Effects of Intercropping ( Canola-Faba Bean ) on Density and Diversity of Weeds

In order to evaluate the biological effect and interference of crop and weed in canola-faba bean intercropping in comparison with mono culture, an experiment was conducted in randomize completely blocks design with three replication at Ramin Agriculture and Natural Resources, University. In this experiment treatments were different compositions of canola (Brassica napus L. var. haylo) and faba bean (local cultivar). Plant densities (0, 20 and 40 plants per m2) for canola and four levels include (0, 20, 40 and 60 plants per m2) for faba bean in accordance with additive form mixed culture system respectively. Weed dry weight was affected by culture system and different levels of plant densities in mixed culture and there were significant difference 1%. Lowest weed dry weight was obtained in 20-60 and 40-60 plants m-2 canola-bean intercropping. In the intercropping parts only two species was observed while in the sole culture more than three species were exist. Results showed that with increasing in bean diversity, weed dry weight declines. According to our results, it is possible to control weed effectively by using intercropping system, but more studied is required. Diversity of weeds had been clearly affected. Results showed that only Beta and Malva species were existed in intercropping comparing to sole cultures that Brassica, Beta, Rumex and Malva were existed.


Introduction
Intercropping is the agricultural practice of cultivating two or more crops in the same farm and at the same cropping season (Andrews and Kassam, 1976).In intercropping farming system, usually one main crop and one or more were used as added crops (Saka, 2007).The two or more crops used in an intercrop may be from different species or different plant families, they can simply be different varieties or cultivars of the same crop species, such as mixing two kinds of barley seed in the same farm.Main purpose of intercropping is to produce a greater yield on a given piece of land by making use of resources in the way of maximum efficiency.Making attention to the soil, climate, crops, and varieties are very important.Two of intercropping strategies are planting a deep-rooted crop with a shallow-rooted crop, or planting a tall crop with a shorter crop that requires partial shade (Sobkowiez, 2006).Intercropping provides an efficient utilization of environmental resources, decreases the cost of pro duction, provides higher financial stability for farmers, de creases pest damages, inhibits weeds growth more than monocultures, and improves soil fertility through nitrogen in creasing to the system and increase yield and quality (Francis et al., 1976;Willey, 1979).It is now clear that the weeds could interfere with crops by increasing competition (for light, water, nutrients and space) and/or allelopathy.Weeds de-clines many of crops yields and it lead to higher cost in agricultural productions (Wanjari et al., 2001;Pandya, et al., 2005;Singh et al., 2001).There is need to develop the best cropping pattern to increase the production of canola and wheat crop concomitantly.It has been shown that intercropping helps in increasing farm income (Kalra and Gangwar, 1980) while Mandal et al. (1985) reported that intercropping of wheat, mustard and chickpea decreased number of fruiting branches per plant, number of pods per plant and 1000 seed weight.Sharma et al. (1986) reported that plant density showed significant difference by intercropping of wheat and mustard comparing to mono culture.Found that highest land equivalent ratio (LER) was obtained by intercropping wheat and rape in a 1:1 row ratio.Singh and Pal (1994) reported that intercropping of wheat and mustard reduced the seed yield than their pure stands.Whereas, Ayisi et al. (1997) concluded from their experiment on canola-soybean intercropping that seed oil content increased compared with sole cropping.Likewise, Verma et al. (1997) reported that intercropping of wheat and Indian mustard gave maximum net return, benefitcost ratio and land equivalent ratio.One of the most advantages of using herbicides is simplified weed control, but the use of herbicides, not only is costly but also selection of herbicide-resistant weed biotypes seriously become an environmental contamination factor now a day.Herbicide use reduction is one of the main target of sustainable, and dry weights.Intercropping of Triticale and faba bean reduces weed population (Sobkowiz, 2006).
The objective of this study was to evaluate the effects of canola and faba bean intercropping on weed control (density and diversity).

Materials and methods
This experiment was carried out in the research farm of Ramin agriculture and Natural Resources University, located 36 Km northwest Ahwaz in 31 degree and 36 min geographic latitude, in 2004-2005.In this research intercropping of canola ('Hyola 401' cv) and faba bean (local) was investigated.Canola was planted in two 20 and 40 shrubs m -2 densities and faba bean in 0, 20, 40 and 60 shrubs m -2 densities.Experimental design was randomized complete block design, with three replicate.Each plot includes six furrows with 75 cm distance and four meter length, that one cultivation line of each one of two crops is located on those.Treatment was different combination on two crops (canola and faba bean).Treatment of sole culture was used as controls.With the notice of importance of weed status in this research, no chemical nor mechanical weed control procedure were used.Sampling of weeds, in order to evaluate of mixed culture effects on weed status, was done.Weeds were collected at the end of February from the flora and labeled.Diversity and density of weeds in different combination of mixed culture and sole culture were investigated.Then dry weight was analyzed.Agronomic index of Land Equvalent Ration (LER) was calculated using Akter et al. (2004) formula.Data were analyzed using SAS 9.2 and Mstat-C.

Weed dry weight
Analyze of variance shows significant difference of different densities of canola and bean intercropping on weeds dry weight comparing to controls (Tab.1).Lowest weed dry weight was observed on 20 and 40 canola shrubs m -2 and 60 bean shrubs m -2 (5.64, 6.96 gr/m 2 ) respectively.Highest weed dry weight was achieved in sole canola with 20 and 40 shrubs m -2 (Tab.2).Leibman and Dyck (1993), reported that weed dry weight will decrease in intercropping treatments comparing to sole cropping.Morphological and capability of faba bean in competition with other crops showed most reasonable effects on reducing weed  Sole culture of canola exhibited higher weed dry weight and increase in bean densities resulted lower weed dry weight.This was more clear in 20 shrubs m -2 canola, (Fig. 1, 2).
Lower weed density in sole bean culture comparing to sole canola culture, might be because of the higher performance of bean in the competition with weed.
High growth rate, faster canopy closer and covering soil surface for a long time might be good reasons for lower weed densities in the bean parts of the farm.
Role of bean in decreasing weed's dry weight in the canola 20 and 40 shrubs m -2 is different.In the other hand canola density is critical factor for effects of bean on weed dry weight.

Diversity of weed species
Diversity of weed species is varying form sole and intercropping culture (Tab.4).
Weed diversity significanty decreased in intercropping system and it exhibited that farming systems could affected dry weight, diversity and density of weeds in farm.Faba bean has a positive role in controlling weeds of canola and this role is more obvious in lower canola population.Canola seed oil contents affected by different intercropping patterns.Maximum seed oil content (44%) were obtained with canola planted alone and remained statistically on a par with canola + one row of wheat which produced 41.6% seed oil content.However, minimum seed oil content (39.8%) were recorded in a three rows wheat intercropping pattern (Zulfiqar et al., 2000).
Land Equivalent Rate showed different pattern in seed yield in different mixture compositions.Minimum LER (69%) was observed in 40 canola 20 bean (Shrubs m -2 ).LER which calculated in low densities of canola (20 shrubs m -2 ) was lower than 40 canola, in all compositions of mixed culture.It might be the result of effects of increase in number of bean shrubs per unit area and so grain yield of mixture cropping increase and less land was needed to produce grain yield comparing to sole culture.Maximum LER (204%) was obtained in 20 canola shrubs m-1 mixed with 60 bean shrubs m -1 .Mandal et al. (1985) reported that intercropping of wheat, mustard and chickpea could significantly decrease number of fruiting branches per plant, number of pods per plant and 1000 seed weight.Zulfiqar et al. (2000) reported that number of pods per plant in sole canola was higher comparing to intercropping with wheat.Also they reviled that intercropping treatments with two and three rows of wheat exhibited minimum number of pods plant -1 .The decrease in number of pods per plant of canola was result of mutual competition among the two crops for different soil resources.Reduced weed rate of occurrence in canola by intercropping depends on several factors, including species selected to be intercropped (Skóra Neto, 1993), fertilizer doses (Olasantan et al., 1994).Efficacy of cover crops depends widely on soil coverage (> 50%), in fact obstruction of light is the most important effect (Steinmaus et al., 2008).Cover crops could inhibit weed seed germination by a rapid occupation of the open space between the main crop rows, and reducing weed seedling growth and development.Silva et al, 2009 reported that intercropping of corn and cowpea significantly decrease density of weed species, for example, Dactyloctenium aegyptium, Evolvulus ovatus, Herissantia crispa, Passiflora foetida and Waltheria indica.Weed seed germination may be inhibited by two mail reasons, first complete light interception due to cover crop and second existence of allelochemical secretion.After weed seedling establishment, resource competition becomes the cover crop's main weed control mechanism of cover crop (Hollander et al., 2007).

Fig. 1 .Fig. 2 .
Fig. 1.Effects of different faba bean densities in the intercroppingwith 40 shrubs m -2 canola on weed dry weight Tab. 3. Role of canola and faba bean in decreasing weed dry weight