مطالعه جنبه‌های زراعی و بوم‌شناختی نظام‌های کشت مخلوط افزایشی و جایگزینی ذرت (Zea mays L.) و سویا ( Glycine max L. Merr.)

Introduction
Intercropping is a multiple cropping agricultural practice involves growing two or more crops in close proximity. Intercropping of compatible plants also encourages biodiversity, by providing a habitat for a variety of insects and soil organisms that would not be present in a monocrop environment. This in turn can help limit outbreaks of crop pests by increasing predator biodiversity. Additionally, reducing the homogeneity of crops increases the barriers against biological dispersal of pests through the crops. Cereal–legume intercropping plays an important role in subsistence food production in developing countries, especially in the situations of limited resources. Nitrogen fixing legumes can be included to a greater extent in arable cropping systems via intercrops. Legumes contribute to maintaining the soil fertility via nitrogen fixation, which is increased in intercrops due to the more competitive character of the cereal for soil inorganic N. Ariel et al., (2013) showed that,Legume-Cereal Intercropping of corn and soybean may be advantageous compared to monocultures. Corn and soybean intercropping produce high yields of green matter and seed concentrates especially when the corn-soybean ratio is 1:2.
Due to the importance of cereal–legume intercropping in the sustainability of agricultural systems, the objective of this study was to determine the effects of cereal-legume intercropping on the total biomass and grain yield and to find the best pattern of additive and replacement intercropping systems in Iranshahr Region.

Material and Methods
In order to study the agronomical and ecological parameters of additive and replacement intercropping systems of corn and soybean, a field experiment was conducted in 2012-13 in the south of Iranshahr city on a randomized complete block design with three replications. Treatments consisted of 8 different intercropping ratios: corn monoculture (C100S0) and soybean monoculture (C0S100) as sole cropping; 75% corn + 25% soybean (C75S25), 50% corn + 50% soybean (C50S50), 25% corn + 75% soybean (C25S75) as replacement intercropping; and 100% corn + 50% soybean (C100S50), 50% corn + 100% soybean (C50S100), and 100% corn + 100% soybean (C100S100) as additive intercropping. Seed yield, biological yield, harvest index (HI), relative yield total (RYT), leaf area index (LAI), Photosynthetic active radiation (PAR) were measured for both species in this experiment. All data were statistically analyzed using analysis of variance (ANOVA) using MSTATC statistical software. The Duncan’s multiple ranged test used to compare means at 5% probability level.

Results and Discussion
The results showed that the highest seed and biological yield of corn and soybean were obtained from sole cropping of both species. The RYT of seed and biological yield for most intercropping ratios were greater than one which indicates the advantageous of intercropping over sole cropping. This was observable that among intercropping treatments, additive intercropping was better than replacement intercropping for mentioned indices. Comparing the performance of sole cropping and intercropping treatments, the results indicated that weed suppressing effects was more effective in additive intercropping treatments. The highest PAR interception also obtained in additive intercropping treatments. The highest amount of harvest index and leaf area index was obtained from intercropping and sole cropping, for corn and soybean respectively. Generally in this research, Intercropping treatments had a better performance than sole cropping, because of more efficient use of sources (such as light and nutrients) and also preventing weed’s growth.

Conclusion
According to the results of the present research, intercropping systems were more efficient than sole croping in RYT (seed and biological yield), LAI, PAR, harvest index (only for corn) and weed suppressing indices. Among intercropping treatments, additive intercropping was better than replacement intercropping for mentioned indices. Generally, the results of this experiment showed that in order to obtain optimum yield of two species and effective management of weeds, this is better to use additive intercropping system rather than other cropping systems in this region, especially for smallholder farmers use less machinery in their farms.