玉米大豆根茬混合后的腐解特性

玉米/大豆套作可显著提高粮食产量和养分利用效率。研究间套作作物根茬分解、养分释放规律及其对土壤生物学特性的影响,对阐释该系统中作物养分高效利用具有重要意义。本研究采用室内培养方式,控制根茬总量为2%(2 g根茬+98 g土壤),分别设置单独的大豆根茬(S)和玉米根茬(M)及两种根茬按3∶1、1∶1和1∶3混合(分别表示为SM 3∶1、SM 1∶1和SM 1∶3)共5个不同根茬配比处理和1个不加根茬处理(CK),动态测定根茬矿化速率,碳、氮含量和土壤微生物量碳等指标。研究结果表明:培养前9 d,根茬矿化速率最快,而后矿化速率逐渐降低,到培养60 d后所有处理根茬矿化速率趋于稳定。整个培养周期内玉米根茬CO_2累积释放量显著高于大豆根茬处理,但SM 1∶3处理的CO_2累积释放量始终高于其他处理。培养结束后,SM 1∶3处理的有机碳矿化量显著高于其他处理。根茬总碳含量在前10 d无显著变化,10~60 d时显著降低,后趋于平稳。培养结束后SM 1∶3处理的根茬碳含量相比初始值降低最多,降幅达到24.8%,其次是玉米根茬(M)处理,降幅为21.4%,大豆根茬(S)处理碳含量降低最少,为9.7%。根茬总氮含量在前10 d显著降低,10~100 d总氮含量显著增加。培养结束后大豆根茬(S)总氮含量最高,SM 1∶3处理总氮含量最低。土壤微生物量碳含量在培养周期内呈先增加后降低而后趋于平稳的变化规律。培养结束后与CK相比,SM 1∶3、SM 1∶1、M、S和SM 3∶1处理的土壤微生物量碳含量分别增加89.4%、58.8%、47.1%、41.2%和37.5%。因此,玉米、大豆根茬混合后在土壤中的矿化速率、养分释放速率明显高于单一根茬处理,且有利于土壤微生物的繁殖。在本试验所选的3种配比中,SM 1∶3的配置效果最佳。

Decomposition characteristics of mixed maize and soybean root residues

Maize/soybean intercropping system could potentially improve crop yield and nutrient-use efficiency. It is pivotal to elucidate nutrient efficiency of crop root residue decomposition, nutrient release and the related effects on soil biological characteristics in intercropping processes. In this laboratory incubation study, we set different combined ratios of maize and soybean root residues, including sole soybean (S), sole maize (M) root residues, S:M=3:1(SM 3:1), S:M=1:1 (SM 1:1), S:M=1:3 (SM 1:3), with soil without residues (CK) as the control. The ratio of total weight of residues to soil in each treatment was 2:98, in unit of gram (g). We dynamically measured the mineralization rate of residues, contents of total carbon and nitrogen of remained root residues and SMBC (soil microbial biomass carbon) content. The results showed that the mineralization rate of root residues was fastest during 0-9 days after incubation, which then gradually decreased after 9 days. After 60 days of incubation, the mineralization rate of root residues in all the treatments stabilized. During the whole incubation period, the cumulative release of CO₂ from maize roots was higher than that from soybean roots, but the cumulative release of CO₂ under SM 1:3 treatment was always higher than the other treatments. The cumulative release of CO₂ under SM 1:3 treatment was significantly higher than that under other treatments at the end of incubation. The content of total carbon in root residues had no significant change in the first 10 days, but decreased significantly during 10-60 days of incubation, after which it stabilized. At the end of incubation, total carbon content under SM 1:3 treatment decreased by a maximum of 24.8% from the initial value, followed by maize root residue treatment (which decreased by 21.4%), and the decrease in carbon content of the soybean root residue treatment was minimum, which was 9.7%. Total nitrogen content decreased significantly in the first 10 days of incubation, and then increased significantly until the end of incubation. Total nitrogen content of soybean root residues was highest at the end of incubation, and SM 1:3 treatment had the lowest. SMBC content first increased and then decreased during the incubation, followed by a steady change. At the end of incubation, SMBC content of SM 1:3, SM 1:1, M, S and SM 3:1 were 89.4%, 58.8%, 47.1%, 41.2% and 37.5% higher than CK, respectively. Hence, the mixtures of maize and soybean root residues had higher mineralization and nutrient release than sole maize and soybean root residues. This was beneficial to the reproduction of soil microorganisms. Among the three ratios selected in this experiment, the SM 1:3 had the best effects.