Effect Of Organic And Inorganic Fertilizers On Growth, Yield And Quality Of Amaranths In Kiambu County, Kenya

ABSTRACT

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.