Method for variable rate irrigation management zone delineation based on apparent soil electrical conductivity

Abstract: Variable rate irrigation (VRI) technologies could dispatch the specified amount of water to specific locations in the irrigated area, which makes it possible for farmers to address the temporal and spatial variability of the soil and plants within a field. Management zone is an essential part for VRI. It is expected that variable rate application based on scientific management zones would help famers saving water and optimizing yield. Selecting an index that could quickly and accurately characterize soil spatial variability is the key of management zone delineation. In this study, three test fields were used for apparent soil electrical conductivity (ECa) survey in Tongzhou district, Beijing, and Zhuozhou, Hebei Province. The data of ECa in two soil layer depths including 0 to 30 cm (ECash) and 0 to 90 cm (ECadp) was measured by Veris EC 3100 system. In this study, a total of 4 748 and 5 154 data of ECa were obtained before and after tillage in No.1 test field. A total of 3 717 and 5 844 data of ECa were obtained in No. 2 and No.3 test field, respectively. Analyzing by inverse distance weight interpolation and Jenks classification, the ECa maps of three test fields were drawn. Spatial distribution characteristics of ECa were analyzed. The composition of soil texture particles was tested. The average ECa of three test fields mainly varied from 13.20 to 29.25, 2.34 to 5.79, 2.69 to 6.86 mS/m, with the Coefficient of Variations (CVs) of 25.60%, 67.64% and 64.20% for No.1, No.2 and No. 3 test field, respectively. Compared with ECadp, the spatial distribution of ECash changed obviously after tillage in No.1 test field. The ECa value was linearly negatively correlated with the sand content, and linearly positively correlated with silt and clay content. Compared to ECash, ECadp showed stronger linear relationships with soil particle composition, with correlation coefficient of 0.83, 0.90 and 0.86 for sand, silt and clay content, respectively. The ECadp value could indirectly represent the soil texture distribution of field. Furthermore, the high-precision spatial distribution map of ECa could be obtained quickly by Veris EC 3100 system. Therefore, ECadp and its spatial distribution could be used for delineating VRI management zones, especially in the large scale field. No management zone was created in No.1 test field due to relatively low CVs and scattered spatial distribution of ECadp. In contrast, No.2 and No. 3 test fields had relatively high CVs and concentrated spatial distribution of ECadp, which illustrated that No.2 and No. 3 test fields had great potential in developing variable irrigation management. Taking into account the CVs, spatial distribution characteristics of ECadp and VRI control ability of the irrigation system, three management zones were delineated in No.2 and No. 3 test fields. Moreover, software with Java language was developed, which could realize automatically delineation of irrigation management zones after uploading ECa data. The software included interpolation calculation module, management zone division module and variable irrigation control module. The software was validated with the data of the No. 3 test fields. The ranges of each grade, interpolation and spatial distribution of ECa calculated by the software were essentially the same with the analysis result of ArcGIS software. The software not only simplified the calculation process, but also realized the real-time management of variable management zone, which was use-friendly to famers. This study provided a fast, reliable and simple method for the delineation of VRI management zones.