Detecting soil temperature trends in Northeast Iran from 1993 to 2016

Soil temperature is a fundamental agrometeorological variable which has a measureable influence on the development of plants. A comprehensive analysis of daily soil temperature trends at predetermined depths can provide a quantitative understanding for the sustainable management of agricultural systems, such as mitigating the adverse effects of anticipated temperature stress, supporting confidence levels of ideal seed sowing dates, as well as irrigation treatment durations and intervals. In this paper, daily soil temperature trends were analyzed (using the Mann-Kendall test) at depths of 5, 10, 20, 30, 50 and 100cm at seven discrete meteorological stations located throughout northeastern Iran during a consecutive period from 1993 to 2016. The results of this research indicate that in most of the study stations there exists a non-significant negative trend in soil temperature in the first half of January and also in the second half of December; these trends become significant as the soil gets deeper. For the warmer months of the year, especially from April to the end of August, soil temperature trends are positive and significant (or near significant) and these positive trends are of greater significance with a corresponding increase in soil depth. Agri-environmental agencies and practitioners may benefit from the approach used in this research (i.e. using the Mann-Kendall test to analyze trends in daily soil temperature time series) since it is an easily transferable approach that can provide a comprehensive geospatial and temporal analysis of crop and plant patterns in different regions and environmental conditions. Additionally, farmers may use daily soil temperature trends as a means to encourage the protection and mitigation of a variety of projected environmental stresses, such as water scarcity, irrigation demands, seasonal temperature fluctuations, and redundant crop rotation.