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Effects of Environmental Factors on Nutrients and Antinutrient Contents of Selected Leafy Vegetables
|Title:||Effects of Environmental Factors on Nutrients and Antinutrient Contents of Selected Leafy Vegetables|
|Abstract:||The purpose of this research was to test the hypothesis that plant composition in general, and plant antinutrient content in particular, are affected by environmental factors. To test this hypothesis three crops were grown in four benchmark locations which had been characterized for soils and provided with weather stations to monitor air and soil temperatures, relative humidity, rainfall, solar radiation and wind speed. The four experimental sites represented four soil series and two soil families. The Wahiawa and Lahaina soil series identified on sites on the Islands of Oahu and Molokai were members of the clayey, kaolinitic, isohyperthermic family of Tropeptic Eutrustox, whereas, the Niulii and Kukaiau soil series identified on sites in the Kohala and Hamakua districts of the Big Island of Hawaii were members of the thixotropic, isothermic family of Hydric Dystrandepts.|
Three test crops were used to test the hypothesis: amaranth (Amaranthus gangeticus L.), a crop cultivated for its tender leaves or grain, cassava (Manihot esculenta L.), a crop normally cultivated for its starchy tubers, and taro (Colocasia esculenta L. (Schott.), a crop normally grown for its underground corms. The leaves of all three crops are consumed by people in the warm tropics. For this reason, the leaves of all three crops were sampled and analyzed to measure the effects of soil and climate variables on oxalate, nitrate, and ionic contents of leaves.
Amaranth experiments were installed at three sites. At each site, irrigated and non-irrigated experiments were conducted. Within each irrigation experiment, three fertilizer treatments consisting of (1) a basal treatment of lime, N, P, K, bases, and trace nutrients, (2) a N treatment superimposed on the basal treatment, and (3) a P treatment superimposed on the basal treatment, were arranged in a randomized complete block design with three replications. Plant tops were harvested at maturity for chemical analyses.
Cassava leaves were sampled from ongoing experiments at the four experimental sites. Taro leaves were also sampled from ongoing experiments but from only three sites.
Soil and climatic factors significantly influenced the chemical compositions of crops. These effects differed for each crop. Nitrogen plays an important role in controlling the synthesis of oxalate and the accumulation of nitrate in amaranth. The highly variable oxalate and nitrate contents in plants grown in environmentally different sites were, to a large extent, due to different soil N contents.
Virtually all oxalate in cassava was in the form of calcium oxalate, so that tissue Ca content was an important factor in oxalate formation.
In taro, K appeared to be the key factor accounting for the difference in oxalate content among sites.
It was concluded from the results of this study that plant compositions can be controlled by management of the environment and crop selection. It follows from this conclusion that the nutritional quality of food crops can be measurably improved if more research is directed towards achieving this goal.
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Ph.D. - Agronomy and Soil Science|
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