Soil amendments yield persisting effects on the microbial communities--a 7-year study

Authors: Reardon, Catherine - Kate; Wuest, Stewart

Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/29/2015
Publication Date: 2/6/2016
Publication URL: https://handle.nal.usda.gov/10113/5265507
Citation: Reardon, C.L., Wuest, S.B. 2016. Soil amendments yield persisting effects on the microbial communities--a 7-year study. Applied Soil Ecology. 101:107-116. doi: 10.1016/j.apsoil.2015.12.013.

Interpretive Summary: Microbial communities are sensitive to soil amendments and largely control the break-down and accumulation of soil organic matter. In a previous study, soil amendment with 9 different carbon sources ranging from wood to sucrose resulted in different soil carbon to nitrogen ratios which lasted 7 years post-amendment in a Pacific dryland wheat-fallow crop rotation. The goal of this study was to determine whether the type of carbon amendment also imparted lasting effects on the microbial communities with detectable differences in activity, population size, or community structure. The microbial communities from the top 10 cm of soil were analyzed for activity related to nutrient cycling of carbon, nitrogen, phosphorous, and sulfur. The bacterial and fungal community size (amount) and structure (types present) were determined based on analysis of DNA extracted from the soil. The soil amendments were applied for 5 years under either annual wheat or continuous fallow. After the harvest of the final wheat crop following the last amendment, the ground was left fallow for approximately 3.5 years before returning to a wheat-fallow rotation. The soil amendments were added at similar carbon contents and included cotton linters, sucrose, wheat residue, composted wheat residue, Brassica residue, wood sawdust, alfalfa feed pellets, manure, biosolid and a no treatment control. Two crops, Brassica and grass, were included in the fallow treatments. Seven years after the final amendment, most treatments produced microbial communities that were similar to the communities of the no treatment control. Wood and sugar amendments and grass cropping produced the most pronounced effects on enzyme activity, fungal abundance and structure. Overall, crop type had the largest effect on soil enzyme activity and the amount of fungi, in which both were greatest under grass cropping compared to wheat or brassica. The fungal communities were sensitive to the carbon amendments, and the differences in the amount and types of fungi were observable 7 years after the amendments ended. No changes were observed in the bacterial community structure suggesting that either the bacteria were less sensitive to the amendments or the changes were not persistent. In summary, the microbial communities were differentially affected by C source amendments in which the persistence of change and the aspect of the community affected (i.e. function, size, structure, bacteria/fungi) were dependent on amendment type.

Technical Abstract: Soil microbial communities are sensitive to carbon amendments and largely control the decomposition and accumulation of soil organic matter. In this study, we evaluated whether the type of carbon amendment applied to wheat-cropped or fallow soil imparted lasting effects on the microbial community with detectable differences in either activity, population size, or community structure after a period of seven years post-amendment. The microbial communities from the top 10 cm of soil were analyzed for activity related to C-cycling (glucosidase, galactosidase), P-cycling (acid phosphatase), S-cycling (arylsulfatase), and N-cycling (ß-glucosaminidase, arylamidase) activity, in addition to fungal and bacterial abundance and diversity. The amendments were applied at similar carbon rates for five years under annual wheat or continuous fallow and included cotton linters, sucrose, wheat residue, composted wheat residue, Brassica residue, wood sawdust, alfalfa feed pellets, manure, biosolid and a no treatment control. Two crops, Brassica and grass, were in the fallow treatments. The majority of the communities recovered from the amended soils were not distinguishable from the no treatment control. Significant differences in the population size and community structure were observable for the fungal but not bacterial populations in response to different crops or amendments. Wood and sugar amendments and grass cropping had the most pronounced effects on enzyme activity, fungal abundance and structure. Overall, the crop species had a significant effect on the soil enzyme activity and population size of fungi, with the greatest values under grass compared to wheat or brassica. The bacterial and fungal communities were differentially affected by C source amendments in which the persistency of change and the aspect of the community affected (i.e. function, size, structure) were dependent on amendment type.