Soil Organic C:N vs. Water-Extractable Organic C:N

Abstract

Traditionally, soil-testing laboratories have used a variety of methods to determine soil organic matter, yet they lack a practical method to predict potential N mineralization/immobilization from soil organic matter. Soils with high micro-bial activity may experience N immobilization (or reduced net N mineralization), and this issue remains unresolved in how to predict these conditions of net mineralization or net immobilization. Prediction may become possible with the use of a more sensitive method to determine soil C:N ratios stemming from the water-extractable C and N pools that can be readily adapted by both commercial and university soil testing labs. Soil microbial activity is highly related to soil organic C and N, as well as to water-extractable organic C (WEOC) and water-extractable organic N (WEON). The relationship between soil respiration and WEOC and WEON is stronger than between respiration and soil organic C (SOC) and total organic N (TON). We explored the relationship between soil organic C:N and water-extractable organic C:N, as well as their relationship to soil microbial activity as measured by the flush of CO<sub>2</sub> following rewetting of dried soil. In 50 different soils, the relationship between soil microbial activity and water-extractable organic C:N was much stronger than for soil organic C: N. We concluded that the water-extractable organic C:N was a more sensitive measurement of the soil substrate which drives soil microbial activity. We also suggest that a water-extractable organic C:N level > 20 be used as a practical threshold to separate those soils that may have immobilized N with high microbial activity

Impact of Management Practices on Water Extractable Organic Carbon and Nitrogen from 12-Year Poultry Litter Amended Soils

“…Haney et al [28] compared soils from the Riesel study to soils collected from agricultural fields in Idaho, Georgia, Maine, Mississippi Oklahoma, Texas, and Wyoming to understand the relationship between soil organic C:N and WEOC:WEON. They concluded that the WEOC:WEON ratio was a more sensitive measurement than total C:N because of the direct influence of soluble C and N on microbial metabolism.…”

Spatial Analysis and Modeling the Nitrogen Flush after Rainfall Events at the Field Scale in SWAT

“…The interactions between the biology of the soil and the inorganic components of the soil are predictable and can be easily modeled using the soil test data we obtained. Haney et al (2012) found that soil microbial activity measured as the flush of 1-d CO 2 following rewetting of dried soil was significantly correlated to WEOC and WEON. Figure 3 depicts the relationships between 1-d CO 2 , WEOC and WEON values for various soils throughout the contiguous United States (data from USDA-ARS).…”

“…Figure 3 depicts the relationships between 1-d CO 2 , WEOC and WEON values for various soils throughout the contiguous United States (data from USDA-ARS). Short-term C respiration from soil after drying and rewetting is also highly correlated with soil microbial biomass C and 24-d N mineralization (Haney et al, 2012). The laboratory Drying and Rewetting (D/R) process mimics the natural processes in the field that occur with rainfall events, the extent of which depends upon climatic and soil conditions.…”

Land Productivity Enhancement by Sulfur Nutrient Management in Vertisol Rice Field

“…Organic matter content in the soil is closely related to soil N content. It was reported by Haney et al (2012) that the N and C-organic soil content had a close correlation (r 2 =0.93), and so did between N and the water extracted C-organic (r 2 =0.84) on farms of Idaho, Georgia, Maine, Mississippi, Oklahoma, Texas and Wyoming. N is a mobile nutrient and easily lost through evaporation, leaching and lateral flow.…”