Assessment of Acacia nilotica in nitrogen fixation and nitrogen availability in the lake victoria basin: A case study at Kendu bay, Rachuonyo district of western Kenya

Abstract

Many soils of sub-Saharan Africa are severely nitrogen deficient but inorganic fertilizers are unaffordable for most subsistence farmers. Rotations and/or intercrop of trees (Acacias) with crops may alleviate nitrogen deficiency through biological N2 fixation and redistribution of subsoil nitrogen to the surface since Acacia species are known to be nitrogen fixing. The objective of this study is to evaluate the effectiveness of Acacia nilotica, Acacia senegal and Acacia xanthophloea to improve degraded lands by fixing nitrogen from the air, extract water and nutrient from deep down in the soil. A comparison will be done on their abilities to conserve moisture in their foliage and effects on Maize (zea mays L.) yields. The study will be carried out at Kendu Bay, Rachuonyo District of Western Kenya using completely randomized block design, transplanted Acacia seedlings of 4m by 4m, 3m by 3m and 2m by 2m spacing. Maize leaves will be sampled two times per season while soil sampling will be carried out four times a year at 0- 15cm depth to check on the amount of N fixation IN availability resulting from the trees. Maize (zea mays L.) will be planted in rows between the trees and on control plots twice a year. Soil will be analysed for total N, total P and pH determined. The maize yields will be compared against the control to determine the possible variation due to intercropping. Soil pH in water will be determined using a soil to water ratio of 1:2.5 while analysis of total N and P will be done using wet ashing. Wet acid oxidation will be based on Kjeldahl oxidation agent leaving acid solution. Hydrogen peroxide will be added as additional oxidising agent, selenium as a catalyst while lithium sulphate will be added to raise the boiling point of the mixture. The main advantages of this method are that single digestion will be required (for either soil or plant) to bring nearly all the nutrients into solution; no volatilization of metals, N and P takes place and the method is simple and rapid. The amount of total N and P will be determined colorimetric ally from the resulting solution. Data obtained will be analysed using Excel and ANOVA series. This study will help smallholder farmers in Sub-Saharan Africa and many other countries in the tropics (Kenya included) to overcome the problem of declining soil fertility resulting from continuous cropping without replenishing soil nutrients thereby improving the peoples livelihood and food security.