Preparation of Water Requirement Maps of Maize by Comparing Geostatistical and Deterministic Methods

Preparation of maize water requirement maps in Mazandaran province was considered in the current study. The 10-day maize water requirement firstly was computed in the weather stations postitions using the FAO 2- stage approach. Reference evapotranspiration (ET0) was computed by FAO modified Penman-Monteith method and climate data from 51 weather stations. Crop coefficients were considered in 4 satages during growing season. To evaluate the spatial structure of the data, Trend and Aanisotropy in the data were analyzed. After computing experimental semivariances and selecting the best semivariogram model on the basis of the lower Residuals Sums of Squares (RSS), data were interpolated by deterministic (Inverse Distance Weighting, Global Polynomial Interpolator and Local Polynomial Interpolator) and geostatistical (Ordinary Kriging and Universal Kriging) methods. The interpolation accuracy was compared based on cross validation technique and showed that Global Polynomial Interpolator and Ordinary Kriging had the same results and were better than the other methods. Maps showed that the highest amount of ET0 occurs in August (Mordad) and 4.05 to 4.78 mm/day and the lowest amount occurs in January (Dey) and 1.05 to 1.27 mm/day. Also, the highest amount of silage maize water requirement occurs in third decade of June and two first decade of July (Tir) and 4.27 to 5.15 mm/day. The highest value of maize water requirement occurs in third decade of July (Mordad) and 4.41 to 5.21 mm/day, too. The computed and predicted silage maize water requirement for Dasht-e-naz station in the current study is lower 45.8 and 45 percent than the Reference Book results. Also, the computed and predicted maize water requirement for Dasht-e-naz station in the current study is higher 71.9 and 75 percent than the National Water Document results.