اثر روش‌های مدیریت غیرشیمیایی بر جمعیت و تنوع علف‌های هرز در مزرعه اسفناج (Spinacia oleraceae L.)

Introduction
Weeds are often recognized as the most serious threat to crop production especially vegetables. Competition from weeds is the most important factor that decline agricultural crop yield. Spinach is one of the most important summer vegetables. It has an extremely high nutritional value and is rich in antioxidants. This vegetable is also an excellent source of vitamin K, vitamin A, vitamin C and folic acid as well as being a good source of manganese, magnesium, iron and vitamin B2.
The reduction in yield of some vegetables caused by the uncontrolled growth of weeds estimated 49% in cauliflower, 80% in okra and 91% in onion. Enhancing application of chemical herbicides to manage agricultural weeds is in a primary concern today. Widespread herbicide application use during the last few decades has caused serious ecological, environmental and biological hazards such as crop loss, decreasing biodiversity, reducing food quality, weed dominance and weed resistance. Therefore, all those operations of weeds which can prevent germination and surpass growth of weeds and improve crop competitiveness must be integrated to control weeds.
The objectives of this study were to evaluate different weed management methods on population, density, dry weight and Shannon-Weiner diversity index for weeds in spinach field.
Material and Methods
An experiment was performed based on a randomized complete block design with three replications at the Agricultural Research Station, Ferdowsi University of Mashhad during growing season of 2012-2013. Treatments were solarization with dark and transparent sheets, crop residues of sunflower, barley and garlic, hand weeding and control (without weeding). Polyethylene sheets were placed on the soil surface after irrigation based on field capacity at two months before planting time of spinach. After land operation, 5000 kg ha-1 crop residues of each species were added to the soil. Hand weeding was carried out at the end of fall and winter before canopy closure. Weed samplings were done at three stages including planting time, 19th February and before harvest stage. Relative density, density, dry weight and Shannon-Weiner diversity of weeds were measured and calculated.
The treatments were run as an analysis of variance (ANOVA) to determine if significant differences existed among treatments means. Multiple comparison tests were conducted for significant effects using the LSD test.

Results and Discussion
The weeds flora infesting the spinach field were abyssinian finger grass, alyssum, barnyard grass, black nightshade, blackgrass, Canada thistle, charlock, common amaranth, common chickweed, common knotgrass, common lambsquarters, common purslane, corn flower, delphinium, field bindweed, field milk-thistle, flixweed, fumitory, Hoary cress, nut grass, prostrate amaranth, Russian knapweed, shepherd's-purse and Syrian mustard that Brassicaceae was the most dominant family. The lowest weed number was obtained for dark polyethylene with two species at the first, second and third samplings. The effect of non-chemical weed management methods were significant (p≤0.01) on weed density, dry weight and Shannon-Weiner diversity index at three sampling stages. The lowest weed density for the first, second and third stages were achieved in dark polyethylene (with 8.3, 5.6 and 16.7 species m-2, respectively) and the highest was for control (with 94.4, 63.9 and 116.7 species m-2, respectively. Although crop residues reduced weed density and dry weight for total sampling stages but, the highest decrease was for barley residues. The maximum Shannon- Weiner diversity for weeds for the first, second and third samplings were calculated in control with 0.81, 0.76 and 0.7 and the minimum was for dark polyethylene.
Conclusion
Non-chemical weed management strategies had significant effect on density, dry weight and biodiversity indices of weeds in spinach. Soil solarization with dark and transparent sheets, Cover crops and crop residues provided economic control of soil-borne pests and weeds, enhanced the physical and chemical properties of the soil, increased the yield of spinach and is cost-effective. Generally, soil solarization is a safe and effective technique for weed control that may decrease the necessity for chemical approaches to crop and soil.
Acknowledgement
This research (23340.2) was funded by Vice Chancellor for Research of Ferdowsi University of Mashhad, which is hereby acknowledged.