The comparison between adjacent fields in order to evaluate the effect of different managements on soil properties is questionable due to ignoring the soil spatial variability. Our aim was to develop a methodology based on improved space series to differentiate between spatial variability of soil properties and the effect of tillage management in adjacent fields. The study was carried out in a rainfed sloping area consisting two adjacent fields of different tillage direction, i.e. up-down tillage (UDT) and contour tillage (COT). Soil sampling was performed at 80 (40+40) points of 5 m intervals along a straight line at the mid-slope position. All soil properties of UDT were significantly (P<0.05) different from those of COT compared by independent sample T test. But this analysis could not differentiate between the spatial variability of soil and the changes induced by tillage type. We tried to determine the net effect of UDT on soil properties in comparison with COT in the same field. To do this, we (i) performed space series analysis on COT data, (ii) used autoregressive, moving average and autoregressive-moving average models to model the space series data on COT field, and (iii) used the best model obtained for each soil attributes on COT to forecast the value of the property in ten adjacent points in the UDT field. Comparison between the forecasted and measured data in UDT showed that the evaluation of tillage direction effect on soil attributes based on comparison between adjacent fields can be over or under estimated when the sampling coordinates and the spatial correlation among adjacent observations of data are ignored. The methodology used was able to differentiate between natural and management induced differences of soil attributes. Overall, the use of this methodology will improve the prediction and understanding of the effects of different cultivation practices on soil quality.
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