Comparative Analysis of Soybean (Glycine max L.) Weed Flora in Mountain and Plain Regions in the East of Mazandaran Province

Weed distribution studies are useful not only for increasing in herbicide application efficiency but also for evaluating and designing the agronomical approaches and weed management strategies. Community assembly theory provides a useful framework to assess the response of weed communities to agricultural management systems and to improve the predictive power of weed scientists. Under this framework, weed community assembly is constrained by abiotic and biotic ‘‘filters’’ that act on species traits to determine community composition. Weed management practices vary between conventionally and organically managed systems. The main filter in conventional systems likely would be herbicides, which are strong filters that select tolerant species against susceptible species. , Other filters like fertilizers also represent potential filters on weed community assembly. Therefore, this experiment performed in order to determine species and functional diversity and weed community structure in the soybean fields in two plain and mountain regions, which located in Neka and Galugah counties in the east of Mazandaran province.

In order to arrange the experiment, two Neka and Galugah counties were selected in the east of Mazandaran province. In Neka, all the experimental fields were in the plain but in Galugah some fields located in the plain and some in the mountain regions. According to the potential of selected field, sampling were done in five to nine points in each field. The total area sampled was 2820 ha and systematic sampling method was done at the stage of fourth growing nude (V4) in 2018. The size of quadrates was 0.5×0.5 m. For each species recorded in the quadrates, density, frequency and their evenness were measured. Shannon index was used to estimate of diversity. Sampled plants categorized on the four functional groups; life cycle, morph type, photosynthesis pathway and insistence degree. In some collections belongs to multivariate data, variables naturally divided in two groups. In this situation canonical correlation analysis (CCA) be used for determination relationships between them.

Overall, 47 weed species from 23 families were recognized. Asteraceae and Poaceae families each with eight species had the most species richness. The frequency of annual and perennial weed species were 33 and 13 plants, respectively. In mountain fields, broadleaf weed species was more because herbicide was not used. Because benefiting of low temperature in mountain fields, C3 plants had more share relative to C4 ones. Shannon index in the mountain region (Hm=1.13) was estimated more than the plain region (Hp=1.04), this subject related to further sustainability. Less weed density in the plain fields it seems arise from role of cultivation. The plain region had low species richness because agronomical managements possess intensive effects on the weed frequency and diversity. In this place, herbicides were the most important agents. The studies often have shown that perennial weeds are more in the fields in which they are applied minimum tillage or exist in cold places. This subject is caused from preservation food resources in the reserves organs. Johnson grass had more density in the plain relative to mountain regions, which its reason related to segment their rhizomes. Many species correlated with Min tillage have seeds which spread with wind. For example, Dandelion, Grinning swallow and Prickly lettuce observed only in the mountain. Using crop cultivars with high compatibility has a special role in reduction yield loss. So that characteristics such leaf area and plant height have straight link with competition ability. In this study cultivars such as 033 and JK were used (full leaf and tall). From 12 species that only observed in the plain, barnyard grass, goose grass, ground cherries, garden purslane and common heliotrope completely adapted to the warm and humidity conditions that existed in this region. Using CCA to analysis the relationship of site and functional groups confirmed that the majority species in the mountain regions were dicotyledonous, C3 and annual species.

Our conceptual framework proposes showed that weed community assembly in the soybean fields affected by a series of filters, such as herbicide, tillage, cultivars, fertilizer and temperature. Generally, different management in two regions for a long time as agronomy filters affected weed density and their composition. Our results suggest that the effects of crop management factors are more important than the environmental factors on soybean weed composition in a county-wide context even for intensified agriculture.