Skip to main content
ARS Home » Pacific West Area » Pendleton, Oregon » Columbia Plateau Conservation Research Center » Research » Publications at this Location » Publication #83993
Title: LIGHT FRACTION SOIL ORGANIC MATTER IN LONG-TERM AGROECOSYSTEMS

Author
item Albrecht, Stephan
item BAUNE, HEATHER
item Rasmussen, Paul
item Douglas Jr, Clyde

Submitted to: Pendleton Station Field Day
Publication Type: Experiment Station
Publication Acceptance Date: 4/22/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Soil organic matter includes plant, animal and microbial material in all stages of decay. It plays a major role in maintaining soil structure, water infiltration, root development, and the reduction of soil erosion. Soil organic matter quality can be estimated by the characterization of a light fraction. The light fraction is material that will float on the top of dense salt solution. The light fraction is generally considered to be material rich in plant nutrients, relatively large in size compared to other soil organic matter components and insoluble in water. It has been suggested that the light fraction provides a reliable indication of the end result of soil management. The objectives of this investigation were to isolate the light fraction from the soil of several long-term experiments and evaluate the relationship of the light fraction of the soil organic matter to long-term management practices. The proportion of light fraction recovered from whole soils ranged from 0.04 percent in a soil from a plowed field to 0.61 percent in a grass pasture soil. The amount of light fraction decreased with depth in all management practices. The main relationships were: (a) continuous grassland has greater light fraction accumulation than does cultivated soil; (b) no-till management results in greater light fraction accumulation than does plowing and burning; and (c) there is an inverse relationship between light fraction and soil depth and a positive relationship between light fraction and nitrogen fertilization. It was shown that the concentration of

Technical Abstract: Soil organic matter includes plant, animal and microbial material in all stages of decay. Soil organic matter plays a major role in maintaining soil structure, soil water infiltration, root development, and reducing soil erosion. The accumulation of soil organic matter is dependent on the balance between primary productivity and biological decomposition of residue. It has been suggested that the proportion of the light fraction (material with a density of less than 1.7 g/cc) of soil organic matter provides a reliable indication of the consequences of soil management. The objectives of this investigation were to isolate soil organic matter light fraction from the soil of several long- term experiments at the Pendleton Agricultural Research Center and evaluate the relationship of soil organic matter light fraction to long-term management practices. The light fraction was isolated, using the method of Gregorich and Ellert from soil samples collected from long term experiments. The proportion of light fraction recovered from whole soils ranged from 0.04 percent in soil under conventional tillage to 0.61 percent in a grass pasture soil. The amount of light fraction decreased with depth in all management practices. The C:N ratio in the light fraction ranged from almost 10 to slightly over 23. The concentration of soil organic matter light fraction was distinctly different among cropping systems and a will provide a key indicator of management practices that will improve soil quality.