واکنشهای نامتقارن و مداوم در نوسانات قیمت کود از طریق دوره های پایدار و ناپایدار

Fertilizers are important to improve agricultural productivity growth. The purpose of this study is to investigate asymmetry, leverage, and persistence of shocks on price volatility of five fertilizers using EGARCH model during stable and unstable time periods, corresponding to before and after 2007 international financial crisis, respectively. Using price data of rock phosphate, triple super phosphate, diammonium phosphate (DAP), urea, and potassium chloride, it is found that fertilizers price volatilities display an apparent asymmetric response to shocks which have much pronounced and permanent effect during unstable period than in during stable period. Such effects should be taken into account whenever volatility modeling of fertilizers is considered, particularly during periods of volatile price.