بررسی رقابت و عملکرد کمی و کیفی در کشت مخلوط سویا (Glycine max (L.) Merrill.) و همیشه بهار (Calendula officinalis L.)

Introduction
With the continuous growth of world population, degradation and ecological imbalance throughout the world, there is a need to increase agricultural production and environmental protection measures. In this respect, efforts to supply nutrients to the environment are at the head of the programs. One of the ways to approach this goal is the use of intercropping systems (Najafi & Mohammadi, 2005(. Suitable performance in intercropping systems may be achieved by selecting genotypes possessing traits consistent with and appropriate for establishing minimum and maximum synergy and competition employing proper agronomic practices such as density and planting pattern (Mutungamiri et al., 2001). In this context, selected plants should be less competitive in terms of environmental impact. The purpose of this study was to investigate the effect of different planting patterns on the competition between the two species of Calendula and soybean and to evaluate the yield and quality of an intercropping system compared with a mono-cropping system.

Materials and Methods
In order to evaluate the competition between soybean and calendula, a field experiment was conducted based on randomized complete block design with 7 treatments and 3 replications in the research farm of the Faculty of Agriculture, the University of Tabriz in 2009. The treatments included pure stands for both species, 1:1, 2:2, 4:2, 4:4 and 6:4 for soybean and calendula number of rows per strip, respectively. Before planting, soybean seeds were inoculated with Bradyrhyzobium japonicum. Before harvesting, the number of pods per plant, seeds per plant, 1000- grain weight, grain yield, percentage of oil and protein of soybean grain were measured in 10 randomly selected plants. The number of flowers per plant, dry inflorescence weight and dry petal weight of Calendula were recorded. The harvest of flowers of calendula began on July 30 and harvesting was done every 15 days in six steps. It was continued to mid-October. Total dry petals and sepals of 6 withdrawals flower per plot were considered as inflorescence dry weight. The land equivalent ratio (LER), actual yield loss (AYL), relative crowding coefficient (RCC), aggressivity (A) and competitive ratio (CR) were determined at the end of the growing season. For statistical analysis, analysis of variance (ANOVA) and Duncan’s multiple range test (DMRT) were performed using MSTAT-C.

Results and Discussion
The results showed that the effect of planting pattern on the number of pods per plant, seeds per plant, 1000-grain weight, grain yield of soybean, percentage of oil and protein contents of soybean was not significant. The effect of planting pattern on inflorescence dry weight and dry petal weight of calendula was significant. Row and strip intercropping 6:4 produced greater dry inflorescence weight and dry petal weight than calendula monoculture. The highest petal and inflorescence yield was achieved by 1:1 (87.63, 30.75) and 6:4 (41.75, 22.68) intercrops, respectively. The effect of planting pattern on the number of flowers per plant was significant at 1% level. The number of flowers per plant for row intercropping and strip intercropping of 1:1 and 6:4 were greater than calendula monoculture. The highest flowers per plant was achieved by 1:1 and 6:4 intercrops, respectively. The land equivalent ratio was greatest for 6:4 and 1:1 intercrops equal 1.34 and 1.13, respectively and the lowest land equivalent ratio was achieved by 2:2 intercrops. The actual yield loss value of all treatments were positive that indicated increased yield. In row intercropping and strip intercropping 4:4 and 2:2 competitive ratio of calendula (1.13, 1.25, 2.06) was>0 and the competitive ratio of soybean (1.07, 1.2) was>1 that show that yield advantage was greater than mono-cropping system. The relative crowding coefficient (RCC) of calendula (0.46, 0.46, 0.76) was greater than that of soybean that proves the competitive advantage of calendula against soybean. In strip intercropping, 6:4 and 4:2 aggressivity of soybean (0.98, 1.43) was>0, that indicates the relative yield of soybean is greater than calendula. The negative aggressivity of calendula (0.93, 1.19) in this treatment shows that the relative yield of calendula is less than soybean. In row intercropping and strip intercropping 4:4 and 2:2 competitive ratio of calendula (1.13, 1.25, 2.06) was>0 and competitive ratio of soybean (1.07, 1.2) was >1 that shows that yield advantage was greater than mono-cropping system.