عنوان مقاله [English]
Intercropping is a well-known agro-ecological practice for its dramatic effect on pest and weed control, increasing productivity as well as enhancing resources (radiation, water and nitrogen) use efficiency. All these beneficial effects are the results of increased species diversity which presumably would be higher with introducing more component species. On the other hand, crop growth analysis provides indices for quantifying the rate of dry matter production and allocation of dry matter to the other organs, particularly to leaves. It seems that growth indices of intercropped species relative to their pure stands could be useful for better understanding of higher productivity of more diverse intercrops.
The objective of this study was comparison of growth indices and dry matter allocation as well as land equivalent ratio of fennel (Foeniculum vulgar), common bean (Phaseolus vulgaris) and sesame (Sesamum indicum) grown in monoculture or intercropping systems.
Materials and Methods
The experiment was conducted as randomized complete block design with three replications and seven treatments including pure fennel (F), pure sesame (S), pure bean (B), row intercropping with 1:1 ratio of FB, SB and FS as well as 1:1:1 intercrop of FSB. All treatments were sown in recommended planting date and density. Total aboveground materials of each plot were sampled in 5 randomly selected plants in two-weekly intervals and repeated seven times during growth period. Green leaf area index (GAI) and total aboveground dry matter (DM) were measured for each species in sole and intercropped plots. Time course of LAI and DM was estimated by fitting logistic peak and sigmoid functions to the measured values for each species, respectively. Crop growth rate (CGR; g m-2 d-1) of each species was estimated as the first derivative of the sigmoid function. Economic yield of species was measured by harvesting the whole plots and used for calculation of land equivalent ratio (LER) for intercropping treatments.
Results and Discussion
Results showed that for all studied species, the growth indices were lower in intercropping compared to monoculture. Maximum GAI (1.28), dry matter (184.6 g.m2) and crop growth rate (5.2 g.m-2.day-1) for fennel was observed in pure stand. For sesame, the highest GAI (4.2) was obtained in the sesame – fennel intercrop, however, maximum dry matter (1023 g.m-2) and crop growth rate (24.5 g.m-2.day-1) were achieved in the pure stand of sesame. Similarly in bean, maximum GAI (3.8), dry matter (546.39 g m-2) and crop growth rate were observed in pure stand. However, the lowest GAI (0.61), dry matter (54 g m-2) and crop growth rate (1.6 g m-2 day-1) of fennel was observed in fennel-sesame and fennel-sesame–bean intercrops, respectively. The minimum GAI (3.24), dry matter (286 g.m-2) and crop growth rate (6.6 g.m-2.day-1) of sesame was obtained in fennel- sesame- bean, fennel- sesame and fennel- sesame- bean, respectively. The minimum LAI (3.08), dry matter (110 g.m-2) and crop growth rate (3.26 g m-2day-1) of sesame was observed in fennel- sesame- bean treatment. Despite the lower growth indices, LER was grater that 1 in all intercrops with a highest value (1.09) in sesame – bean showing the better allocation of dry matter between component species of intercropping.
While the LAI, DM and CGR was lower when species were intercropped, the overall rate of dry matter production of intercropping systems was about 28%, on average, higher as compared with pure stands leading to almost 10% higher productivity. Addition of the third species into intercrops has no significant effect on productivity. However, it seems that using species with diverse functional traits to increase functional diversity could cause higher productivity of intercropping systems.