摘要
对土壤有机碳作用的综述研究显示:直至20世纪末,对于土壤有机碳的研究主要集中于阐明具不同化学结构有机物质在土壤中的功能,如胡敏酸、富里酸、黄腐酸的化学结构特征及在土壤肥力中的作用。中欧近年的研究则更关注按照有机碳在土壤中的转化特征进行分组,尝试建立这一分组与土壤有机碳功能的关联。按照转化特征,土壤有机碳可分为稳定性有机碳和营养性有机碳两大类型。前者主要指封存于土壤黏粒中的有机碳,很难被土壤微生物分解和矿化。后者主要指通过作物收获后地表及根系残留物、还田秸秆、有机肥施肥进入土壤的有机碳,是土壤有机碳中易于转化的、活跃的组分,也是形成土壤腐殖质和团聚体的主要前体物质。对土壤肥力具有重要意义。多点长期定位试验研究结果显示:土壤有机碳含量实际上表达了土壤中有机碳输入与分解两个过程的动态平衡。当输入量小于矿化量,将导致土壤有机碳含量和土壤肥力下降。当每年输入的有机碳量大于矿化量,土壤有机碳含量会持续上升;直至每年输入量与矿化量相等,土壤有机碳含量不再增加,此时,土壤有机碳含量达到平衡点。在一般农业生产条件下,达到平衡点的时间周期为20-30年。在营养性有机碳投入量过高情况下,这一动态平衡系统也会导致入多出多,达到新的平衡点后,每年会有高量土壤有机物质的矿化,从而引起农田土壤中矿质养分,特别是矿质氮的流失,进入水体及大气环境中。为实现土壤培肥和环境保护双重目标,农田土壤营养性有机碳的投入量应以有机碳的矿化流失不致产生环境风险为宜。新的研究还证实:营养性有机碳进入农田后,在土壤生物作用下分解为一系列短链化合物,再通过生物构建作用与土壤矿物颗粒形成土壤团聚体,并以此对多项土壤肥力性状发挥积极作用。受土壤中腐殖化、有机碳分解等不同过程影响,土壤团聚体持续发生着聚合和崩解,只有持续而丰富的营养性有机碳输入,才能维持土壤中总有机-无机团聚体的稳定度。多点长期定位试验结果揭示:土壤有机碳含量主要取决于气候条件、土壤质地与土地利用类型。在人为因素中,土地利用方式的变化对土壤有机碳含量的影响最大,而施肥、秸秆还田、耕作等农作措施对土壤有机碳含量的影响比较小。耕地土壤上,作物类型不同,其典型的耕作和收获方式不同,收获后存留地表和土壤中的根系残留物数量和质量不同,有机质生成能力不同。在种植有机质消耗性作物时,需要注意在轮作制度中引入有机质增加型作物或施用有机肥料,以保持土壤肥力。
Up to end of last century,studies on SOC were mainly concentrated in identifying chemical structures of different organic materials in soil,such as structural characteristics of humic or fulvic acids and their related functions for soil quality.In recent years,focus on SOC has been laid on SOC transformation characteristics in soil,trying to establish the relationship between SOC functions and the grouping according to SOC transformation characteristics.According to the transformation properties,SOC can be divided into two groups,including the stable SOC and the active SOC.The first one refers mainly to the SOC closely combined with clay or fine silt and it is difficult to be decomposed and mineralized by soil microorganisms.Stable SOC belongs to passive and inert SOC pool in soil.The second one refers to SOC,which mainly consists of crop residues and roots after harv esting,crop straws returned to farmland and organic manures applied.The active SOC belongs to nutritive and labile SOC pool in soil.This part of SOC is of great importance to soil fertility.SOC concentration is actually the expression of dynamic equilibriu m of two processes.One is the input of organic materials to soil and the other one is the decomposition and mineralization of SOC.When the amount of organic material input is less than the mineralized amount,the SOC concentration and soil fertility will decrease.When the annual input of organic carbon is greater than the annual mineralization amount,the SOC concentration will keep rising until the annual input is equal to the annual mineralized amount.At this moment,SOC concentration will no longer increase and reaches the equilibrium point.Under normal agricultural production conditions,the duration for reaching equilibrium point needs 20 to 30 years.If the active SOC input is in very high level,the dynamic equilibrium system will also lead to a high amount of SOC mineralization annually.In such case,it might lead to a loss of mineral nutrients from soil into water and atmospheric environments,especially mineral nitrogen loss.For the purposes of soil fertility improvement and environmental protection,the active SOC input for farmland should be controlled to the level equal to the annual SOC mineralization amount,sustaining the so-called balance with positive zero.New research shows that the active SOC,after entering soil,is decomposed into a series of short-chain chemical compounds by soil organisms.These short-chain chemical compounds combine with soil mineral particles and form soil organic-mineral aggregates through bioturbation.A lot of soil fertility properties are positively affected b y formation of these aggregates.Influenced by humification,decomposition and other processes of SOC,aggregation and disaggregation in soil occu r simultaneously and consistently.In order to maintain stability of the total aggregates in soil and to increase soil fertility,sustained and abundant active SOC should be inputted to soil.Variation of SOC concentration depends mainly on climate,soil texture an d land use forms.Among the artificial influences,land use form changing has the greatest impact on SOC concentration.In comparison,farming managements,such as fertilization,straw returning,tillage and crop rotation,have much less impacts on SOC concentration.In arable land,crops with different growth periods,tillage and harvesting managements will produce different amounts of above ground residues and root residues after harvesting.Depending on residue quantity and quality,different cro ps are of different capacity for SOC reproduction.According to the differentiated SOC reproduction capacities,field crops can be divided into two types:SOC increasing crops and SOC consuming crops.For farmland with SOC consuming crops,it is very important to introduce SOC increasing crops in rotation or to apply organic manure or organic materials to field,in order to sustain soil fertility.
作者
张维理
KOLBE H
张认连
ZHANG WeiLi;KOLBE H;ZHANG RenLian(Institute of Agricultural Resources and Regional Planning,Chinese Academy of Agricultural Sciences,Beijing 100081,China;S?chsische Landesanstalt für Landwirtschaft,Waldheimer Stra?e 219,D-01683 Nossen,Germany)
出处
《中国农业科学》
CAS
CSCD
北大核心
2020年第2期317-331,共15页
Scientia Agricultura Sinica
基金
科技部科技基础性工作专项(2006FY120200、2012FY112100)