Relationships between air relative humidity and soil temperature in open-field tomato production

M. Dallev¹ and G. Hristova²*

¹Agricultural University of Plovdiv, 12 Mendeleev Blvd, BG4000 Plovdiv, Bulgaria
²Trakia University, Faculty of agriculture, Department of Agricultural Engineering, Student City, BG6000 Stara Zagora, Bulgaria
*Correspondence: galina_jam@yahoo.com

Abstract:

Understanding microclimatic interactions between atmospheric and soil parameters is essential for precision agriculture and irrigation management. The present study evaluated the relationships between air temperature, relative humidity, soil temperature, and soil moisture under open-field tomato production using a portable ESP32-based monitoring system. Measurements were conducted at ten field points with three replicates per point (n = 30). Descriptive statistics indicated relatively stable environmental conditions during the observation period. Pearson correlation analysis revealed a statistically significant inverse relationship between air relative humidity and soil temperature (r = -0.376, p = 0.040), while no significant linear relationships were observed between the remaining variables (p > 0.05). Linear regression analysis confirmed that increasing air relative humidity was associated with decreasing soil temperature (R² = 0.142, p = 0.040), although the explanatory power of the model remained limited. Validation against a Meteobot® reference weather station demonstrated high accuracy of soil temperature measurements (relative error 0.74%) and acceptable performance for soil moisture (6.28%). The results indicate that low-cost IoT-based monitoring systems can reliably capture microclimatic interactions under field conditions and support their application in precision agriculture.

Key words:

Re-evaluating temperature thresholds for growth and nutrient uptake in winter cereals in Estonia: a review of air-soil temperature dynamics

T. Saue, M. Kärp and K. Tamm

Centre of Estonian Rural Research and Knowledge, Department of Agricultural Research J. Aamisepa 1, Jõgeva Township, EE48309 Jõgeva County, Estonia
*Correspondence: triin.saue@metk.agri.ee

Abstract:

This study re-evaluates the agronomic validity of temperature thresholds for cereal growth and nutrient uptake in cool-temperate agroclimates. By integrating a physiological review with a spatiotemporal analysis of Estonian air temperature records (1965–2024), we assess the potential for phenological mismatch between atmospheric warming and soil thermal readiness.

Our analysis reveals a significant advancement in the onset of the thermal growing season, particularly in South-Eastern Estonia, where spring now begins approximately 10 days earlier compared to the 1965–1990 baseline.

Synthesizing these trends with established principles of soil thermal inertia, we identify a potential increase in the risk of ‘false springs’, where atmospheric signals trigger vegetative growth while soil conditions remain restrictive. Published evidence indicates that nutrient uptake is kinetically constrained in cool soils: nitrogen uptake becomes effective only at soil temperatures of +8–10 °C, and phosphorus uptake is critically limited by low diffusion rates and suppressed mycorrhizal activity, whereas potassium uptake is comparatively less sensitive.

We suggest that under increasingly variable climatic conditions, relying solely on the standard +5 °C air temperature threshold may lead to premature fertilisation and nutrient losses. Therefore, agronomic decision-making in Northern Europe may need to increasingly account for the hysteresis between rapid atmospheric warming and slower soil thermal activation.

Key words:

base temperature, Estonia, heat stress, nitrogen, Phosphorus, potassium, soil temperature, thermal growing season, winter cereals