Analysis of soil respiration and the influencing factors in soybean fields under conservation tillage

The effects of conservation tillage on soil respiration in dry croplands were investigated in the southwest purple hilly region. The LI6400-09 respiratory chamber was used in the experiment conducted in the experimental field of Southwest University, Beibei, Chongqing. The respiration, hydrothermal and biotic factors of soil were measured and analyzed during soybean growth period in a wheat-maize-soybean triple intercropping system. There were six treatments and each treatment replicated three times. The treatments included traditional tillage (T), ridge tillage (R), traditional tillage + straw mulching (TS), ridge tillage + straw mulching (RS), traditional tillage + straw mulching + decomposing inoculants (TSD) and ridge tillage + straw mulching + decomposing inoculants (RSD). The results suggested that soil respiration rate initially increased slowly after planting. It then increased rapidly at blossoming stage and decreased steadily at maturity of soybean. Differences were noted in soil respiration rate among different treatments and soil respiration order was T < R < TS < RS < TSD < RSD. Ridge tillage and straw mulching improved soil respiration in soybean fields. Soil temperature in 10 cm soil layer was in the order of T > TSD > TS and R > RSD > RS. Q₁₀ value, a sensitive indicator of soil respiration to temperature, was in the order of TS > TSD > RS = R > T > RSD. Q₁₀ increased under straw mulching, but the opposite occurred under ridge tillage. Soil moisture order in 5 cm soil layer was TSD > RSD > TS > RS > T > R. Soil respiration and soil moisture had parabolic function relationship, with significant correlation coefficient under R treatment. Other treatments showed negative correlations, with an extreme significant level under TS treatment. The dominant groups of soil animals in soybean fields included Collembola, Acarina and Diptera. There was no significant correlation between soil respiration and soil animals captured by tullgren apparatus and pitfall traps method. When the soil animals numbers captured by two methods were added together, the correlation coefficient under T was significant (R = 0.901 at P = 0.037).