Horizontal Variability and Diurnal Fluctuation of Soil Respiration in Corn and Soybean Rows

This study evaluated the horizontal variability and diurnal fluctuation of soil respiration to accurately capture changes in carbon flux during agricultural production in Lishu County, Jilin Province, China. Corn (Zea mays L.) and soybean (Glycine max L.) were planted with 60-cm row spacing in 2020. The soil respiration rate (SRR) was measured at 2-hour intervals on July 1, August 1, and September 25 using a portable, closed chamber at five positions, P0, P15, P30, P45, and P60, denoting specific distances from the crop rows. The SRR between crop rows was affected both by dates and fields with the coefficient of variation ranging between 7.1 and 37.7%. The SRR at P45 was closest to the mean SRR, with a relative deviation of 0.09-4.85% on July 01 and August 01 in corn and soybean fields. On September 25, the optimal position to measure SRR was between P45 and P60. The sampling dates influenced the optimal time for measuring SRR but were mostly concentrated between 9:00 and 11:00 (24-hour clock) for corn and between 11:00 and 13:00 for soybean. The root biomass of crop rows and diurnal soil temperature were the main factors affecting horizontal variability and diurnal fluctuation of SRR, respectively. We recommend an SRR sampling strategy at P45 between 9:00 and 11:00 for corn and between 11:00 and 13:00 for soybean to decrease the effects of horizontal variability and diurnal fluctuation of SRR.