Mapping the Distribution and Flora of the Weeds in Canola Fields of Gorgan Township by Geographic Information System (GIS)

Oil seeds are the second world’s food supply after cereals. These crops are grown primarily for the oil contained in the seeds. The major world sources of edible seed oils are soybeans, sunflowers, canola, cotton and peanuts. Canola is one of the most important plants in the world that has great importance. The plant belongs to the Brassica genus, the botanical family that includes cauliflower and cabbages. Weeds are one of the major problems in canola production that reduce yield and its quality. In general, one of the most important factors in development of management plans is information about the weed’s flora and geographic distribution. Knowledge of weed flora enables one to use the required herbicide and formulate other suitable management strategies. It is also useful in exploiting abundant weeds as a cover crop or pasture and for other economic uses. The geographic information system has the proper use in weed science and management of agricultural information and their analysis. In this study, distribution and flora of the weeds in canola fields of Gorgan Township investigated by Geographic Information System.
Material and Crop sampling was conducted during May and June 2014, in 58 canola fields in Gorgan Township (Golestan province) and the weed species were sampled and detected using a W method and by specific formula of density, frequency, uniformity, and abundance of each weed species was calculated. Also, geographic coordinates of fields (latitude, altitude and elevation) were determined by using GPS model Garmin map 60. After collecting data, in order to create a database of weed distribution, the data was transferred from GPS to ArcGIS 9/3.1 software. From all information obtained, consistently a database with location was created and after separation of data based on present or absence of weeds on fields, distribution maps were produced.
The results showed that there are 35 weed species in canola fields of Gorgan Township and these belonged to 18 families. About 17.1 percent of these species belong to Poaceae and 11.4 percent belongs to Asteraceae and other families, respectively. In general, 77.2 and 22.8 percent of species were annual and perennial weeds, respectively. Also, 80 percent of weeds belong to dicotyledonous and 20 percent to monocotyledonous. The most important species of Poaceae family were Phalaris minor, Avena ludoviciana, Alopecuros sp., Poa annua, Lolium temulentum and Bromus sp. Also, the most important species of Asteraceae were Artemisia annua, Cirsium arvense, Sonchus sp. and Senecio vulgaris. 85.7 percent of weeds reported as broad-leaved weeds and 14.3 percent belong to the narrow leaves. Phalaris minor was the most important weed of narrow leaves and Melilotus officinalis was the most important broad leaf out groups. Among the weeds have been identified, 88.5 percent had photosynthetic cycle of C3 and 11.5 percent were C4. The study results also showed that Phalaris minor had the highest relative dominance among the 35 species and then Melilotus officinalis, Rapistrum rugosum and Avena ludoviciana had 29.4, 28.9 and 23.5 of relative dominance, respectively. To view maps of distribution, based on the abundance of weeds, the three categories 50-100 percent, 30-50 percent and lower than 30 percent were classified. Weeds that have had 50-100 percent frequency were considered as the most important weeds in canola fields of Gorgan. These weeds includes: Phalaris minor and Melilotus officinalis. Weeds that have a frequency between 30-50 percent were considered as medium importance weeds that included Sinapis arvensis, Veronica persica, Avena ludoviciana and Rapistrum rugosum. In final, the weeds with a frequency of less than 30 percent, were placed in the third group as small percentage of surveyed fields. The most important weeds in this group recorded as Artemisia annua, Ranunculus sp., Polygonum convolvulus and Alopecuros sp.
In general, weed distribution maps showed that Phalaris minor, Melilotus officinalis, Rapistrum rugosum, Avena ludoviciana, Veronica persica and Sinapis arvensis are present in the most of canola fields in Gorgan region. Therefore, we can be conclude that, observation of high diversity and high dominance of weeds in these fields, may because of similar cropping management by farmers. So, it is recommended as a first step to produce the weed and seed banks maps. On the other hand, we should institutionalize strategies based on sustainable management of weeds.