مجله کشاورزی بوم شناختی
سال چهارم شماره 1 (1393)

The vertical distribution of leaf area and dry matter is considered to be an impact factor on light absorption, evapotranspiration of canopy, dry matter accumulation and seed yield. To study the vertical distribution of leaf area and dry matter of the maize canopy in competition with weeds and cover crops, an experiment was conducted at Sari in 2011. This experiment was performed in a randomized complete block design with 8 treatments and three replications. Three cover crops, namely bean (Phaseolus vulgaris), soybean (Glycine max L.) and berseem clover (Trifolium alexandrium), were planted on two dates: simultaneous with and 21 days after maize sowing (delayed planting). In addition, maize sole crop with weed control and weed interference was added to the treatments. The results showed that dry matter and leaf area index of bean and soybean were higher than for clover. The delayed planting of bean and soybean increased the leaf area index of maize upper layer canopy rather than sole cropping of maize with weed interference: this approach caused an increase in the competitive ability of maize against weeds. The leaf area and dry matter of weeds were reduced more by bean and soybean than by berseem clover. The cover crops caused the maximum amount of weed (in particular, veveltleaf and bermuda grass) dry matter to be accumulated in the primary layer. The cover crops reduced the number of layers and dry matter of per layers in the weed canopy. For maize, the dry matter was less in the presence of berseem clover than for the two other cover crops. The maximum amount of weed dry matter was accumulated in the primary layer. Grain yield in maize was higher in simultaneous sowing than in delayed planting of cover crops, especially soybean. The cover crops’ dry matter had a positive correlation with dry matter of maize and was negatively correlated with dry matter of weeds. The yield of maize in the present of crop cover was higher than for sole cropping of maize under weed interference. The grain yield of maize with a delayed presence of cover crop was higher than at the same sowing date.

Irrigation systems have various impacts on agriculture in terms of their ecological, social and economic aspects. Understanding these effects may contribute to develop appropriate policies and strategies for sustainable agriculture. Accordingly, the present research was conducted to determine the impacts of irrigation systems development on agriculture in Tehran. A survey was undertaken with a sample of 72 experts and specialists of irrigation systems development selected using the Snowball technique as a non-probability sampling. The main research tool was a questionnaire the validity of which was reviewed by members of the expert group. Reliability of the questionnaire was obtained at 0.85. The results revealed that sustainable resource management, employee and income, environmental impacts, intuitional trust and development, mechanization, productivity, improvement of quality of life, expansion of land fields and improvement of population profile are all key impacts of irrigation systems development on Iranian agriculture. These factors could measure about 73.142 per cent of total variance.