Effects of leaf extracts, organic, inorganic fertilizers on soil ph, growth, soil macronutrients, beta-carotene of amaranthus in Kiambu County, Kenya

Abstract

Soil is a significant reservoir for plant nutrients and hence necessary for plant growth. Soil pH is a very important chemical property of the soil, as it dictates the availability of plant nutrients. Low soil pH reduces soil nutrients. Some of the factors leading to acid soils include continuous cultivation of soil due to scarcity of arable land, excessive use of inorganic fertilizers, climate change and deforestation. Reclamation of acidic soils includes addition of lime which is expensive and requires re-application. These do not add all the nutrients required by plants and may also contain soil contaminants which can make the soil unproductive or may result in contaminated products harmful to humans if consumed. Some plant leaves and their extracts reduce soil acidity and add plant nutrients to soils as well as improving soil texture. The objective of this study was to evaluate the effects of leaf extracts from selected trees on soil acidity, their effect on soil macro nutrients, growth and betacarotene levels of amaranthus. Plant leaves that were tested were Turril (Vitex keniensis), Mexican sunflower (Tithonia diversifolia) and Indian nettle (Plectranthus barbatus).Amaranthus (Amaranthus spp.) leaves are a good source of vitamin A, vitamin C, and folate and were therefore used as a test crop. The experiment setup was in a randomized complete block design (RCBD) with three replicates, arranged in a two by seven factorial with two species of amaranthus.The soil treatments were the three leaves extracts, lime, farm yard manure, inorganic fertilizer and control. Data on plant height, leaf area, number of leaves, fresh weight and dry weight and levels of beta carotene were collected from the amaranthus grown on the treated soil.AOAC method was used for analysis of beta carotene. All data was subjected to analysis variance (ANOVA) at 5% level of significance using SAS and least significant difference (LSD) for means separation,every week for four weeks.The results showed that leaf extracts,Plectranthus barbatus reduced soil acidity(pH5.9) to (pH6.7),while inorganic fertilizer increased the acidity (pH5.9)to (5.3).On the growth parameters ,FYM (47.0g) and leaf extract Vitex keniesis(45.17g) gave the highest increase while control(26.3g) the least. On the macronutrients analysis in the soil,F.Y.M(0.244%) gave the highest nitrogen levels while control gave the least (0.138%), on phosphorus inorganic fertilizer(32.75ppm) and F.Y.M.(32.42 ppm) gave the highest levels while lime(25.08ppm)the least and on potassium, leaf extract Plectranthus barbatus(1.416me/100g)gave highest levels and control(1.311me/100g) the least. Betacarotene levels,F.Y.M(51.1μg) and leaf extract Plectranthus barbatus(46.1μg)gave the highest betacarotene levels while control the least(19.22μg).Amaranthus with high levels of betacarotene, have an antioxidant which fights cancer cells.The outcome, of the research will be used in recommendation of economical organic fertilizer leading to decreased dependence on inorganic fertilizer especially for small scale farmers with 0.4 ha and below within Juja Ward in Kiambu County,Kenya.