Zoe Heuermann

Date of Award

2018

Document Type

Thesis

Degree Name

Bachelors

Department

Natural Sciences

First Advisor

Clore, Amy

Area of Concentration

Biology

Abstract

The biological compounds in the soil that are integral to the cycling of nutrients and management of other soil properties are collectively known as soil organic matter (SOM). Cover crops, plants grown in addition to the primary cash crops to help maintain the agroecosystem, have been reported to build up SOM under some conditions. The purpose of this study was to determine the effects of cover crops in rotation with winter wheat and fallow on SOM fractions over three years at the Columbia Basin Agricultural Research Center near Pendleton, OR. In June 2017, soil was sampled from 30 plots randomly assigned one of the following cover crop treatments—pea, barley, mustard, a mixture of each or a fallow control. The cover crop treatments were not significantly different in terms of most SOM fraction concentrations, which may have been due to delayed effects and/or the noted suboptimal environmental conditions related to precipitation and soil pH. The plots sampled while in the wheat rotation phase had significantly greater levels of soil organic carbon, total nitrogen, particulate organic matter carbon, mineralizable carbon and microbial biomass carbon than the plots in the cover crop rotation phase at the time of sampling. These results were speculated to be in part of the added nitrogen fertilizer, which was only added to the plots in the wheat phase. However, these positive effects may be short-term in duration. Suggestions are given for future analyses, which will be necessary to make definitive conclusions about the effects of cover crops and wheat on SOM.

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