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Dissertation/Thesis Abstract

Effects of Sustainable Fertilizers on Yield and Nutritional Quality of Brassica rapa var Bonsai Chinensis, Hibiscus sabdariffa L., and Amaranthus Viridis L. Grown on the Delmarva Peninsula
by Burton, Nadine M., Ph.D., University of Maryland Eastern Shore, 2017, 189; 27545780
Abstract (Summary)

Demographics on the Delmarva Peninsula are becoming more diverse, resulting in more demands for ethnic crops; hence, there are opportunities for small farmers to diversify crop offerings and capitalize on this trend. The goal of this project was to identify sustainable production practice(s) that can produce high yielding and highly nutritious ethnic crops in the local environment and simultaneously improve soil health and soil mineral contents. Therefore, the yield and micronutrient contents of selected ethnic crops, such as Hibiscus sabdariffa L., Amaranth viridis Linn, and Brassica rapa cv. Bonsai, and soil fertility were examined as affected by three sustainable production practices, namely green manure, organic fertilizers, and biofertilizers.

During the 2016 growing season, four field studies were conducted at 3 separate locations on the University of Maryland Eastern Shore research farm to examine yield, phytonutrients, and essential trace elements of 2 varieties of Brassica rapa cv. Bosai Chinensis (Bok choy; Mei Qing Choi hybrid and Joi Choi hybrid), Amaranthus viridis L. (amaranth), and Hibiscus sabdariffa L. (hibiscus) and changes in soil properties after their production, using bio- and/or sustainable fertilizers. The bok choy varieties were subjected to six treatments ((1) Control (chemical fertilizer, 20:20:20), (2) Vermicompost Tea and Fish Emulsion (VCT+FE), (3) Poultry Litter Leachate (PLL), (4) Control + Azospirillum (Azo), (5) VCT+FE+Azo, and (6) PLL+Azo) in a randomized complete block design. In another study, the bok choy was treated with cowpea green manure. Amaranth and hibiscus were grown under three treatments ((1) Control, (2) VCT + FE, and (3) PLL).

Bok choy plants were harvested at the mature stage. Amaranth stems were harvested in 3 weeks after planting and every week thereafter for 13 weeks. Mature hibiscus calyces were harvested four months after planting. Parameters measured were yield, phenolic contents, antioxidant activities, essential trace elements (Cr, Fe, Mn, Co, Ni, Cu, Zn, and Se), and mineral content and soil biological activities. The data for phenolic contents, essential trace elements, and antioxidant activities for amaranth harvested weekly were analyzed using “proc mixed” procedure. The rest of the data were analyzed by two-way analysis of variance (ANOVA). Least square means (lsmeans) were calculated to estimate means and standard errors and they were compared using “pdiff”.

Results showed that the yields for all three crops treated with sustainable fertilizers were not different from Control (chemical fertilizer). The yields of bok choy and hibiscus calyces grown in different locations with different soil properties were significantly different (P < 0.05), but those of amaranth leaves were not. The yield of amaranth leaves was affected by harvest time. The weekly yields of amaranth leaves between Weeks 3 and 9 (1.46–2.34 kg/m2) were significantly higher than those at Weeks 1, 2, 12, and 13 (0.25–1.09 kg/m2) (P > 0.05). The weekly harvest of amaranth could increase its total yield per area because this practice can stimulate the development and growth of new stems and delay flowering.

Phenolic and essential trace element contents and antioxidant capacities in bok choy varied depending on varieties, locations, and treatments, but overall the sustainable fertilizers did not affect the micronutrient contents and antioxidant capacities in bok choy compared to chemical fertilizer. Interestingly, Total phenolic content and antioxidant activities, including 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging capacity and oxygen radical absorbance capacity (ORAC) (5.37 mg gallic acid equivalents/g dry matter (DM), 4.40 mg Trolox equivalents (TE)/g DM, and 214.18 µmol TE/g DM, respectively), were significantly higher in Joi Choi bok choy plants treated with VCT+FE+Azo than plants (4.75, 3.90, and 180, respectively) treated with VCT+FE without Azo (P < 0.05), indicating the Azospirillum may stimulate the phenolic production. Contents of some of essential trace elements in Mei Qing bok choy varied depending on locations and fertilizers. Those in the bok choy treated with chemical fertilizer were similar to or higher than those with sustainable fertilizers. Overall the essential mineral contents in bok choy were not much affected by locations and fertilizers. In the hibiscus calyces, phenolic contents and antioxidant capacities were not affected by locations or fertilizers, but essential trace elements were significantly affected by locations probably due to their soil mineral contents. In the amaranth leaves, phenolic contents and antioxidant capacities were significantly affected by locations (P < 0.05), but not by fertilizers. Its essential mineral contents were not affected by locations or fertilizers, except for Cr and Zn whose contents (4.32 and 63.28 µg/g DM, respectively) were higher in VCT+FE-treated amaranth than in Control (2.75 and 55.47, respectively) (P < 0.05). Overall, phenolic and essential trace element contents and antioxidant capacities in the plants treated with chemical fertilizer were not different from those treated with sustainable fertilizers.

The application of cow pea green manure increased the soil biological activity by 41% and maintained the soil NO3 concentration after the bok choy production, while the application of Control did not affect the soil biological activity but drastically depleted soil NO3 by 83.7% after the production. The application of sustainable fertilizers (VCT+FE and PLL) significantly increased the soil biological activities by 37% and 30%, respectively, after amaranth production, compared to Control by 12% (P < 0.05). They also significantly increased the soil biological activity by 33% and 28%, respectively, after hibiscus production, compared to Control by 15%. The result indicated that sustainable fertilizers (cow pea green manure, VCT+FE and PLL) can improve soil biological activities after the plant production and, consequently, increase potential nitrogen release and carbon sequestration for the future production, which can sustain the ethnic crop production and increase the profitability.

In conclusion, the sustainable fertilizers (cow pea green manure, VCT+FE, and PLL) can be used as alternatives for chemical fertilizers to sustainably produce the ethnic crops, such as bok choy, amaranth, and hibiscus on the Delmarva, without soil depletion and adverse effects against the environment. These practices have potentials to diversify crop production to meet demands for eatery by the diverse populations and to produce value-added produce, and boost income of small farmers on Delmarva.

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Indexing (document details)
Advisor: Min, Byungrok R., Cotton, Corrie
Commitee: Shwarz, Jurgen G., Marsh, Lurline E., Nindo, Caleb
School: University of Maryland Eastern Shore
Department: Department of Education
School Location: United States -- Maryland
Source: DAI-B 81/6(E), Dissertation Abstracts International
Subjects: Agriculture, Food Science
Keywords: Amaranth, Brassica, Delmarva, Green manure, Hibiscus, Sustainable fertilizer
Publication Number: 27545780
ISBN: 9781392871652
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