Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2017
Publication Date: 2/26/2018
Citation: Acosta Martinez, V., Cano, A.M., Johnson, J.M. 2017. An approach to determine multiple enzyme activities in the same soil sample for soil health-biogeochemical indexes. Applied Soil Ecology. 126:121-128.
Interpretive Summary: Some agricultural practices may lead to soil degradation. Therefore, soil scientists are looking for indicators of changes on the condition of a soil’s health. A healthy soil has the capacity to cycle plant essential nutrients like phosphorus (P), sulfur (S), nitrogen (N) and carbon (C) using enzymes. The current protocol requires analyzing each enzyme independently as soil health indicators, but requiring more time and resources. However, there is an opportunity to assess these indicators in a more efficient way. Therefore, ARS scientists from Lubbock TX and Morris MN, with a collaborator from Texas Tech University suggest measuring two or more enzyme activities simultaneously in the same soil sample to provide a biogeochemical index. This approach will reduce cost, time, resources and waste generated by half or more, and will benefit producers, action agencies, and soil testing laboratories interested in monitoring and enhancing soil health.
Technical Abstract: Enzyme activities (EAs) are soil health indicators of changes in decomposition processes due to management and the crop(s) affecting the quantity and quality of plant residues and nutrients entering the soil. More commonly assessed soil EAs can provide information of reactions where plant available nutrients are released including phosphates (e.g. phosphatases) and sulfates (e.g. sulfatases), or monomer carbohydrates as energy sources by soil organisms''e.g. '-glucosidase or '-glucosaminidase). These EAs are measured in air-dried soil with appropriate substrates under similar assays in regards to buffers pH, incubation time and colorimetric determination facilitating comparisons due to management across soils. Although the assays are similar, the current protocol is to measure each EA independently and a biogeochemical cycling index calculated from the individual EA values. However, the burgeoning interest in soil health has created a need for high-throughput (and simple) assays that are more cost effective compared to measuring multiple enzymes independently. Therefore, to simplify enzyme assays, we evaluated two to three EAs in the same soil sample according to the following combined assays: 1) ß-glucosidase and acid phosphomonoesterase (C and P cycling index), 2) ß-glucosaminidase and arylsulfatase (C, N and S cycling index), 3) ß-glucosidase and ß-glucosaminidase (C and N cycling index), and 4) ß-glucosidase, acid phosphomonoesterase and ß-glucosaminidase (biogeochemical potential index). For each combined assay, the measured EAs obtained when incubating more substrates in a soil sample showed significant correlations (P<0.001) with the sum of the EAs calculated from the individual assays (theoretical EAs). The combined EAs showed also positive significant correlations (P<0.001) with soil organic C. We provide four options for developing biogeochemical potential indexes derived from assaying multiple enzymes simultaneously. This approach can reduce the time, resources and wastes generated from the assay of these four enzyme activities individually.