Abstract: An automatic measurement system of microclimate gradients was employed to observe photosynthetically active radiation (PAR), air temperature, tree body temperature, relative humidity at different heights of 6, 3 and 1.5 meters, and total radiation atop the canopy and soil temperature and humidity from 10 to 60 cm with intervals of 10 cm in an apple orchard on the Loess Plateau from January 2011 to December 2013. The microclimate characteristics of the apple orchard at different growth stages were investigated. The results showed that the total radiation, PAR, air temperature and tree body temperature all presented an obvious diurnal variation with one peak. The total radiation and PAR peaked at 12:50, air temperature and tree body temperature peaked around 16:00. The total radiation and PAR reached maximum at vigorous growth stage and second at initial growth stage. The air temperature, tree body temperature and soil temperature reached maximum at vigorous growth stage, and came second at initial growth stage. PAR atop the canopy was greater than that beneath the canopy at vigorous growth and dormant stages. The vertical variation of air temperature was greatest at dormant stage, and next at vigorous growth stage. Except at the surface, soil temperatures increased with the depth, accompanying a smaller diurnal variation. Humidity was maximum at vigorous growth stage, and next at dormant stage, and its maximum daily difference occurred at initial growth stage and came second at vigorous period. Humidity was higher beneath canopy than atop canopy during night, especially at vigorous growth stage. Soil moisture was highest at initial growth stage and next at vigorous growth stage. It was lower in the surface and deep layers, and reached maximum at 20 cm depth with a great variation.

Key words: straw incorporation, bulk density, tillage, humification coefficient, soil organic carbon