www.ccsenet.org/sar Sustainable Agriculture Research Vol. 1, No. 1; February 2012 Published by Canadian Center of Science and Education 151 Modeling Spray Droplet Size in Order to Environmental Protection Leila Peyman (Corresponding author) Graduated Master of Mechanics Agricultural Machinery, Tabriz university, Iran E-mail: peyman_lb@yahoo.com Shamsollah Abdollahpor Associate Professor of Mechanics Agricultural Machinery, Tabriz university, Iran E-mail: shamstabriz1@yahoo.com Asghar Mahmoudi Assistant Professor of Mechanics Agricultural Machinery, Tabriz university, Iran E-mail: a_mahmoudi@tabrizu.ac.ir Mohammad Moghaddam Professor, Department of Agriculture, Tabriz University, Iran E-mail: moghaddamv@yahoo.com Behzad Ranabonab Graduated Master of Mechanics Agricultural Machinery Head of Design Technology, Tabriz Tractor Manufacturing Company, Iran E-mail: branabonab@gmail.com Received: November 10, 2011 Accepted: January 19, 2011 Published: February 1, 2012 doi:10.5539/sar.v1n1p151 URL: http://dx.doi.org/10.5539/sar.v1n1p151 Abstract Million liters of annual toxic solutions are used to combat pests and plant diseases and weeds in farms. Drift is one of the most critical problems which chemical applicators have to deal with. Wind drift would be highly controlled if the droplet size could be kept almost constant in stable atmospheric conditions.The most important factor in spraying is droplet size which is influenced by several factors including; spraying pressure, nozzle orifice diameter, the chemical viscosity and wind speed in the region. In this study factors affecting particle size have been studied using statistical methods. Nozzle orifice diameter and spraying pressure were considered as independent variables and particle size was chosen as the dependent variable. Analysis of variance showed that the effect of pressure and nozzle diameter and their interactive effect on particle volume mean diameter (VMD) were statistically significant at the 1% level. In order to compare the results estimated from regression equations and observed particle diameter chi-square test was used. Based on this test, the difference was not significant . Keywords: Maintaining, Particle size, Pressure, Spraying 1. Introduction Each year about 25 to 35 percent of total world agricultural crops be devastated by insects, weeds and plant pathogenic. This amounts increase to 80 percent in non-combat status(Mansourirad, 2005). Drift (toxin movement by air currents) of the distributed place may lead to contamination of nearby crops that are grown for human consumption or animal. Droplet size and distribution of pesticides are the main factors that will determine the treatment efficiency. Liquid pesticides may be contact or absorption type. With Contact pesticides, pets are disappeared. To have full effect this material is better to be distributed as fine particles at all levels. Absorbed