Onion (Allium cepa L.) seed yield improvement by intercropping with ajwain (Carum copticum Heirn) and chamomile (Matricaria chamomilla L.)

The cultivation of medicinal and aromatic plants has a special status in Iranian traditional agricultural system due to the different weather conditions and the history of the use of medicinal herbs. These systems play an important role in creating diversity and stability. In this regard, this study was carried out to investigate the effect of ajwain and chamomile as two insect attractive plants on improvement the yield of onion seed production under intercropping systems. The experiment was conducted on a field located in 10 kilometers west of Shirvan, North Khorasan province, Iran.

The experiment was conducted in a randomized complete block design with ten treatments in three replications. Treatments were including of sole sowing of ajwain, one row intercropping of onion and ajwain, two row intercropping of onion and ajwain, three row intercropping of onion and ajwain, sole sowing of chamomile, one row intercropping of onion and chamomile, two row intercropping of onion and chamomile, three row intercropping of onion and chamomile, sole sowing of onion by free pollination and sole sowing of onion under cage. The measured criteria for onions were plant height, number of umbrellas per square meter, number of fertilized capsules in umbrella, number of infertile capsules, number of seeds per capsule, number of flowering stems, 1000 seed weight, seed yield per hectare and harvest index. The onion seeds were harvested manually. Characteristics such as plant height, 1000 seed weight, seed yield per hectare, biological yield and harvest index were recorded for ajwain, and for chamomile, traits such as plant height, dry inflorescence yield per hectare, biological yield per hectare and harvest index were measured

The results showed that the maximum number of inflorescence 32.46 per m2), seed yield of onion 462kg/ha) and biological yield 9973 kg/ha) were obtained in sole sowing of onion by free pollination and the maximum harvest index for seed 7.001) and bulb 95.31) were observed in sole sowing of onion by self-pollination. However, the maximum number of fertile capsules in onion inflorescence was obtained in three row intercropping of onion with ajwain and chamomile 151.57 and 154.36, respectively) and thousand seed weight of onion 4.82 g) was observed in three row intercropping of onion and chamomile. The highest thousand seed weight of ajwain 1.33 g) was obtained from three row intercropping by onion while the highest seed yield 2001 kg/ha) and biological yield 2915 kg/ha) were obtained in sole sowing of ajwain. We observed the highest chamomile dry weight of plant, dry flower and harvest index 358.6, 164 and 45.84, respectively) in sole sowing and then in three row intercropping by onion. The maximum amount of LER was obtained in three row intercropping of onion by ajwain and chamomile 1.16 and 1.15, respectively) that it shows this pattern of intercropping superiority to sole sowing.

According to the results, it can be concluded that the combination of three rows of onions with chamomile and ajwain, having the proper density of each plant, provides better use of plants from environmental resources and improves the attraction of insects, improves pollination of onions flower and increase the yield of all three plants.