Evaluation effect of density and weeds control in corn (Zea mays L) and peanut (Arachis hypogaea L) intercropping by competition indices

Evaluating yield in intercropping systems is based on selecting compatible plants with appropriate characteristics to establish minimum competition and maximum cooperation, and the application of suitable agricultural practices (crop density and intercropping ratio). The use of plant species with different morphological characteristics in terms of nutrient uptake and utilization of growth environment, and the least competitive species in ecological and environmental factors in a fixed nest causes possibility of presence of two plants in the same ecological niche and better use of resources (Banik et al, 2006; Mushagalusa et al., 2008). Competitive ability of species in the intercropping is estimated using the relative interference parameters and determining the dominant species (Dhima et al., 2007). One of the indicators to evaluate intercropping is competitive ratio which is the competitive ability of the crop in the form of a better expression (Dhima et al., 2007). In general, the intercropping is one of the ways that increases the stability of agroecosystems.
In order to study the effects of density, weedy and various proportion of corn (704 Variety) and peanut (Goli Variety) intercropping an experiment was conducted in 2012 in the Agriculture Research Station (Chah Nimeh) of Zabol University. The experiment design was factorial in randomized complete block design with three replications. Experiment factors consisted of planting proportions in 4 levels (sole crop of corn, 50% corn % peanut, 100% corn 100% peanut and sole crop of peanut), weedy in 3 levels (non-weedy, once-weedy and twice-weedy) and the space between rows in 2 levels (40 and 50 centimeter). For appointment of dominant treatment, Relative Crowding Coefficient (RCC), Competitive Ratio (RC), Aggressivity and Land equivalent ratio (LER) were calculated. All treatments were planted in a row of peanut and a row of corn. In intercropping alternative treatments and increasing sowing ratio with bush density change (the distance change between two bushes on a row) and variable distance between two rows (40 and 50 cm) were carried out. In monoculture and alternative intercropping systems, the distance between bushes for both plants was identical, but alternative intercropping, a row of corn and a row peanut were planted and there were 30 plants of corn and 40 plants of peanut per unit area on each row. To intensify the intercropping, the distance between plants on the rows decreased and due to variable spacing between rows, number of plants per unit area increased and there were 60 corn plants and 80 peanuts plants per unit area on each row.
The highest yield for corn (3.18 t.ha-1) was obtained in a intercropping of 100% corn흍% peanut and peanut (9.43 t.ha-1) in 50% corn% intercropping of peanut respectively. This means that the proximity of the legumes and grasses can be more productive in terms of intercropping than mono cropping system. The reason could be due to biological nitrogen fixation and increases in light absorption by roots of peanuts. Results indicated that various factors had significant effects on valuated index. The highest and least LER was in 100% corn 100% peanut and 50% corn 50% peanut. The highest RCC was for peanut, treatment non-weedy at higher population (7.41) and least was in the corn, treatment once-weedy at lower population (0.4). Corn competitive ratio on peanut in all treatments was less than one, which indicated peanut had advantage over corn. Based on this scale treatment with less density and twice-weedy was more dominate. The Aggressivity index for corn in all the treatments were negative but increased. Therefore in the all indices peanut was the dominant species, this was referred to better use of resources and weed control.
The results showed that both morphology and structure of the components of a intercropping, in dominant and recessive forms are effective. Row spacing and weed control are factors affecting the competitiveness and profitability indicators in intercropping. Peanut was the dominant species and a top competitor in corn and peanut intercropping with higher Aggressivity index, relative interference and higher competition and to the effective use of environmental resources and weed control, which makes it the most serious rival for corn.