Implications of Spatial Variability of Soil Physical Attributes in Delineating Site-Specific Irrigation Management Zones for Rice Crop

The primary objective of this study was to investigate the spatial variability of soil physical attributes and subsequently delineate site-specific management zones for irrigated rice cultivation in Guilan province, Iran. By achieving this objective, the study aims to determine crop evapotranspiration to schedule irrigation practices more precisely and optimize water usage in Guilan province, Iran. A total of 120 soil samples were collected from within the study area to measure the soil physical and hydraulic properties. Additionally, meteorological data were acquired from four weather stations across the study area, and the Penman-Monteith method was used to estimate the reference potential evapotranspiration. To determine the standard crop evapotranspiration, crop coefficients were applied. Spatial variability of soil properties and gross irrigation water requirements were analyzed using geostatistical techniques, and spatial distribution maps were constructed in order to determine irrigation management zones using fuzzy k-means clustering algorithm. The estimated standard crop evapotranspiration varied from 572 to 597 mm. In terms of gross irrigation water requirements, a significant variability emerged, ranging from 710 to 1082 mm. Utilizing the geostatistical techniques and the fuzzy k-means clustering algorithm, the study successfully identified four distinct irrigation management zones. Irrigation management zone 1 was characterized by regions with lower gross irrigation water requirements and commendably high water productivity. Conversely, irrigation management zone 4 encompassed areas with relatively lower water productivity and higher gross irrigation water needs. The results underscore the effectiveness of site-specific irrigation management within the studied paddy fields and highlight the necessity for tailored irrigation strategies to enhance water efficiency and productivity.