Agronomy and Horticulture, Department of


First Advisor

Martha Mamo

Second Advisor

Haishun Yang

Date of this Version



E. Hosseiniaghdam (2021), Quantifying the Combined Effect of Abiotic Factors on the Decomposition of Organic Matter in Semiarid Grassland Soils. PhD diss. University of Nebraska, Lincoln, NE


A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Agronomy and Horticulture (Soil Science), Under the Supervision of Professors Martha Mamo and Haishun Yang. Lincoln, Nebraska: August 2021

Copyright © 2021 Elnazsadat Hosseiniaghdam


Grassland ecosystems play a critical role in the global carbon cycle, and their cumulative carbon dioxide (CO2) emissions can be affected by animal grazing where litter (i.e., dead plant material) is trampled into the soil. However, the subsequent effects of trampling on litter decomposition are not well understood. Meanwhile, abiotic factors, especially temperature and soil moisture, are known to strongly affect litter decomposition. Due to the very small number of published studies that have considered litter placement, either litter on top of soil or litter mixed with soil as a factor in litter decomposition under different temperature and soil moisture conditions, reported results are contradictory; thus, conclusions cannot yet be drawn regarding how grazing management can best sustain and improve the soil fertility and productivity through litter deposition in semi-arid grassland system. We hypothesize that the effect of abiotic factors on litter decomposition shifts overtime during the growing season, and litter placement and its interaction with abiotic factors alter decomposition rate and the contribution of soil organic matter (SOM) and litter to total carbon (C) output and remaining C in soil.

It was found that under cool and dry (mimic early season) and warm and dry (mimic late season) conditions, litter decomposition is restricted. Decomposition was slower for the litter on top than the litter mixed into the soil. The frequency of dryingwetting cycles combined with temperature altered the respective proportions of the SOM and litter in the total carbon decomposition. Relationships among litter input, litter placement, and abiotic factors should be considered as upscaling factors in carbon decomposition models to improve modeling tools and land use strategies to sustain and improve soil organic matter content and thus the fertility of semiarid grasslands.

Advisors: Martha Mamo and Haishun Yang