Mineral levels of some plants and their leaf extracts and their effects on soil pH and growth rate of selected non-leunious plants
Mwangi, James Njogu
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Essential plant nutrients are necessary for plant growth, However, some of these nutrients are added as inorganic fertilizers due to high demand of food arising from fast growth in population which has necessitated the need to expand agricultural activities. This has lead to overuse of commercial inorganic fertilizers leading to drop in soil pH. Low pH reduces the availability of essential nutrients to plants and also low rate of decomposition of organic matter that is required to increase buffering capacity of the soil. Soil acidity is reduced by liming, which is an expensive exercise and does not add fertility to the soil. Leaves and leaf extracts of different plants have been suggested as an alternative to inorganic fertilizer and liming materials. However their efficacy has not been tested. The study, therefore, aimed at investigating the effect of growth rate of non-leguminous plants, including wheat (Triticum aestivum), kale (Brassica oleraceae var acephala) and coriander (Coriandrum sativum L)., grown on acidic soils treated with leaves and leaf extracts of plants known to have high buffering capacity and mineralisation. The leaves and leaf extracts for this study were applied to the soil with low pH of 4.75. Leaves and leaf extracts were mixed depending on levels of macro-nutrients and mineralization of selected plants found in Nyandarua County. The growth rates of wheat (Triticum aestivum), kale (Brassica oleraceae var acephala) and corriander (Coriandrum sativum L) was monitored by comparing the dry mass of the uprooted seedlings from the experiment and control experiments for every fourteen days for a period 60 days. Determination of macronutrients in leaf extracts was done using flame photometry, atomic absorption spectrometry (AAS), UV/visible spectrometry and turbidmetry. Data analysis was done using analysis of variance (ANOV A) and student-newman-keuls (SNK) test. The mean pH value of leaf extracts ranged from 4.58±0.27a to 7A4±O.04d for 60 days. The highest mean levels in leaves (ug/g) K+; 189.95±O.l7c; Ca2+, 367.33±O.67e; Mi+, 114.33e±O.33; pol, 55.38±O.23f; N03-, 322.25±OAOf; and SO/-, 56A8±O.23e. There was significant difference in levels of macronutrient in soil treated with leaves and leaf extract (Le), commercial fertilizers (Ct) and untreated soil (Us). The mean growth rate for wheat (dry mass) was 1.27±O.13b g/wk (Le), 1.26±O.l2b g/wk (Ct) and 0.32±O.02a g/wk(Us) while in (height) was 7.29±1.43bcm/wk (Le) 6.20±1.95bcm/wk (Ct) 3.98±0.97acm/wk (Us). For kales 0.20±O.01a g/wk (Le), 0.30±O.02a g/wk and (Cf), and 0.03±O.01 b g/k (Us) while in (height) 2.l5±O.85c cm/wk (Le), 2.57±O.88b cm/wk (Ct) and 1.04±O.028 cm/wk (Us). The mean growth rate for corianders was O.l6±0.01a g/wk (Le), O.l7±O.02a g/wk (Cf), and O.lO±O.Ol a g/k (Us) while in (height) 1.85±O.56bcmlwk (Le), 1.86±O.58bcm/wk (Ct) and 0.79±O.l8a cm/wk (Us). Soil treated with leaves and leaf extract (Le), soil treated with commercial fertilizers (Ct) and untreated soil (Us), respectively. Mean values with the same small letters are not significantly different (p >0.05 SNK test). It was established that there was no significant difference in the growth rate of both wheat and kales grown on soil with commercial fertilizers (Cf), and Le. The results of this study indicate that leaves and leaf extracts of plants studied can be used as an alternative to inorganic fertilizers and should be recommended for agro-forestry in unproductive areas with low pH.