Enzyme activities distinguish long-term fertilizer effects under different soil storage methods

Authors: Reardon, Catherine - Kate; KLEIN, ANN - Former ARS Employee; MELLE, CAROLNE - Former ARS Employee; HAGERTY, CHRISTINA - Oregon State University; Klarer, Emmi; MACHADO, STEPHEN - Oregon State University; PAULITZ, TIMOTHY - US Department Of Agriculture (USDA); PRITCHETT, LARRY - Oregon State University; SCHLATTER, DANIEL - US Department Of Agriculture (USDA); Wuest, Stewart

Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2022
Publication Date: 5/11/2022
Citation: Reardon, C.L., Klein, A.M., Melle, C.J., Hagerty, C.H., Klarer, E.R., Machado, S., Paulitz, T.C., Pritchett, L., Schlatter, D.C., Wuest, S.B. 2022. Enzyme activities distinguish long-term fertilizer effects under different soil storage methods. Applied Soil Ecology. 177. Article 104518. https://doi.org/10.1016/j.apsoil.2022.104518.
DOI: https://doi.org/10.1016/j.apsoil.2022.104518

Interpretive Summary: Long-term fertilization with inorganic nitrogen (N) or manure has significant impacts on the soil quality and the microbial communities driving the supply of nutrients to the soil. Understanding the complex interactions between the soil communities, management practices and the soil environment is an important step toward improving soil health. The Long-Term Experiments in Pendleton, OR, USA were established as early as 1931 to evaluate the impacts of crop management (i.e. tillage, crop rotation, fertility, residue treatment, frequency of fallowing) on dryland wheat production under intermediate annual precipitation (~16 inches annual precipitation). In this study, we evaluated the Crop Residue Trial of the Long-Term Experiments in Pendleton to determine the impact of different fertilizer treatments (no fertilizer, inorganic fertilizer applied as urea ammonium-nitrate, or organic fertilizer applied as steer manure) on soil enzymes involved in the decomposition of organic matter and nutrient supply to soil. We analyzed enzymes involved in the release of carbon (ß-glucosidase, glucosaminidase), phosphorous (acid and alkaline phosphatase), nitrogen (glucosaminidase, arylamidase), and sulfur (sulfatase) from organic matter. Additionally, we assessed the potential ammonia oxidation activity of soil which is an essential step in nitrification that impacts the availability and fate of inorganic nitrogen. Application of inorganic fertilizer acidified the soil whereas manure addition increased the pH and soil C content as compared to the no fertilizer control. The nutrient cycling activity of the soil enzymes was enhanced by the addition of manure compared to the application of either no fertilizer or inorganic fertilizer. The activity of the soil enzymes and ammonia oxidation were related to the soil chemical properties of total C, N, S, and pH. Soil enzyme analyses are recommended only for moist or air-dried soils, yet the archival methods of the Long-Term Experiments are either oven drying soils at 40°C (104°F) or air-drying in a greenhouse in which midday temperatures can reach up to 60°C (140°F). We determined that oven-dried soils could be used to assess trends in soil enzyme activity similar to moist soils for this site, although drying and storage greatly reduced the amount of activity. Overall, the addition of manure halted soil acidification and slowed carbon loss and increased nutrient cycling enzyme activity compared to unfertilized soil in the wheat-fallow system.

Technical Abstract: Long-term nitrogen fertilization imparts significant effects on the soil environment and soil microbial communities relevant to nutrient cycling. Understanding the complex interactions between soil biology, management practices, and the soil environment is an important step toward improving soil health. The Crop Residue study of the Long-Term Plots at Pendleton, Oregon USA demonstrate declines in soil quality with acidification and reduced soil carbon under a wheat-fallow cropping system. Soil enzyme activity (ß-glucosidase, ß-glucosaminidase, acid and alkaline phosphatase, arylsulfatase, and arylamidase) and ammonia oxidation was measured in plots managed with three different fertilizer treatments (no fertilization, urea-ammonium nitrate, and manure) at two stages of crop growth. The fertilizer treatments had a strong impact on total carbon and nitrogen and produced a broad range of soil pH from 4.8 (urea-ammonium nitrate) to 5.7 (no fertilizer) and 6.7 (manure). Overall, potential nutrient cycling activity (hydrolytic enzymes and ammonia oxidation) was enhanced in manure-fertilized soils except for acid phosphatase which was greater in the low pH soil. Treatment trends in the proportional geometric mean (an index of soil nutrient cycling capacity) were generally consistent over a 32-year transect excluding acid phosphatase. All activities were highly correlated to total carbon, nitrogen, and sulfur. Except for ß-glucosaminidase, all enzymes were also highly correlated to pH. The only enzyme to vary by crop phase was ß-glucosidase which was greater at boot than tillering. Soils remaining after the analyses were oven-dried at 40'°C and stored in a non-climate-controlled warehouse for archiving. After 2-years of storage, the oven-dried soils were re-assessed for hydrolytic enzyme activity to determine whether the ability to distinguish treatment differences is retained in archived soils. The oven-dried archived samples showed similar contrasts as the soils analyzed moist between manure and the other fertilizer treatments, although the level of activity was significantly reduced. Overall, long-term fertilization with manure slowed the decline in soil acidity and enhanced soil function relevant to nutrient cycling and organic matter dynamics in the wheat-fallow cropping system.Long-term nitrogen fertilization imparts significant effects on the soil environment and soil microbial communities relevant to nutrient cycling. Understanding the complex interactions between soil biology, management practices, and the soil environment is an important step toward improving soil health. The Crop Residue study of the Long-Term Plots at Pendleton, Oregon USA demonstrate declines in soil quality with acidification and reduced soil carbon under a wheat-fallow cropping system. Soil enzyme activity (ß-glucosidase, ß-glucosaminidase, acid and alkaline phosphatase, arylsulfatase, and arylamidase) and ammonia oxidation was measured in plots managed with three different fertilizer treatments (no fertilization, urea-ammonium nitrate, and manure) at two stages of crop growth. The fertilizer treatments had a strong impact on total carbon and nitrogen and produced a broad range of soil pH from 4.8 (urea-ammonium nitrate) to 5.7 (no fertilizer) and 6.7 (manure). Overall, potential nutrient cycling activity (hydrolytic enzymes and ammonia oxidation) was enhanced in manure-fertilized soils except for acid phosphatase which was greater in the low pH soil. Treatment trends in the proportional geometric mean (an index of soil nutrient cycling capacity) were generally consistent over a 32-year transect excluding acid phosphatase. All activities were highly correlated to total carbon, nitrogen, and sulfur. Except for ß-glucosaminidase, all enzymes were also highly correlated to pH. The only enzyme to vary by crop phase was ß-glucosidase which was greater at boot t