عنوان مقاله [English]
Introduction: Maize (Zea mays. L.) is an important food and feed crop of the world. Maize is the third most important cereal crop of Iran after wheat and rice. About 60% maize is grown in irrigated and 36% in rain fed areas of Iran and other country of Asia. Basically it is a tropical plant but at present it is being cultivated extensively with equal success in temperate, tropical and sub tropical regions of world. Crop density is one of the usage tools in sustainable agriculture at integrated weed management. Also weed species response varie according to density of species in agricultural ecosystems. The purposes of this study were to investigate cooperation of species (weeds and crop) was applied in the field at five stages to determinate (1) evaluation some physiological indices of plant species in different levels of irrigation (2) changes of total dry matter of species in different levels of irrigation in field conditions and (3) survey affect of different levels of irrigation on growth indices of species in corn field.
Material and Methods: Because of the importance of plant species can absorb water, irrigation water and soil and water quality and maintain their role in the determination of competition within and between plants a field experiment was conducted based on interval mapping at the Agronomy Research Field of Ferdowsi University of Mashhad, Iran (Lat 36°15' N, Long 59°28' E; 985 m Altitude) during 2009. Treatments consisted of four levels of irrigation (610, 730, 880 and 1230 mm) and two levels of weed control (complete control and without control). Weed sampling was done at 5 stages including first, middle and end of critical period weed control and at Maturity and 2 weeks after that then all weed species counted, species identified, leaf area and dry matters of samples were measured. Total Dry Matter calculated from integral of Crop Growth Rate (g.m2.day-1) in period of growth. TDM= a/1+b * (exp (-c * t)) and CGR= (a* b * c * (exp (-c * t))) / (1+ b * (exp (-c * t))) ^ 2. That a is TDM of point in asymptote of curve, b is rate of achieve to asymptote, c is crop growth rate, t is time.
Results: The results showed that in different levels of irrigation the weed species were different. The coefficients of inter and intra species competition for corn and weeds had high correlation with level of irrigation. At all species, the highest and lowest coefficient of intra species competition, respectively, related to the nightshade (3/66) in irrigation and Common lambsquarters 1230 mm (408/0) in irrigation was 730 mm.
By increasing the amount of irrigation water rates increased in proportion to the amount of dry matter production of maize. In the treatment of uncontrolled weed dry matter production of maize compared to the control (weed control) showed a 29% reduction in the maximum amount of irrigation water has had all the species with the highest amount of dry matter production. The highest growth rate in the treated corn irrigation lowest, compared to other treatments (47/53 g / m2 / day), and the average amount of irrigation water, growth rate (80/19 g / m2 / day) had the lowest. In general, application of high levels of irrigation is suitable for crops at absence of other species. In conclusion, increasing the irrigation at complete control to a certain extent, leading to increased production and more than that would not.
Conclusions: According to the results, increasing of irrigation at complete control reduced coefficient of intra species competition corn. Increasing relative density of corn leads to negative coefficient of intra species competition on the dry matter. So increasing density of corn is positive factor at presence of other species and availability of irrigation. High density of species, tend to highest (nightshade at irrigation treatment of 1230 mm) and low density of species tend to lowest (Common lambsquarters at irrigation treatment of 730 mm) coefficient of intra species competition respectively among weeds. Also increasing irrigation leads to increasing dry matter of corn. Maximum of corn CGR was in irrigation treatment of 630 mm. We concluded that in this experiment, effects of different levels of irrigation on Physiological Indices consist of TDM of weeds and crop, CGR of species was studied in different controls of weeds.