MB and PL enhanced β-carotene in Amaranth compared with NPK but that of Celosia and Gboma was enhanced by MB and NPK fertilizer. Total phenolic content was higher among Amaranth plants receiving NPK, whereas those for Long Bean were greater among plants receiving MB or NPK fertilizer. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) activity was enhanced by MB, MB and NPK, or MB only among Amaranth, Celosia, Gboma, and Long Bean plants, respectively. These results suggest that the impact of organic amendments on biomass production was marginal and that species exerted a greater influence. However, there appears to be an enhancement of total phenolics and DPPH activity in response to organic amendments.
Vegetable Amaranth (Amaranthus hybridus) (Mosha et al., 1995), Celosia (Celosia argentea) (Orhue, 2010), Gboma (Solanum macrocarpon) (AVRDC, 2002), and Long Bean (Vigna unguiculata) (Chitindingu, 2005; Mosha et al., 1995; Palada et al., 2006), are highly nutritious niche market specialty vegetables being evaluated for growth, adaptability, and production under Alabama conditions, including responses to different organic fertilizers. Amaranth and Celosia are leafy vegetables that are good sources of antioxidants and phenolics, are similar to spinach, and are commonly grown in parts of Africa and Asia (Chitindingu, 2005). Gboma is widely grown in Africa and Southeast Asia for its fruits as well as its leaves, which are similar to those of kale and are good sources of protein, fiber, vitamins, and minerals (Schippers, 2000). Long Bean is popular in Asian countries, and its pods are similar to that of snap beans but are pencil thin and are harvested when immature before seed fill. Long beans have adequate levels of vitamin C, provitamin A, folate, and protein (Mosha et al., 1995).
Animal manures such as PL and hydrolyzed fish fertilizers are relatively less expensive than conventional inorganic fertilizers and readily available (especially PL). Manures are relatively good sources of plant nutrients and organic matter (Kpomblekou et al., 2002; Toor et al., 2006) and not only improve soil physical and chemical properties, but also enhance plant growth (Boyhan et al., 2010; Russo, 2010). For example, an incubation study evaluating nitrogen (N) availability from liquid fish protein-based organic fertilizers, Hartz (2010) showed that 79% to 83% of total N was available after 1 week and 83% to 99% after 4 weeks. In addition, PL and hydrolyzed fish fertilizers when used as organic amendments also increase disease and insect resistance, extended the shelf life of produce, and enhanced microbial activity (Davis and Riordan, 2004).
Russo (2010) evaluated the effects of the frequency of applied PL compared with an annual application of NPK on the production of bell peppers (Capsicum annuum), sweet corn (Zea mays), and cucumbers (Cucumis sativus). He found that an annual treatment with PL produced higher marketable yields of bell pepper and sweet corn compared with application in alternate years, whereas the opposite was true for cucumber.
Boyhan et al. (2010) reported that PL applications increased total yield of short-day onions but reduced that of medium bulbs. AdeOluwa and Cofie (2011) reported that vegetable Amaranth plants had a positive response to organic compost but the response varied with time and environmental conditions, whereas Jaipaul et al. (2010) reported that organic manures increased plant height of pepper and garden pea. Masarirambi et al. (2012) evaluated the effects of poultry manure applied at 20, 40, and 60 t·ha−1 on lettuce production in South Africa and reported greater total and marketable yields at the 60-t·ha−1 rate.
Plant responses to hydrolyzed fish fertilizers appear to be species-dependent. Schupp et al. (1993) reported that fish hydrolysate fertilizer reduced fruit set of ‘Delicious’ and ‘Golden Delicious’ apples. In contrast, Smagula and Dunham (1995) showed that fish hydrolysate fertilizer was as effective as 5N–10P–5K in raising leaf N, P, and K concentrations in prune and crop-year leaf samples as well as stem length and yield of low bush blueberry; fish hydrolysate is an acceptable alternative to soluble fertilizer for cranberries (DeMoranville, 1990).
Fruits and vegetables are critical parts of a healthy diet and are rich sources of many nutrients such as vitamins C and K, folate, thiamine, carotenes, several minerals, and dietary fiber (Palada et al., 2006). In addition, antioxidants that occur naturally in these fruits, vegetables, and whole grains are powerful weapons in combating inflammation and lowering heart disease and cancer risk (Odukoya et al., 2007).
Studies on organically grown produce have shown differences in micronutrient and phytochemical content, sometimes as high as 30% in contrast to crops conventionally grown (Riordan and Davis, 2005). Weibel (2000) harvested apples from five pairs of organic/integrated fruit farms with similar microclimate, soil conditions, and planting system and reported that contents of phenols (mainly flavonols) were 19% higher in organically grown apples, In contrast, Toor et al. (2006) reported that lycopene levels in tomato were reduced by the application of organic amendments. Zhao et al. (2007) reported that the levels of phenolic compounds in lettuce were consistently impacted by the nutrient source and suggested that this could have been related to general factors including the environment, season, and cultivar differences. Additionally, peppers and garden peas fertilized with organic manure have been previously shown to have higher vitamin C, total phenolics, and anthocyanin content (Abu-Zahra, 2011; Jaipaul et al., 2010). Similarly, broccoli treated with organic and bio-organic fertilizers produced antioxidants with greater chelating power (El-Moniem et al., 2012).
Although improved yield responses and higher phenolic concentrations have been reported in organically grown crops, these reports are generally inconsistent, because other factors may be involved (Carbonaro et al., 2002; Lombardi-Boccia et al., 2004; Sousa et al., 2005). For example, Young et al. (2005) suggested that organic systems may expose leafy vegetables to attack by insects resulting in higher concentrations of phenolics as plants produce them as a part of their defense mechanism.
Our objective was to evaluate the influence of a hydrolyzed organic fish fertilizer and PL on biomass production, total phenolic, and antioxidant content and DPPH activity of Amaranth, Celosia, Gboma, and Long Bean.
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