微生物商对亚热带地区土地利用及施肥制度的响应

Response of C_(mic)-to-C_(org) to Land Use and Fertilization in Subtropical Region of China

【目的】土壤微生物商对于土壤质量的变化具有重要的指示意义,本文探讨其在中国亚热带土壤中应用的可靠性与灵敏性。【方法】利用2个典型小区域和6个长期定位试验结果,分析了土壤微生物商对于土地利用方式(水田、旱地、果园、林地)和稻田施肥制度的响应。【结果】盘塘样区中稻田土壤微生物商平均为(5.07±1.26)%,旱地土壤微生物商为(2.96±1.60)%,高于林地的(2.40±0.34)%,果园土壤微生物商仅为(1.98±0.89)%。肯福样区情况略有不同,其各土地利用方式下土壤微生物商均明显低于盘塘样区,稻田(3.01±1.51)%>林地(1.57±0.40)%>旱地(1.29±0.56)%>果园(1.14±0.42)%。施肥方式的变化,尤其是有机肥的施用也对土壤微生物商产生了明显的影响。长期定位试验中化肥在半数稻田监测点上提高了土壤微生物商;中量和高量有机肥平均使稻田土壤微生物商提高了17.94%和19.91%,作用优于化肥单施;秸秆处理作用与中量有机肥接近,土壤微生物商提高17.51%。但无论是小区域还是长期定位试验中土壤微生物碳与有机碳相关分析结果均表明,尽管二者具有显著的相关关系,但土壤微生物商与期望值的差异变化很大。【结论】结合区域调查和长期施肥试验,可以认为土壤微生物商基本可以反映土地利用和施肥尤其是有机肥投入变化对土壤质量影响的趋势,但由于不同情况下其变化趋势与有机碳的反应不完全一致,因此在使用时应谨慎。此外,中国亚热带地区稻田土壤微生物商较高,说明稻田具有较高的微生物生物量维持能力。

[Objective] Ratios of microbial biomass C to total organic C （Cmic-to-Corg） could be an indication of a system at a new equilibrium after land use or managements changed. [ Method ] But few researches putted their emphasis on the impacts of land use or management on Cmic-to-Corg. TWO small-scaled regions （Pantang region and Kenfu region） and six long-term experiments （1986-2001） in paddy fields were used to investigate the response of Cmic-to-Corg to land use and fertilization in subtropical region of China. [Result] The results from PT and KF regions indicated that there was no universal equilibrium Cmic-to-Corg constant in every land use. Mean Cmic-to-forg amounted to （5.07±1.26）% for paddy field, （2.96±1.60）% for dryland, （2.40±0.34）% for woodland, （1.98±0.89）% for orchard in Pantang region, respectively. The effect of land use on Cmic-to-Corg in Kenfu region was a little different with that in PT region. Mean Cmic-to-Corg amounted （3.01 ±1.51）% for paddy field, （1.57±0.40）% for woodland, （1.29± 0.56）% for dryland, （1.14±0.42）% for orchard, respectively. In both regions, responses of Corg to land uses were similar with Craig-to-Co,g, and the results also showed that anthrostagnic soil （paddy field） was not only in favor of the carbon sequestration but also helpful to the microbial biomass enhancement. Long-term experiments showed that Cmic-to-Corg of paddy soils with chemical fertilizer applied increased in recent 17 years in half of experiments but not significant. With the same amount of N applied, organic matter incorporation including middle-level （30% organic N＋70% chemical N） manure, high-level （60% organic N＋40% chemical N） manure and straw treatments contributed to the enhancement of microbial biomass in paddy soils, averaged by 6 experiments,Cmic-to-Corg increased by 17.94%, 19.91% and 17.51% （compared with control）, respectively. [Conclusion] Though significant relationships （P〈0.01） exists between organic C and microbial biomass C in 6 long-term experiments, but the response of soil organic C to fertilization was not completely the same as that of Cmic-to-Corg. It indicated that Cmic-to-Corg could reflect the changes of Corg, but not precisely.