Date

2018

Department or Program

Environmental Studies/Science

Primary Wellesley Thesis Advisor

Jaclyn Hatala Matthes

Additional Advisor(s)

Beth DeSombre

Additional Advisor

Kristina Jones

Abstract

Fertilizers provide nitrogen to agricultural crops, which is often the nutrient limiting plant growth. However, synthetic fertilizers are often not preferred or possible sources of soil nutrients due to economic and ecological reasons. Agroecological practices have historically incorporated legumes and mulching into agroecosystems to improve productivity. This research investigated the effects of legume mulching on small scale vegetable crop productivity. The experiment was conducted in the Wellesley College Edible Ecosystem Garden in 24 replicate barrel collars. In each barrel, I planted two spinach (Spinacia oleracea, variety ‘Tyee’) and two lettuce (Lactuca sativa, variety ‘Romaine’) plants. In half of the barrels, I incorporated the dried biomass of crown vetch (Securigera varia), a nitrogen-fixing plant, as a mulch, with the goal of adding nitrogen to the soil as a treatment group. I hypothesized that decreased nutrient deficiency would lead to increased plant productivity by increasing soil inorganic nitrogen content, increasing aboveground plant biomass and above to belowground biomass ratio, and increasing soil respiration rates in the treatment group. Inorganic nitrogen levels increased post-experiment in all barrels. They were higher in the treatment group soils post-experiment, significantly so for nitrate (NO3-). This supports the hypothesis that nutrient deficiency would decrease in the treatment group. The aboveground biomass, and subsequently the above to belowground biomass ratio, was lower in the treatment group. These results are likely due to preferential herbivory of treatment plants due to higher nutrients. The effects on ecosystem feedbacks, namely respiration, did not show significant differences between control and treatment groups, and so the null hypothesis could not be rejected. I conclude that while further research is needed, results support that crown vetch as a legume mulch increases increases soil nitrogen, and likely increases productivity.

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