湖南主要耕地土壤固定态铵含量与最大固铵容量的剖面变化特征

The Distribution Pattern of Fixed Ammonium Content and Maximum Capacity of Ammonium Fixation in Major Types of Cultivated Upland Soils and Paddy Soils in Hunan Province,China

通过野外调查取样、室内培养试验和分析测定,研究了湖南主要旱地土壤和稻田土壤固定态铵含量与最大固铵容量的剖面变化特征及其影响因素.结果表明:(1)水田土壤剖面中固定态铵含量大致有3种变化模式:固定态铵含量随剖面深度的增加而升高,固定态铵含量随剖面深度的增加而减少以及亚表层固定态铵含量明显增大或减少;旱地土壤剖面中固定态铵含量大致有2种变化模式:大部分土壤剖面中固定态铵含量在0～40 cm无明显变化,在40 cm以下固定态铵含量明显升高;少数土壤剖面中固定态铵含量无明显的垂直变化,比水田土壤固定态铵含量的垂直变化要小得多.土壤固定态铵占土壤全氮的相对含量均随深度增加而增大:水田土壤表层(0～20 cm)平均为(15.1±6.6)%,亚表层(20～40 cm)为(25.9±11.7)%,表下第三层(40～75 cm)为(34.6±16.3)%;旱地土壤表层(0～20 cm)平均为20.6%;亚表层(20～40 cm)为32.4%;表下第三层(40～75 cm)为48.2%.(2)水田土壤剖面中土壤最大固铵容量仅2种变化模式:随剖面深度的增加而升高以及亚表层最大固铵容量均大于表层及表下第三层;旱地土壤剖面中最大固铵容量随深度的变化无一定规律,但同一土壤剖面中上下土层最大固铵容量的差异均较水田土壤小.(3)土壤粘粒含量和粘土矿物组成是决定土壤固定态铵含量及最大固铵容量的两个主要因素.供试水田土壤粒径<0.02 mm粘粒中2∶1型粘土矿物以水云母为主,其中,0.002～0.02 mm粘粒的水云母含量远高于粒径<0.002 mm粘粒的水云母含量.相关分析表明,水田土壤的固定态铵含量和最大固铵容量均与粒径<0.02 mm粘粒的2∶1型粘土矿物总量和水云母含量以及粒径0.002～0.02 mm粘粒的2∶1型粘土矿物总量和水云母含量均呈极显著或显著正相关,表明供试土壤的固铵基质主要是粘粒中的水云母矿物.

The distribution pattern of fixed ammonium and maximum capacity of ammonium fixation in the profiles of several cultivated upland soils and paddy soils in Hunan province, China, and their influencing factors were studied with sampling on fields, and laboratory incubation and determination. The main results are summarized as follows： 1.The vertical change of fixed ammonium in profiles of the test soils varied with the soil types. There are 3 patterns in profiles of the paddy soils, i.e., fixed ammonium content increased with increasing depth in the profile of alluvial sandy soil; it decreased with increasing depth in the profiles of gray clayey soil, reddish yellow clayey soil and granitic sandy soil; it was maximum or minimum in subsurface horizon of the profiles of yellow clayey soil, purple clayey soil and newly laky clayey soil. There are only 2 patterns in profiles of the upland soils, i.e., In the profile of 0-40 centimeter depth, the content of fixed ammonium is little changed, and it increased of had no distinct change in the profile of 40- 75 centimeter depth.The percentage of fixed ammonium to total N in soils always increased with the increase of depth： for the paddy soils; it was （15.1±6.6）%, （25.9±11.7）% and （34.6±16.3）% in average in the surface horizon, in the subsurface horizon and in the third horizon, respectively; for the cultivated upland soils, it was 20.6%, 32.4% and 48.2% in average in the surface horizon, in the sabsurface horizon and in the third horizon, respectively. In profiles of the soils, the maximum capacity of ammonium fixation changes vertically at random.Generally the difference in the maximum capacity of ammonium fixation of different horizon in profiles of the upland soils is less than that of the paddy soils because of weaker leaching in profiles of the upland soils： 4.The clay content and clay composition of the tested soils are the two important factors influencing their fixed ammonium content and maximum capacity of ammonium fixation.The 2 ： 1 type clay mineral in 〈 0.02 mm clay of the. paddy soils is predominant in hydrous mica. Of which, the hydrous mica content of 0.002-0.02 mm clay is much higher than that of 〈0.002 mm clay of the soils. The statistic analysis showed that both the fixed ammonium content and the maximum capacity of ammonium fixation of the paddy soils were positively correlated with the total 2 ： 1 type clay mineral content and hydrous mica content of 〈 0.02 mm clay and 0.002 -0.02 mm clay in the paddy soils at the significant level of P001 or P0.05, respectively, but not correlated with the total 2 ： 1 type clay mineral content and hydrous mica content of 〈0.002 mm clay significantly.It demonstrated that the ammonium-fixing matrix of the tested soils mainly exists in the 0.002-0.02 mm clay.