Determination of optimal strip width in strip intercropping of maize (Zea mays L.) and bean (Phaseolus vulgaris L.) in Northeast Iran

Journal of Cleaner Production xxx (2014) 1e8

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Determination of optimal strip width in strip intercropping of maize (Zea mays L.) and bean (Phaseolus vulgaris L.) in Northeast Iran Mehdi Nassiri Mahallati a, Alireza Koocheki a, Farzad Mondani b, *, Hassan Feizi c, Shahram Amirmoradi a a b c

Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran Department of Agronomy and Plant Breeding, Campus of Agriculture & Natural Resources, Razi University, Kermanshah, Iran Saffron Institute, University of Torbat-e-Heydarieh, Torbat-e-Heydarieh, Iran

a r t i c l e i n f o

a b s t r a c t

Article history: Received 29 December 2013 Received in revised form 14 October 2014 Accepted 30 October 2014 Available online xxx

Intercropping is a sustainable method for crop production used to maximize utilization of available resources. The aim of this study, conducted in 2009 and 2010, was to determine an optimal strip width in maize/bean strip intercropping. Treatments evaluated in the study were contribution of different strip width and intercrops of 2 rows bean and 2 rows maize (II), 3 rows bean and 3 rows maize (III), 4 rows bean and 4 rows maize (IV), 5 rows bean and 5 rows maize (V), maize and bean monocultures. The higher than average temperature in 2010, led to decrease crop yields in that year. The climatic conditions had more effect on reduction of bean yield than maize. Radiation absorption, radiation use efficiency, biological yield, land equivalent ratio, crowding coefficient and system productivity index were greater in 2009 than in 2010. Radiation use efficiency for maize and bean were higher in 2009 than 2010 (8.9% and 17.6% respectively). The strip intercropping system enhanced radiation absorption, radiation use efficiency, biological yield, land equivalent ratio, crowding coefficient and system productivity index compared with the monoculture system. Increasing strip width from 2 to 5 rows resulted in a decrease all the criteria measured. The best strip width was with II and III strip intercropping treatments. Although biological yield in intercropping was less than in monoculture, total land productivity was improved by greater land equivalent ratio (1.39 and 1.37). This means that 39% and 37% more land was required for monoculture than intercropping to produce the same yields in 2009 and 2010, respectively. Therefore it was demonstrated that an intercropping system is more effective than a monoculture system in resource utilization. It also appears that equivalent row numbers of 3 and 4 for each crop in a strip manner is more promising in resource use than other combination of rows. © 2014 Elsevier Ltd. All rights reserved.

Keywords: Radiation absorption Radiation use efficiency Temperature Land equivalent ratio Crowding coefficient System productivity index

1. Introduction Modernize crop production systems has already explored many methods to gain high yields. Most of these methods involved raising the use efficiency resources such as water and nutrients, land, solar radiation and atmospheric CO2. Due to utilization many of these resources are becoming limited, which is a drawback for more crop production (Awal et al., 2006). Therefore, sustainable methods of resource use are needed to enhance productivity of these resources under such limitations. Intercropping system has been considered as a method in which resources can be utilized

* Corresponding author. Tel.: þ98 9173017201; fax: þ98 8318321083. E-mail address: [email protected] (F. Mondani).

more efficient (Rodrigo et al., 2001; Willey, 1990) consequently improving plant production (Li et al., 2001; Tsubo and Walker, 2002; Awal et al., 2006; Zhang et al., 2007). Moreover, this system is a promising method to combine high productivity and ecological benefits that it could contribute to reduce the environmental impacts of agroecosystems such as climate change, acidification, terrestrial ecotoxicity or cumulative energy demand (Naudin et al., 2014). Many studies have revealed that intercropping systems could enhance interception of solar radiation and facilitate higher radiation use efficiency (Keating and Carberry, 1993). The extra solar energy used by an intercropping canopy can lead to improved crop production thus better economic yield (Awal et al., 2006). Radiation use efficiency (RUE) is a recognized valuation of the affect of biotic factors such as atmospheric water (Kiniry et al.,

http://dx.doi.org/10.1016/j.jclepro.2014.10.099 0959-6526/© 2014 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Nassiri Mahallati, M., et al., Determination of optimal strip width in strip intercropping of maize (Zea mays L.) and bean (Phaseolus vulgaris L.) in Northeast Iran, Journal of Cleaner Production (2014), http://dx.doi.org/10.1016/j.jclepro.2014.10.099

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1998), extremes of temperature and nutrient levels (Sinclair and Horie, 1989). Temperature changes have often been reported as a contributing factor to RUE variation (Sharpley and Williams, 1990). Furthermore, it is also assumed that RUE is independent of temperature (Sinclair and Mukhow, 1999). This assumption is usually made from experiments carried out under warm tropical environments. However, temperatures experienced in temperate environments are anticipated to influence canopy photosynthesis and as a result have a direct influence on RUE (Sands, 1996). Consideration of ways to enhance the efficiency of resources is growing in research on intercropping cereal crops. Intercropping cereals with legumes has been studied in the tropics (Tsubo et al., 2005) and rainfed areas of the world (Dhima et al., 2007). Maize (Zea mays L.) is potentially the most valuable source of plant fodder in many parts of world. In these cases common cropping system is one that combines maize with legume crops such as bean (Phaseolus vulgaris L.). The primary aim of a farmer is to produce a high yield from the maize crop and the secondary aim is to produce a better bean yield. Tsubo et al. (2005) stated that “Canopy structures and rooting systems of cereal crops are generally different from those of legume crops. In most cereals with legume intercropping, cereal crops form higher canopy structures than legume crops and the roots of cereal crops grow to a greater depth than those of legume crops. This suggests that the component crops may have differing spatial and temporal use of environmental resources”. Many investigations indicated that higher radiation use efficiency, nutrient use efficiency, and water use efficiency (Awal et al., 2006; Walker and Ogindo, 2003; Rowe et al., 2005) and higher yield (Tsubo and Walker, 2002) are demonstrated in intercropping systems compared to monoculture. Galka (2004) stated that essential changes must be introduced in agricultural practices with the realization of cleaner production methodology against the negative effect on the environment, particularly against soil and surface water pollution. Waste diminution practices should be introduced into agricultural sector and that could successfully protect the natural environment from pollution (Galka, 2004). We believe that employment of intercropping system also could help us to reduction of natural environment pollution. Incorporation of different crops leads to better utilization of resources such as water, nutrients and lights. This has been well documented in the literature (Willey, 1990 Rodrigo et al., 2001; Tsubo et al., 2005). High efficiency in resource utilization is actually the first step in transition to ecological and sustainable agriculture (Gliessman, 2007) and approaches such as alternatives for the use of inputs and finally redesign of a system in a sustainable manner are all complementary steps. Therefore intercropping systems in a manner to fulfill the present day technologies e.g. strip cropping seems to be a novel approach for low input sustainable agriculture. Although the intercropping systems have many advantages, nonetheless may incur management problems such as, use of machines and other inputs. Therefore one of the basic spatial arrangements used in intercropping is strip intercropping, which can be defined as a system of growing two or more crops together in strips wide enough to permit separate crop production using inputs but close enough for the crops to interact. Nevertheless, the current challenge is how to determine an optimal intercropping width to achieve the maximum crop productivity and resource use efficiency. The objectives of this study were (i) to evaluate radiation absorption and use efficiency in maize and bean strip intercropping (ii) to examine different competition indices and, (iii) to determine an optimal strip width for better management of resources to incur less competition among plants, and to induce higher productivity and sustainability.

2. Material and methods 2.1. Site description This study was conducted in 2009 and 2010 at the research farm Faculty of Agriculture, Ferdowsi University of Mashhad, Iran (latitude 36 , 150 N, longitude 56 , 280 E and altitude 985 m). The average annual rainfall is 278.6 mm and the long-term average air temperature is 12.4  C for the area. A composed soil sample was taken in before cultivation in depth of 0e30 cm at experimental site. Physical and chemical properties of the soil were determined in the Soil and Plant Analysis Laboratory (Table 1). 2.2. Experimental design The treatments were strip width, which included two rows of bean plus two rows of maize (II), three rows of bean plus three rows of maize (III), four rows of bean plus four rows of maize (IV), five rows of bean plus five rows of maize (V), and monocultures of maize and bean (Fig. 1). In each plot, distances between rows were 75 cm and 37.5 cm for maize and bean, respectively. Final plant density for monocultures of maize and bean were 11.1 and 14.3 plants per m2, respectively. The experiment was conducted in replacement series in which the proportion of maize to bean was 2:1 in each intercropping plot. Maize was considered as the main crop and bean as an intercrop companion crop. Plant varieties used in the experiment were Derakhshan for bean and single cross 704 for maize. The design was a randomized complete block with three replications. A plot size of 6  8 m was used. This experiment was conducted as a low input system. Farmyard manure was used for all treatments at 30 ton ha1. Moreover, in maize monoculture and bean treatments nitrogen fertilizer was applied at rates of 150 and 30 kg ha1, respectively. Pesticides, herbicides and fungicides for control of pests, diseases and weeds were not used during the growing seasons. Weeds were managed by hand weeding particularly in the early growing season. The experiment was planted on May 24 in 2009 and 2010, and harvested on September 3 in 2009, and on August 29 in 2010. Since maize was harvested as a forage plant, bean was also harvested before full maturation of seeds. Therefore, both maize and bean were considered as a forage crop with an emphasize on biological yield. 2.3. Data collection and analysis Randomized sampling was conducted 14 days after emergence (DAE) until harvesting. In each sampling, two plants (two plants of maize and two plants of bean) from each plot were randomly chosen and leaf area index and dry weight was evaluated. Leaf area index (LAI) was evaluated using a Leaf Area Meter (Li-Cor Model Li1300, USA, and Accuracy: 0.001 cm2). The samples were oven-dried at 70  C for 48 h, then weighed. Radiation use efficiency (RUE) was calculated on the basis of g MJ1 through the slope of linear regression between dry weight accumulation (gm2) and cumulative absorbed photosynthetically

Table 1 Physico-chemical properties of soil (0e30 cm) at the experimental site. Parameter

Value

Parameter

Value

Clay (%) Silt (%) Sand (%) pH (1:1:H2O) OC (%) Total N (%)

60.7 25.4 13.9 7.8 0.6 0.2

NO3eN (ppm) Available P (ppm) Available Na (meq/100 g) Available K (meq/100 g) Available Ca (meq/100 g) Available Mg (meq/100 g)

8.5 6.7 0.3 1.5 2.6 3.2

Please cite this article in press as: Nassiri Mahallati, M., et al., Determination of optimal strip width in strip intercropping of maize (Zea mays L.) and bean (Phaseolus vulgaris L.) in Northeast Iran, Journal of Cleaner Production (2014), http://dx.doi.org/10.1016/j.jclepro.2014.10.099

M. Nassiri Mahallati et al. / Journal of Cleaner Production xxx (2014) 1e8

II

III

3

V

IV

Fig. 1. Layout of maize/bean strip intercropping treatments: strip width of 2 rows bean and 2 rows maize (II), strip width of 3 rows bean and 3 rows maize (III), strip width of 4 rows bean and 4 rows maize (IV), strip width of 5 rows bean and 5 rows maize (V). The solid and dash lines are maize and bean, respectively.

active radiation (PAR) (Bange et al., 1997). In this study PAR absorption was considered as 50% of the total daily solar radiation. PAR absorption level was calculated using the following equations for maize and bean (Tsubo et al., 2005):

PARabs ¼ PAR0  ð1ePÞ*ð1  expðKm  LAIm Þ þ ðKB  LAIB ÞÞ (1) PARm ¼ PARabs  ðKm  LAIm Þ=ððKm  LAIm Þ þ ðKB  LAIB ÞÞ

PARB ¼ PARabs  PARm

LAI ¼

SPI ¼

(3)

where Sm and Sb are the mean yields of maize and bean in monoculture and Ym and Yb are the mean yields of maize and bean in intercropping, respectively.

(9)

2.4. Statistical analysis Data were subjected to analyses of variance for each component crop at 5% level of significance using SAS software. Standard error of means was used for treatment comparison. Slide Write and an Excel spread sheet were used for curve fitting and drawing the figures, respectively. 3. Results and discussion

(4)

2  1 þ exp ðxcÞ d

where a is the intercept, b is x value for maximum LAI (estimated from data), c is maximum LAI, d is the inflection point of LAI, and x is the time (DAE). The relative advantage of intercropping compared to monoculture was calculated for each proportion using total land equivalent ratio (LER) as:

  LER ¼ Yij Yii þ Yji Yjj

3.1. Temperature and radiation The average temperature during the growing season (MayeSeptember) was greater in 2010 than in 2009 by about 1.1  C (Table 2). Average maximum and minimum temperatures during growing seasons were greater in 2010 than in 2009 by about 1.9 and 0.3  C respectively. Night temperatures were cooler during the entire growing season of 2009. It seems that the lower temperature was more suitable for bean than maize in 2009. Hence 2009 was a

(5)

where Yii and Yjj denote yields of crops i and j in monoculture and Yij and Yji are the corresponding yields in intercrops. The competitive relationships between the two crops were determined using the crowding coefficient (K) values suggested by Willey (1979) as:

K ¼ Kab  Kba

(6)

Crowding coefficient of maizeðKab Þ ¼

Crowding coefficient of beanðKba Þ ¼

Sm Y þ Ym Sb b

(2)

where PARabs is absorbed radiation by intercropping canopy (MJ m2), PAR0 is total daily radiation (MJ m2) which was simulated by the method cited by Goudriaan and Van Laar (1993) for growing seasons of 2009 and 2010, P is reflection coefficient considered 0.08 for maize and bean, Km and KB are radiation extinction coefficients of maize (0.6) and bean (0.65), respectively. LAIm and LAIB are daily leaf area indexes of bean and maize, respectively. PARC and PARB are absorbed radiation by bean and maize, respectively. To calculate daily LAI the following equation was used (Loomis and Williams, 1963):

  a þ b  4$exp ðxcÞ d

In these equations, Yaa is the monoculture yield of maize, Ybb is the monoculture yield of bean, Yab is the intercropping yield of maize, Yba is the intercropping yield of bean, Zab is the sown proportion of maize, and Zba is the sown proportion of bean. Another index for assessing intercrops is the system productivity index (SPI), presented by Odo (1991) in the following equation, which standardizes the yield of the secondary crop, in terms of the primary crop:

Yab  Zba ðYaa  Yab Þ  Zab

Yba  Zab ðYbb  Yba Þ  Zba

(7)

(8)

Table 2 Monthly mean maximum and minimum temperatures during the growth seasons and the two-year average. Year

June

July

August

Total

33 34.7 33.8

33.3 35.5 34.4

19.8 18.3 19.1

19.1 19.5 19.3

26.4 26.5

26.2 27.5



Monthly average maximum temperature( C) 2009 31.6 35.3 2010 35.6 36.1 Two-year average 33.6 35.7  Monthly average minimum temperature( C) 2009 17 20.5 2010 19.3 20.8 Two-year average 18.1 20.6  Average maximum and minimum temperature( C) 2009 24.3 27.9 2010 27.5 28.4

Please cite this article in press as: Nassiri Mahallati, M., et al., Determination of optimal strip width in strip intercropping of maize (Zea mays L.) and bean (Phaseolus vulgaris L.) in Northeast Iran, Journal of Cleaner Production (2014), http://dx.doi.org/10.1016/j.jclepro.2014.10.099

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better year than 2010 for crop growth and development as reflected by the yields of both crops. Higher average temperature had more effect on reduction of bean yield than maize in 2010. Daily solar radiation levels during the growing seasons were similar in 2009 and 2010 (Fig. 2).

3.2. Radiation absorption

Fig. 2. Total daily solar radiation during growing seasons of 2009 and 2010.

Differences in radiation absorption for treatments were consistent over the 2 years. In the canopy of sole maize, the level of radiation absorption rapidly increased to a maximum on 63 and 59 DAE, at about 13.7 and 14.7 MJ m2 in 2009 and 2010, respectively (Fig. 3). It was nearly as high as that from 50 to 87 day after emergence (DAE) and 38 to 88 DAE in 2009 and 2010, respectively. Radiation absorption in the canopy of intercropped maize was lower than that in sole maize and it did not follow the same pattern. It increased rapidly to a maximum on 60 DAE, and remained almost constant until the end of the growing season in both years (Fig. 3).

Fig. 3. Radiation absorption maize and bean grown in strip intercropping during 2009 (left) and 2010 (right). Green, violet, and red lines shows radiation absorption by maize, bean, and intercropping canopy, respectively. Black line shows total daily solar radiation. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Please cite this article in press as: Nassiri Mahallati, M., et al., Determination of optimal strip width in strip intercropping of maize (Zea mays L.) and bean (Phaseolus vulgaris L.) in Northeast Iran, Journal of Cleaner Production (2014), http://dx.doi.org/10.1016/j.jclepro.2014.10.099

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5

Our results indicated that radiation absorption in the canopy of sole bean increased rapidly to a maximum on 60 and 55 DAE, at about 14.5 and 15.1 MJ m2, followed by a gradual decrease to about 5 and 7 MJ m2 until the end of the growing seasons in 2009 and 2010, respectively (Fig. 3). The level of radiation absorption in the canopy of intercropped bean was lower than that of sole bean but, followed the same pattern. It rapidly increased to a maximum on 51 and 47 DAE in 2009 and 2010 respectively, and then gradually decreased until the time of harvest (Fig. 3). Radiation absorption of intercropping canopies was higher than sole canopies in all strip intercropping treatments in both years (Fig. 3). Successive rows of bean occupied most of the inter row space of maize at the beginning and the middle of the development stage. It caused radiation absorption of strip intercropping treatments to be more than that of sole treatments. This indicated that the amount of radiation absorption by the canopy in strip intercropping was more than that in the canopy of sole crops. Willey (1990) concluded that radiation absorption in intercropping systems was about 30% more than in monoculture systems, implying enhanced efficiency of radiation in intercropping. Increasing strip width from 2 to 5 rows reduced radiation absorption by the canopy in intercropping crops, although it was greater than absorbed radiation by the canopy in the sole crops. Levels of radiation absorption by canopies of intercropping two rows of bean plus two rows of maize (II) and three rows of bean plus three rows of maize (III) were nearly more than other intercropping treatments in 2009 and 2010. In the treatments II and III the uncovered areas decreased resulting in a much smaller gap width and twice as many border rows were able to capture sideways incidental radiation (Zhang et al., 2007). Increasing strip width caused the canopy in intercropping to respond similarly to as the sole crops canopy. It is clear that competition for radiation played an important role in interspecific competition, in particular below a height of 40 cm, where bean dominated radiation interception. This competition for radiation probably had a larger effect on bean compared to maize during the growing season. Zhang et al. (2008) indicated that the relay intercropping of wheat and cotton increased the total absorption of radiation compared to monocultures of either crop.

soybean but the difference was not significant. Differences in conditions of experiments and the higher amount of nitrogen fixation by bean than soybean may be the reason for these contradictions. Averages RUE in strip intercropping treatments for bean were 1.03 and 0.86 g MJ1 in 2009 and 2010, respectively, which was 7.5% and 15% higher than that for bean monoculture. Since bean is a C3 crop, under low radiation intensity due to low photorespiration, its photosynthetic efficiency is more than under high radiation intensity. Therefore, it can be concluded that in strip intercropping, shading of maize on bean resulted in an increased share of radiation diffusion from total solar radiation and consequently improved RUE of bean. Strip intercropping system increased RUE in compared to maize and bean in monoculture, which led to increased biological yields. The findings of this study were similar to the results reported by Tsubo and Walker (2002) in maize with bean intercropping, and Awal et al. (2006) in maize with peanut intercropping. Gao et al. (2010) reported that RUE in soybean monoculture was less than that in intercropping, probably because of more efficient partitioning of material to pods with reduced radiation received by the intercropped soybean. Increasing strip width from 2 to 5 rows decreased RUE by 9.4% and 12.6% for maize and 20.2% and 32.3% for bean in 2009 and 2010, respectively. The RUE of maize in two rows of bean plus two rows of maize (II) and three rows of bean plus three rows of maize (III) treatments was higher than other strip intercropping treatments in both years, while it was higher only in two rows of bean plus two rows of maize treatment for bean in 2009 and 2010 (Fig. 4). The average temperature during the growing season was higher in 2010 than 2009 (Table 2). This may have contributed to reduce RUE. In other words, since bean is a C3 crop is more sensitive to warmer weather compared with maize which is a C4 crop and this may have caused greater reduction of RUE in bean. However, experimental evidence for a temperature dependence of RUE is still rare. Kumar et al. (1996), analyzed variability in RUE of castor beans in relation to climatic parameters and found a negative relationship between RUE and temperature. Moreover, Manderscheid et al. (2003) reported a significant negative relationship between RUE and temperature in the period before and during grain filling of wheat.

3.3. Radiation use efficiency

3.4. Biological yield

The RUE of maize and bean was estimated as the slope of a fitted linear relationship between intercepted PAR and dry weight for each treatments and each year. There were significant differences between treatments and years for RUE for each species. Average RUE of maize (1.79 and 1.63 g MJ1) and bean (1.02 and 0.84 g MJ1) in intercropping and monoculture systems was higher in 2009 than 2010, respectively (Fig. 4). It seems that higher temperature in 2010 compared with 2009 led to reduction of RUE via rising up maintenance respiration in both species. Averages RUE in strip intercropping treatments for maize were 1.82 and 1.67 g MJ1 in 2009 and 2010, respectively, which were 7% and 11.1% higher than that for maize monoculture. It is apparent that complementary effects of bean through the process of nitrogen fixation led to the supply of nutrients for maize. This is the reason for the increasing photosynthesis rate and greater dry matter production in maize resulting in better RUE in strip intercropping treatments compared to monoculture treatments. Legumes fix atmospheric nitrogen, which may be used by a host plant (Andrews, 1979). Nitrogen is emitted from the nodules into the soil where it can be used by other plants growing nearby. Moreover, N fixed by legumes can be transferred to intercropped crops during growing periods (Shen and Chu, 2004). Gao et al. (2010) reported that RUE for monoculture was greater than strip intercropping of maize with

Mean biological yields of each species were higher in 2009 than 2010 (Table 3). This may be due to lower than average temperatures in 2009 than 2010 and hence higher RUE and consequently higher biological yield in 2009. The higher average temperature in 2010 than in 2009 led to yield reduction of maize and bean. There were significant differences between treatments for biological yield in both crop species. Sole crop yields for both species were greater than respective yields in intercropping. Average biological yield of maize in intercropping for two years was 618.8 and 582.7 g m2, which was about 17.6% and 17.7% less than that in sole crop. Moreover, averages biological yield of bean in intercropping for the two years was 203.4 and 179.8 g m2, which was about 43.4% and 46.1% less than those in monoculture. Yields of maize with bean intercropping were higher by 9.5% and 9% in 2009 and 2010, respectively. This indicates that strip intercropping of maize with bean has an advantage in terms of yield. Crop yield improvement in intercropping systems compared to monoculture systems may be due to the better ability of the component species to absorb light and maximize the use of biophysical resources relative to crops grown separately under monoculture (Jahansooz et al., 2007). Intercropped maize and bean had higher RUE in comparison with monoculture of maize and bean leading to yield advantage of the intercropping system. This also

Please cite this article in press as: Nassiri Mahallati, M., et al., Determination of optimal strip width in strip intercropping of maize (Zea mays L.) and bean (Phaseolus vulgaris L.) in Northeast Iran, Journal of Cleaner Production (2014), http://dx.doi.org/10.1016/j.jclepro.2014.10.099

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Fig. 4. Radiation use efficiency of maize and bean in strip intercropping and monoculture treatments. Slope of dash and solid lines show RUE in 2009 and 2010, respectively. Blue squares and red triangles show cumulative dry weight for maize in 2009 and 2010, respectively. Green circles and violet stars show cumulative dry weight for bean in 2009 and 2010, respectively. In all of the strip intercropping treatments, LSD is 0.08 and 0.10 for maize and 0.10 and 0.16 for bean in 2009 and 2010, respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

could be due to the provision of nitrogen by bean for maize intercropped system. Li et al. (2006) indicated that intercropping maize with soybean led to increased grain yield. Increasing strip width from 2 to 5 rows decreased biological yield by 21.2% and 18% for maize and 23.8% and 17.8% for bean in 2009 and 2010, respectively. The biological yield of maize in treatments two rows of bean plus two rows of maize and three rows of bean plus three rows of maize were higher than other

intercropping treatments in 2009; while it was only higher in treatment two rows of bean plus two rows of maize in 2010 (Table 3). The biological yield of bean in treatment two rows of bean plus two rows of maize was higher than other intercropping treatments in 2009 and 2010. The average temperature during the growing season in 2009 was lower than in 2010 (Table 2). This condition was more suitable for bean than maize. In intercropping treatments shading of maize

Table 3 Effects of strip intercropping of corn and bean on biological yields (g m2) (BY) and land equivalent ratios (LER). Treatment

2009

2010

BY

II III IV V Sole Mean LSD

LER

BY

LER

Corn

Bean

Total

Corn

Bean

Total

Corn

Bean

Total

Corn

Bean

Total

697.4 645.2 581.0 549.9 750.6 644.9 52.9

250.9 191.5 179.8 191.2 359.3 234.6 44.2

948.4 836.8 760.8 741.1 750.6 821.9 72.9

0.93 0.86 0.77 0.73 e 0.82

0.70 0.53 0.50 0.53 e 0.57

1.63 1.39 1.27 1.26 e 1.39

646.6 609.0 545.2 530.1 699.8 606.2 31.4

209.6 171.9 165.4 172.3 333.2 210.5 14.6

856.2 780.9 710.6 702.4 699.8 762.5 55.9

0.92 0.87 0.78 0.76 e 0.83

0.63 0.52 0.50 0.52 e 0.54

1.55 1.39 1.28 1.27 e 1.37

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on bean reduced the temperature of the canopy. This event became more effective with narrower strip width. Therefore it appears that under unsuitable conditions an intercropping system is more effective than monoculture. This might indicate more efficient utilization of growth resources and thereby greater yield stability under unsuitable conditions by mixed cropping than monocropping (Agegnehu et al., 2006). Similarly, Tesfamichael and Reddy (1996) reported greater yield advantage by intercropping in a low rainfall area (unsuitable condition) than a medium rainfall area (suitable condition).

7

Table 4 Relative crowding coefficient (K) and system productivity index (SPI) of corn and bean grown in strip intercropping. Treatment

2009

2010

K value

II III IV V Mean

Corn

Bean

K

7.06 3.30 1.84 1.48 3.42

1.25 0.61 0.54 0.61 0.75

8.80 2.03 1.00 0.90 3.18

SPI

K value

SPI

Corn

Bean

K

1981.4 1748.2 1589.6 1548.4 1716.9

6.55 3.61 1.90 1.68 3.44

0.91 0.57 0.53 0.58 0.65

5.98 2.07 1.01 0.97 2.51

1798.1 1640.0 1492.3 1475.1 1601.4

3.5. Land use efficiency and competitive ability Land equivalent ratio (LER) varied between years and intercropping treatments. Total LER was higher in 2009 than 2010 (Table 3). Higher biological yield in 2009 in comparison with 2010 led to an increased LER. Average of partial LER in the strip intercropping treatments was 0.82 and 0.83 for maize and 0.57 and 0.54 for bean in 2009 and 2010, respectively. Although biological yields of the two crops in intercropping were less than those in monoculture, the intercropping improved total land productivity, as supported by greater LER (1.39 and 1.37 in average), which means that 39% and 37% more land was required in a monoculture system than intercropping for producing the same yields in 2009 and 2010, respectively. Partial LER decreased from 0.93 to 0.73 in 2009 and 0.92 to 0.76 in 2010 for maize when strip width increased from 2 to 5 rows. Moreover, partial LER decreased from 0.70 to 0.53 in 2009 and 0.63 to 0.52 in 2010 for bean when strip width increased from 2 to 5 rows. Higher total LER was obtained for the treatments two rows of bean plus two rows of maize and three rows of bean plus three rows of maize in 2009 and 2010, respectively (Table 3). LER showed a positive relationship with biological yields for the two component crops (Table 3). LER is reportedly an accurate reflection of the biological efficiency of an intercropping system. Values of LER greater than 1 are considered beneficial. Therefore, the strip intercropping of maize with bean system could improve land use efficiency considerably. As our results indicated, differences in radiation absorption were found between monoculture and strip intercropping treatments; however the higher RUE in intercrops can be held solely responsible for higher biological yields and consequently higher LER for maize and bean strip intercropping. Gao et al. (2010) reported that LER of an intercropping system was 1.19 in 2007 and 1.31 in 2008, pointing to a considerably greater land use efficiency of maize with soybean strip intercropping. Furthermore, advantages of wheat with chickpea intercropping system have been reported in other research (Banik et al., 2006). Our results indicated that the crowding coefficients (K) demonstrated difference between years and intercropping treatments. The average of crowding coefficient was higher for 2009 compared to 2010 (Table 4). It is indicated that strip intercropping for the year 2009 was more advantageous in comparison with the year 2010. The average of crowding coefficient for maize was higher than bean in both years. The crowding coefficient decreased from 8.80 to 0.90 in 2009 and 5.98 to 0.97 in 2010, when strip width increased from 2 to 5 rows. The highest crowding coefficients of 8.80 and 5.98 were obtained for the treatment two rows of bean plus two rows of maize in 2009 and 2010, respectively (Table 4). These crowding coefficient values indicated that maize was the dominant species in strip intercropping of maize with bean. The greater competitive ability of maize to exploit resources in association with bean has been reported by others (Li et al., 1999; Tsubo and Walker, 2002). It has been demonstrated that the advantages accrued from intercropping systems, in addition to the obvious benefit of competition in intercropping, is due to better utilization

of growth resources under the intercropping system of cereal with legume (Ofori and Stern, 1987). Banik et al. (2006) revealed that total productivity, land use efficiency and crowding coefficient were higher under intercropping of wheat with chickpea compared with monocultures of either species. Our results indicated that SPI was varied between years and intercropping treatments. SPI was higher for the year 2009 than 2010 (Table 4). System productivity index (SPI) decreased from 1981.4 to 1548.4 in 2009 and 1798.1 to 1475.1 in 2010 when strip width increased from 2 to 5 rows. The highest SPI levels of 1981.4 and 1798.1 were obtained for treatment two rows of bean plus two rows of maize in 2009 and 2010, respectively (Table 4). These results demonstrate that productivity in treatment two rows of bean plus two rows of maize treatment was greater than other strip intercropping treatments. The effect of maize compared to bean was more in rising SPI due to higher biological yields. Agegnehu et al. (2006) showed that SPI of barley and faba bean in mixed cropping exceeded those of sole crops. 4. Conclusion These results indicated that intercropping maize with bean improved radiation absorption, RUE and biological yields of both species. The strip width of 2 and 3 rows was superior compared with traits under monoculture and other strip intercropping treatments. Increasing strip width from 2 to 3 rows led to an improved intercropping condition, but with increasing strip width, canopy condition of strip intercropping treatments improved and results were similar to those of monoculture. In all of the measured traits, strip intercropping was more effective for maize than bean. This may be due to the positive effect of bean on maize. LER was greater in all strip intercropping treatments than in monoculture. The crowding coefficient was greater in strip width of 2 and 3 rows compared with others. Moreover, it was higher in maize compared to bean. This demonstrates the predominance of maize on bean. As maize is a C4 plant, it seems that this crop demonstrated greater ability to capture resources leading to its dominance in strip intercropping of maize with bean. System productivity index decreased with increasing strip width. This index was greater in strip width of 2 and 3 rows, but increasing strip widths caused a decrease of this index. Our results revealed that radiation use efficiency and biological yield of maize and bean were higher in 2009 than 2010. This may be due to higher average temperature in 2010 than 2009. The effect of higher temperature in 2010 was more on bean compared to maize. As bean is a C3 plant, it seems that the weather condition of higher temperature affected photorespiration of bean and led to reduction of net assimilation rate and consequently dry matter production. Overall, strip intercropping increased input use efficiency particularly light interception in maize and bean compared with sole crops. Nie et al. (2010) also showed that intercropping maize with

Please cite this article in press as: Nassiri Mahallati, M., et al., Determination of optimal strip width in strip intercropping of maize (Zea mays L.) and bean (Phaseolus vulgaris L.) in Northeast Iran, Journal of Cleaner Production (2014), http://dx.doi.org/10.1016/j.jclepro.2014.10.099

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Please cite this article in press as: Nassiri Mahallati, M., et al., Determination of optimal strip width in strip intercropping of maize (Zea mays L.) and bean (Phaseolus vulgaris L.) in Northeast Iran, Journal of Cleaner Production (2014), http://dx.doi.org/10.1016/j.jclepro.2014.10.099