Browsing by Author "Kenyanya, Omanga"

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    Determination of Potassium Levels in Intensive Subsistence Agricultural Soils in Nyamira County, Kenya
    (2013) Kenyanya, Omanga; Wachira, Jackson M.; Mbuvi, Harun
    Assessment of potassium levels in agricultural soils of Nyamira County, Kenya was necessitated by the observed progressive drops in maize acreage yields over the years despite use of phosphorus and nitrogenous fertilizers. In the study, concentration levels of potassium and other soil fertility indices such as, organic carbon, cation exchange capacity, exchangeable cations, soil pH, available nitrogen, total and available phosphorus were determined. Five composite soil samples were collected at depths of between 0-30 cm from five farms that have consistently been under intensive cultivation. Fractionation of potassium was achieved by sequential extraction of soil sampleswith distilled water, ammonium acetate and nitric acid in that order. Concentration levels of potassium in the extracts were determined using a flame photometer. Potassium concentration levels obtained from the water soluble soil extracts were used to calculate thermodynamic parameters such as free energy of replacement, potassium activity ratio and ionic strength of the soil solution. The relationship between the adsorbed and equilibrium potassium concentration, quantity/intensity was determined by plotting Freundlich adsorption isotherms. The isotherm was used to determine the buffering capacity ofpotassium and the concentration levels of potassium adsorbed on un-specific sites in the soil. The suitability of the adsorption equation was determined by applying the least square regression analysis. From the study available potassium in the soils ranged from 57 to 70 mg/kg and had amean value of 60±5.54.2 mg/kg (ammonium acetate method). The water soluble potassium ranged from 1.8 to 2.2 mg/kg with a mean of 2.02±0.16 mg/kg. Nitric acid extracted potassium had a mean of 149.±2.306 mg/kg. The mean free energy of replacement, Δ𝐹𝐹, was found to be −3572±44.98 cal/mol indicating that the soils have low supplying power of potassium. The potassium buffering capacity of the soils was found to have a mean of 1.189±0.06 mg/kg. The amount of potassium adsorbed on un-specific sites of the soilshad a mean value of 6.993±2.378 L/kg. These findingsreveal the extent of potassium depletionin the soils of this region and will form a baseline for working acreage potassium doses required for remediation.
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    Studies on Potassium requirements for maize in Nyamira County, Kenya
    (2015-03) Muthengia, Jackson M.; Kenyanya, Omanga
    In Kenya, Maize is a key cereal crop and a major staple food in most Kenyan families. Most maize farmers mainly apply nitrogenious and phosphorous fertilizers to improve on maize yields in the country and Nyamira county in particular. However, acreage yields have been declining yearly despite their use. Application of potassium (K) fertilizers in the regionis limited yet it is the third major nutrient required by maize crop in large quantities for optimum growth and yields. Consequently, it is no longer wise to assume that the soils in the region have enough K levels for good growth and yields. The present study was planned to determine the soils nutrient status and evaluate whether K fertilizers use can play a role to improve maize yield in the region. The field experiments were set and conducted in Gachuba location in Nyamira county. Equilibria K concentrations were determined by flame photometry from filtrate of 2.5g soil in 25ml solutions of various potassium concentrations (0, 25, 50, 75, 100, 125, 150, 175, 200, 225 and 250 mgL-1) after string the mixtures for 24 hours to achieve steady state condition. Adsorption data obtained from the various soil solutions of K were fitted into Langmuir, Freundlich, Temkin and Van Hauy equations. The data fitted Best in Freundlich isotherm model and were farther used to calculate acreage doses. Maize was grown under same doses of nitrogenous and phosphorus fertilizer and ten different doses of potassium in plots of 6m by 5m at two farm sites , that is Gachuba (farm site 1) and Kiang’ede (farm site 2). Maize performance with site and dosage aaplication were determined and growth parameters as well as yield parameters recorded. The study found that maize growth parameters of plant height and stem girth and its yield parameters of ear weight, ear length and grain yields increased steadily as potassium doses were increased and reached their optimum values at potassium doses of 155.84 and 144.76 kg ha-1 giving yields of 3315.27kg ha-1 and 3340.50 kg ha-1 for farm sites 1 and 2 respectively. The concentration levels of available potassium in the soils ranged from 57 to 70 mg kg-1 and with a mean value of 60+- 5.542 mg kg-1. The water soluble potassium ranged from 1.8 to 2.2 mg kg-1 and gave mean of 2.02+-0.16 mg kg-1. Nitric acid extracted potassium had a mean of 149+-2.306 mg kg-1. The mean value energy of replacement, was found as -3572+- 44.98 cal mol-1. The study indicated insufficiency of potassium in the soil for optimum maize production in the region. Also, it established that potassium doses significantly affected concentrations of Phosphorus and nitrogen in the tissues. The findings of this research will create awareness the extent to which potassium has been depleted in soils in the region to both farmers and policy makers and hence appropriate action taken. Also, the information is expected to help extension officers and Farmers to use correct K doses for optimum yields.