Influence of drip irrigation uniformity on buried position of soil moisture sensor

Abstract: Prior to adopting the wireless sensor network system to schedule the irrigation, one of the key problems needing to be resolved is developing the placement criteria for soil moisture sensors to decrease the measurement density and investment. In this study, the temporal stability of soil water content was used to guide the sensors to be placed in the positions directly representing the plot-average soil water content. The influences of drip irrigation uniformity on spatial distribution uniformity and temporal stability of soil water content were also investigated to analyze the choosing probability of buried locations for soil moisture sensors with different drip irrigation uniformity. This field study was conducted at the experimental station of China Institute of Water Resources and Hydropower Research in Daxing District, Beijing City in 2011 and 2012. During the growing season of spring maize, the effective rainfall was 356 and 381 mm in 2011 and 2012, respectively, and irrigation was applied 4 times in each year. The low, medium and high drip irrigation uniformity, corresponding to the Christiansen uniformity coefficient (Cu) of 0.60, 0.80 and 0.97, respectively, were used in the irrigation of the spring maize. The low and medium Cu values were obtained by randomly assembling segments of drip tubes with 5 different nominal discharge values (1.05, 1.4, 1.65, 2.3, and 2.6 L/h at 0.1 MPa) along the entire length of the line. A temporal stability analysis of soil water content was conducted by regularly measuring soil water contents at 54 locations in the ?eld during the growing season of maize. Results indicated that the uniformity coefficient of soil water content was bigger than 0.81 in all treatments and it decreased with the decreasing of drip irrigation uniformity. The average Spearman's rank correlation coefficient was significant at the probability level of 0.05 in all treatments, while the structure similarity of soil water content distribution decreased with the increasing of irrigation uniformity. The soil water content in all measurement points has great temporal stability within and between experimental years. In the high drip irrigation uniformity treatment, the percentage of positions directly representing the mean soil water content was 83%, 78%, 53%, and 86% in layer of 0-0.2, >0.2-0.4, >0.4-0.6, and >0.6-0.8 m, respectively, and it decreased with the decreasing of drip irrigation uniformity. The experimental results demonstrated that the buried locations for soil moisture sensors can be determined only through one-year study, and its choosing probability is lowered with the decreasing of drip irrigation uniformity.