Study of Indices of Weed Communities in Rice Fields of Guilan Province

The culture of man and rice have historical and profound relationships. Rice (Oryza sativa L.) has an inescapable role in providing food, economy, religion and civilization in many countries of the world. Weeds are among the most important factors affecting crops such as rice. Successful weed control is essential for rice production. Grasses, broad-leaved, sedges, ferns and algae are the weeds of Guilan rice fields. Infestation of weeds in a field can be described by three characteristics of the number of available weed species, the density of each species and the distribution of species in the field. The species in a field are almost constant from year to year, but the other two factors vary greatly in response to the environment, agronomic plans and weed management practices. However, detailed information on the presence, composition, abundance, importance and ranking of weed species depends on weed management strategies with average yield of rice. The objective of this study was to investigate rice weed community richness and composition in the Guilan province, Iran during 2014 and 2016 and their relationships with management. The study was conducted in Guilan province (between 36° 34' to 38° 27' latitudes and 48° 53' to 50° 34' longitudes), northern Iran, with 14044 kilometer square of area. 481 fields were selected from 10 days after transplantation to the end of panicle formation. Taking the area of each field into consideration, 0.25 m2 quadrats were done for sampling using a W-shaped sampling pattern. The weeds at each quadrat were counted and their genera and species were identified. The Frequency, field uniformity over all fields, density of the weeds in each field, the mean weed density of the visited fields, and dominance of the various species in each region were determined. The Simpson index (D) gives more importance to the common species, but the Shannon-Wiener index (H) puts greater importance on rare species. After collecting the data and making the calculations required for determining the population indices, this information created the main layer in the project, and was then designed in the format of a databank. 66 weed species were identified in rice fields of Guilan province, which belonged to 29 families. According to the dominance index of weed, Echinochloa crussgalli was the highest among 66 identified species in Astaneasharafyeh, Amlash, Anzali, Rasht, Roudsar, Siahkal, Fouman, Lahijan and Langroud. Alisma plantago-aquatica had the highest prevalence index in Rezvanshahr. Paspalum distichum was one of the dominant species in shaft, Talesh and Masal regions, having the highest dominance index. Cyperus difformis had the highest dominance index in Somesara. Bolbosoenus maritimus was one of the most important weeds in rice fields located in Roudbar with dominance index equal to 9.9. Azolla filiculoides in 11 regions of Guilan had the highest frequency among floating and submerged weeds in 16 regions. The green algae were the dominant weeds at Astaneasharafyeh and Masal. In the both of regions of Somesara and Lahijan, Lemna minor was the most abundant aquatic weeds. Najas marina is the herbaceous plant having the highest abundance among floating and submerged species in Roudbar. The Shannon-Weiner and Simpson indices were the highest in Talesh (2.85 and 11.93, respectively) and the lowest in Roudbar (1.97 and 3.99, respectively). Uniformity index in Rezvanshahr had the largest quantity equal to 0.806. Identification of weeds is the most important action for weed management. Weed flora composition in rice fields of 16 areas at Guilan Province consisted of 66 species belonging to 29 families. Roudsar and Langaroud regions were the most dominant sites with a total of 47 weed species followed by Rasht and Lahijan (46 sp.), Astaneasharafyeh (42 sp.), Amlash (37 sp.), Talesh (36 sp.), Fouman and Siahkal (34 sp.), Roudbar (32 sp.), Rezvanshahr and Somesara (30 sp.), Masal (28 sp.), Astara (27 sp.) and Shaft and Anzali (25 sp.). Ten species, three grass (narrowleaf) species (E. crussgalli, P. distichum, and E. oryzoides), three sedge species (C. esculentus, C. serotinus, and C. difformis), four broad-leaved species (E. prostrata, S. trifolia and A. plantago-aquatica), and one fern species (A. filiculoides) were the most widespread and of the highest abundance. Frequency, density and dominance of weeds according to the rice ecosystem in different regions can be changed. Due to lack of knowledge on identification and effective weed control factors, the weeds population is growing. Therefore, assessing the management role in changing the weed communities structure of species diversity can be useful to improve weed control.