| Based on 12 years of long-term located conversation tillage and residue returning farmland(started in 2002), this study was implemented in Agricultural Experiment Station of Shandong Agricultural University in 2013 and 2014. We systematically explored the effects of long-term different tillage methods in winter wheat season(C: conventional tillage, N: no tillage, S: subsoiling and R: rotary tillage) with residue returning(P: residue returning and A: no residue returning) on summer maize soil microbial properties and organic carbon fractions. We Combined field in-situ monitoring with laboratory incubation, systematically analyzed the influence of different residue returning and wheat season tillage on summer maize soil microbial properties and organic carbon fractions. And we analyzed the effects of different temperature(25, 30, 35?), moisture(55%, 65%, 75%) and the organic material addition(adding residue, on adding residue) indoor training on soil respiration and soil organic carbon(SOC) content. Thus, we could make clear the contribution of organic materials on soil CO2 release and SOC to screen out the best tillage combination. The main results were as follows: 1. Changes of soil respiration and microbial characteristics under different residue returning and tillage methodsConcentration profile of CO2 has been well documented that the soil CO2 concentration of each treatment increased with increasing soil layer depth in addition to the 0-10 cm soil layer in this experiment. In the 0-40 cm layer, soil CO2 concentration in jointing stage and Bell-mouthed stage were higher than that in other periods. While soil CO2 concentration appeared peak at anthesis and filling stage as the increase of soil depth. The CO2 concentration in soil profile of residue returning treatments were slightly higher than that treatments without residue, and the difference became smaller with the increase of soil depth. Residue returning could improve soil respiration in jointing stage and flowering stage and reduce soil respiration in Bell-mouthed stage, filling stage and mature stage. In the 0-40 cm soil layer, the CO2 concentration of subsoiling and no tillage was higher than that of conventional tillage and rotary tillage, while no tillage was more active in the 40-200 cm soil layer.Residue returning and conservation tillage mainly affected the soil microbial characteristics in 0-10 cm soil layer. Residue returning could significantly improve the soil microbial biomass carbon(MBC) and microbial activity, reduce the respiratory quotient(q CO2). Under the same residue treatment, subsoiling and no tillage can significantly reduced soil respiration and respiratory quotient than conventional tillage and enhance the MBC and microbial activity. Through the whole growing period, residue returning with conservation tillage could significantly increase the MBC and microbial activity and reduce the respiratory quotient. In the 0-10 cm soil layer, compared with conventional tillage without residue returning, the MBC of subsoiling and no tillage with residue returning was significantly increased by 95.81% and 74.28% respectively and the microbial activity increased by 97.05% and 74.23%. 2. Changes of SOC and its fractions under different residue mulching and tillage methodsSOC and its fractions content in the distribution of farmland soil in 0-10 cm soil layer was more than that in 10-20 cm soil layer. Besides conventional tillage, the percentage of readily oxidizable carbon(ROC) to SOC and microbial quotient in the 0-10 cm soil layer were higher than in 10-20 cm layer. Conservation tillage soil showed obvious “upper rich lower poor”. Residue returning could significantly improve SOC, ROC and MBC content in 0-10 cm soil layer. Subsoiling and no tillage could significantly increase SOC content and increase ROC and MBC. In the 0-10 cm soil layer, the percentage of ROC to SOC was about 29.47-41.11% and microbial quotient was 4.56-6.16%. The percentage ROC to SOC of PN was the highest and reached to 41.11%. Microbial quotient of PS and AS was the highest and reached to 6.16%. After 12 years continuous conservation tillage, subsoiling with residue returning could significantly increase the content of SOC and its fractions, and the next is no tillage with residue returning treatment. 3. Effects of different temperature, moisture and residue addition on soil respiration, organic carbon and MBCBased on three different tillage(conventional tillage, no tillage, subsoiling tillage) soil with different temperature, humidity and carbon source add training, we concluded that adding carbon source could increase the release of soil CO2, SOC and MBC content significantly. Lower temperature and lower humidity incubation could significantly decrease soil respiration rate and soil CO2 cumulative evolution and reduce the consumption of SOC. Adding residue could maximize increase the soil MBC content after 35? incubation. Subsoiling organic carbon content was higher than other treatments before incubation and after residue addition culture it was still the highest. MBC of conventional tillage was higher than other treatments before incubation, while subsoiling MBC was the highest after residue addition cultivation. Subsoiling could increase SOC and MBC in the 55% humidity, while conventional tillage and no tillage would require a higher humidity. Subsoiling at 25? culture was most conducive to the accumulation of SOC and was more conducive to the accumulation of MBC at 35? culture. With the lower humidity(55%) and carbon source added incubation, subsoiling is most conducive to accumulate and improve organic carbon and MBC. 4. Effects of residue mulching and tillage methods on crop yield and yield componentsExcept for the AC and AR, the maize production in 2014 was rise compared with AC in 2013. 1000 grain weight of residue returning treatment was higher than no residue. 1000 grain weight of subsoiling and no tillage were higher than that of conventional tillage and rotary tillage. The grain number was significantly different in different treatments. Average annual output of residue returning treatments were higher than that of no residue by 9.53%. The output of subsoiling and no tillage treatment were higher by 16.11% and 6.11% respectively than conventional tillage. And rotary tillage appeared slight yield. The correlation between yield and 1000 grain weight was positive.Combining the field situ monitoring with indoor simulation analysis, we concluded that soil CO2 concentration increased with increasing soil layer depth. Residue mulching could significantly improve soil CO2 release, while increasing SOC, ROC, MBC and microbial activity. Long-term subsoiling and no tillage could reduce soil respiration, improve soil microbial activity, increase SOC and fractions content than conventional tillage. Subsoiling and no tillage could fully increase SOC content in lower humidity and residue addition incubation. Subsoiling could significantly increase soil MBC at 35? and 55% humidity with carbon source addition. Residue returning combined with wheat conversation tillage could improve soil microbial activity and reduce q CO2, increase soil readily oxidation carbon, MBC and organic carbon content, increase ROC to SOC ratio and microbial quotient, improve soil ecological factors. Compared with other treatments, the subsoiling with residue returning was the best tillage combination. |
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