Hysteresis of soil temperature under different soil moisture and fertilizer in solar greenhouse conditions
Soil temperature is one of the important variables in spatial prediction of soil energy balance in a solar greenhouse. The objective of this study was to find a simple method to estimate the hysteresis of soil temperature under three soil moisture and two fertilizer levels in solar greenhouse conditions with tomato crop (Lycopersicon esculentum Mill). The results show that the soil moisture had no significant effects on the soil mean temperature and had significant effects on the soil hysteresis. The mean soil temperature could not express the relationship between the soil temperature and the air temperature accurately due to the soil hysteresis existence, while the correlation between the diurnal variations, air temperature and soil temperature could describe the soil hysteresis. We applied the phase of sinusoidal curve Ti = ̄Ti + Ai sin(ωt − φi ) to best approximate the hysteresis effect of soil temperatures. The soil hysteresis increased with the increase of soil depth, and the hysteresis effect of soil temperature was more and more obvious with the increase of soil moisture and the amount of fertilizer. When forecasting the soil hysteresis, we need to take into account, the change of the diurnal variations, soil temperature, the amplitude of soil temperature and initial phase.
Key words: Soil moisture, fertilizer, soil temperature, solar greenhouse.