Study on the effect of agricultural management factors on fungal diseases diversity indices and wheat yield in Gorgan using decision tree analysis CART

To evaluate the qualitative and quantitative effects of agricultural managements on the fungal diseases of wheat, a study was carried out at 67 wheat-grown fields located in 8 villages in four geographical sides of Gorgan, Golestan province, Iran, in 2010. Samples were taken using 0.25×0.25 m quadrates. Then pathogenic fungi were identified and used to calculate the biodiversity of pathogenic fungi, heterogeneity index of Shannon-Wiener and Simpson.Qualitative and quantitative state of agricultural managements was provided by a researcher made questionnaires from farmers. The classification and regression trees (CART) procedure showed that nitrogen fertilizer, plant density and potash fertilizer were the most important management factors affecting the Shannon-Wiener diversity index variations, and nitrogen fertilizer, plant density and phosphorus fertilizer were the most important management factors affecting the Simpson diversity index variations. Moreover, the most variability of wheat yield was mainly interpreted by management factors including seeding rate, nitrogen fertilizer and previous two years rotation. Overall, nitrogen fertilizer and seeding rate (plant density) were common between wheat yield and both Shannon-Wiener and Simpson indices, so that, nitrogen fertilizerexplained 38 and 31% of the Shannon-Wiener and Simpson indices variations, respectively, while 46% of the wheat yield variation was explained by seeding rate. The resultssuggest that appropriate amount of nitrogen fertilizer and desirable plant density were effective management options to improve the yield and reduce the fungal diseases in the Golestan province.