Effect of organic and inorganic fertilizers on growth, yield and quality of amaranths in Kiambu County, Kenya
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An experiment was carried out for two seasons in Kiambu County to investigate the influence of organic and inorganic fertilizer on growth, anti-nutrients characteristics in amaranth species and the changes in the soil rhizosphere. This is because continuous usage of inorganic fertilizer affects soil structure. Hence, organic manures can serve as alternative to mineral fertilizers. Application of pesticides and inorganic fertilizers had adverse effects on nutrient leaching, pesticide contamination, species extinction, and evolution of pesticide resistance. The experiment was 2×3×3 factorial arrangement in Randomized Complete Block Design (RCBD) with three replicates. The three factors were: two amaranth species (A. tricolar and A. cruentus); three NPK 17-17-17 rates (0, 250 kg/ha and 500 kg/ha); and three quail manure rates (0, 8.45 t/ha and 16.9 t/ha). The growth parameters assessed were root length, shoot length, leaf area and biomass of roots and shoot. Macro and micronutrients were also assessed in the plant tissue. The experiment was carried out for two seasons. Pre cropping soil analysis was carried out to assess soil pH, macro and micro-nutrients, analysis was also carried out after application of the fertilizers. Secondary metabolites (phenolics and oxalics) were determined in the two amaranth species. Soluble and total oxalates concentration and Phenolic concentrations were determined. Data was subjected to analyses of variance (ANOVA) at 95% confidence level using SAS computer software version 9.0 model TS1M2. The result showed that macronutrients increased except for phosphorous while the micronutrients and pH increased, nitrogen significantly p≤ 0.05 increased in the soil from 0.07% to 2.17%, potassium from 0.9% to 1.34%, the pH increased from 5.2 to 6.2, iron increased from 59.3 ppm to 167 ppm when 250 kg/ha of NPK + 8.45 t/ha of organic quail manure were used at 500 kg/ha +16.9 t/ha calcium increased from 1.7 to 3.93 me% in the second season and manganese from 0.16 me% to 2.61 me%. Sole NPK which is inorganic fertilizer slightly increased magnesium from 0.73 me% to 1.49 me% in the first season and to 1.52 me% in the second season, manganese was raised from 0.16 me% to 0.37 me% in the first season and to 0.46 me% in the second season. Oxalates and phenolic compounds significantly p≤0.05 increased with the highest recorded at the rate 16.9 t/ha of organic and 500 kg of inorganic fertilizer. The root length was highly significant at p≤0.01 in the first season but was lower at p≤0.05 in the second season. Root length reduced from 18.23 cm in season one to 12.86 cm in season two in A. cruentus when 16.9 t/ha of organic quail manure was applied at 16.9 t/ha+500 kg/ha in season one A. cruentus had 0.625 g of root dry weight which increased to 2.468 g but A. tricolor increased to 2.328 g from 0.72 g at the same application rate. There was no significant difference between the two varieties in absorption and assimilation of organic and inorganic fertilizer. Enhancement of macro and micronutrients can be linked to presence of cation exchange sites in the organic matter. Acidity also interfered with the microbial activities thus reducing the breakdown of organic matter because as the inorganic fertilizer rate increased the pH reduced. The results showed that a balanced use of organic manure and inorganic fertilizer at the rate of 250 kg/ha of NPK + 8.45 t/ha of quail manure should be applied to enhance macro and micronutrients and pH in the soil as well as the growth of amaranth.