contain widely spaced strips of a tall species. Similarly, spatial distribution in the field is of great importance when intercropping two or more species, since it effects the efficiency with which solar radiation and space are used. In conclusion, LAI (sole maize) and NAR (1M+1C) revealed most effective to grain yield.
It is further concluded that NAR was the major contributor towards grain yield because this character had high positive correlation with yield, thus it should be evaluated as major concern in increasing grain yield and quality of maize in maize/cowpea intercropping system.
Acknowledgements: We thank the Projects of Scientific Investigation of Adnan Menderes University for funding (Project number: KOMYO11001).
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