| چکیده انگلیسی مقاله |
Introduction The most significant reduction of the commercial value and quality of leafy crops, such as lettuce, is primarily caused by weeds. The most common weeds in lettuce fields include Lambs quarters (Chenopodium album L.), Redroot pigweed (Amaranthus retroflexus L.), and wild mustard (Sinapis arvensis L.). Although using chemical inputs is considered a successful method in weed control, the risk of accumulating chemical contamination in plants and reducing human health by using these products increased the idea of using safe and environmentally friendly methods. Cover crops are an environmentally friendly strategy for controlling weeds in agricultural fields, offering numerous environmental benefits. Rye (Secale cereale L.) and chickling pea (Lathyrus sativus) are well-known worldwide cover crops. Many studies have mentioned them for their ability to control weeds, improve soil conditions, and release nutrients. Also, hand-weeding is known as one of the simple but expensive weed control methods. In our study, we aimed to explore how rye and chickling pea cover crop residues, when used in monoculture and intercropping systems, can help reduce the need for hand-weeding and improve the yield of Iceberg lettuce, considering the importance of weed control in leafy products. Materials and Methods In the spring of 2020, an experiment was conducted using a factorial design base of RCBD with three replications. The experimental treatments included monoculture and intercropping of rye (Secale cereal L.), and chickling pea (Lathyrus sativus) cover crops, control (without cover crops), and additionally, different levels of hand-weeding were implemented (once, twice, and no hand-weeding). The amount of seed used for the rye and chickling pea monoculture was 100 and 25 kg.ha-1, respectively. For intercropping, 50% of the recommended seed was used. F1 Iceberg lettuce (Bruma Rz.) seeds were planted in a mixture of peat moss and perlite in a 1:5 ratio. Due to the short growing season in Ardabil (20°48' E and 19°38' N), the growth of cover crops was terminated 67 days after the sowing date using paraquat. Then, lettuce seedlings were transplanted manually by 25 × 25 cm inter-row spacing. Hand weeding was conducted at three different stages: once 15 days after transplanting, twice at 15 and 30 days after transplanting, and not at all at the time of lettuce harvest. In this experiment, in addition to investigating the dry weight of cover crops and weeds, weed control efficiency index and fresh yield and lettuce yield components such as number of leaves, plant height, crown diameter, and head diameter were measured. Results and Discussion The results indicated that the highest dry weight of cover crops was obtained from the rye monoculture (530.59 ± 30.15 g.m-2), followed by intercropping (400.21.43 ± 10.37 g.m-2). The lowest dry weight of Chenopodium album L. and Anchusa italica Retz. weeds (0 g.m-2) were recorded in intercropping with one- and two-times hand-weeding. The dry weight of Sinapis arvensis L. in intercropping once, twice, and without hand-weeding, rye and chickling pea monoculture without hand-weeding was 0 g.m-2. The lowest total weed dry weight was found in the intercropping of cover crops with once hand-weeding. The highest weed control efficiency indexes (100, 86.95, and 87.72) were observed with intercropping by once and twice hand-weeding, and chickling pea monoculture without hand-weeding. The highest yield of Iceberg lettuce (3.70 ± 0.82 kg.m2) was achieved by intercropped cover crops without hand-weeding. The maximum number of leaves (21.55 ± 2.69 and 21.44 ± 1.01), crown diameter (4.15 ± 0.13 and 4.18 ± 0.23 cm), and head diameter (20. 22.12 ± 2 and 22.65 ± 2.22 cm, respectively) were obtained from the chickling pea monoculture and intercropping. Conclusion The effectiveness of using cover crop residues for weed control depends largely on the quantity of their dry weight. In the treatments without hand weeding, the rye monoculture and intercropping reduced the dry weight of weeds. The presence of cover crop residues reduced weed growth, although hand-weeding was still a more effective method of weed control in vegetables. However, the results highlighted the impact of cover crop dry weight on reducing hand-weeding for lettuce. In terms of increasing the yield of iceberg lettuce, rye intercropping, and chickling pea were favorable for the Ardabil region's climatic conditions. Acknowledgment The authors would like to express their gratitude to the Department of Plant Production and Genetics, Faculty of Agriculture and Natural Resources at the University of Mohaghegh Ardabili, Iran, for their financial support. |