Quantification of the relationships between grain yield and plant biodiversity with climatic variables and management factors (Case study: canola fields of Gorgan County)

Canola (Brassica napus L.) is one of the most important oilseed plants. It is the third largest sources of oil and meal in the world. While most of the edible oil needed by the country is supplied from abroad, this crop with proper performance and adaptation to different climatic regions can play an important role in increasing oil production and required meal by the country. The potential production of grain yield and oil in canola is affected by environmental conditions and crop management. Therefore, understanding the relationship between plant production and these variables seems to be necessary to achieve sustainable yield. This study was conducted to quantify the relationships between climatic variables and management factors with plant biodiversity and canola grain yield in Gorgan fields.

This study was conducted as a survey in 58 canola fields in Gorgan County, during 2015-2016 crop year. Management data of each field collected by questionnaire and through face- to- face interview with farmers. This data included agricultural history, type of crop rotation, amount of chemical fertilizers and pesticides, type of tillage tools, amount of applied seed, spraying tools, snowing tools and other information about farmers. Also, grain yield of fields was recorded. In continue, the required meteorological information for this study, were prepared from the meteorological office of Golestan Province. The studied climatic variables were annual precipitation, minimum temperature, maximum temperature and average annual temperature. The collected data was then prepared in Excel. In the next step, in order to determine the relationship between yield and plant biodiversity with climatic and management factors, we used the analysis of RDA and Canoco software ver. 4.5.

The results showed that management factors such as farmer's history, fertilizer application, phosphorus fertilizer consumption, cultivar type (Hayola), potassium fertilizer, nitrogen fertilizer, tillage with disc and manure fertilizer application had the important impact on grain yield. Because, these factors had the closer angle with the canola yield vector. But, some factors such as burning the residue of previous crop, manual fertilization, using RGS cultivar, manually sowing and tillage with a moldboard plough had the opposite effect on canola yield. Among the climatic factors, the annual precipitation was the most important climatic factor and affected on grain yield, while other factors such as average, maximum and minimum temperatures had less effects. The biodiversity indices such as Shannon-Wiener, Simpson and reverse Simpson were calculated as 0.9-2.2, 0.11-0.46 and 2.1-4.9, respectively. According to Canoco software output, annual rainfall variable had a positive effect on plant biodiversity indices in canola fields.

In general, based on the results obtained, with the optimal use of nitrogen fertilizer, appropriate pest management, optimal seed consumption, selection of appropriate sowing date, selection of suitable cultivars and seed infection, canola yield can be increased in fields of Gorgan County.