Growth and Gas Exchange Responses of Maize and Banana Plants in an Intercrop with Agroforestry Tree Species in Vihiga County, Kenya

Abstract

Agroforestry trees have been reported to improve soil fertility through nitrogen fixation, coupled with leaves and twig decomposition. High human population pressure in Vihiga County has led to reduced land area under farming. This has resulted into increased demand for food and consequently forced smallholder farmers in the region to carry out poor farming practices such as continuous cultivation and clearing of trees to avail more land for crop production. The poor farming practices have occasioned severe land degradation, climate change and reduced farm productivity. However, it is not known how intercropping maize and banana with Sesbania sesban, Calliandra calothyrsus and Leucaena diversifolia impacts on the growth and gas exchange parameters of maize and banana. The objective of this study was to determine the effect of intercropping agroforestry tree species with maize and banana on maize and banana height, leaf area, number of leaves, stem diameter, intercellular Carbon (IV) oxide concentration, transpiration rate and net photosynthesis in Vihiga County. The study was conducted at Maseno university farm located in Vihiga County in Kenya. The Williams varieties of banana of the same age were obtained from KALRO-Thika. Seeds of selected agroforestry trees were obtained from KEFRI – Muguga, planted in a seedbed and the seedlings raised in nurseries before being transplanted in the study plots. Hybrid maize seed (H513) was purchased from an agrovet. Banana holes were dug 2x2 feet, 20 Kg of decomposed cow dung manure + 20 Kg of top soil + 200g of NPK fertilizer added in each banana hole before planting. A Randomized Complete Block Design (RCBD) with 3 replications was used with seven treatment levels of unfertilized Maize (M), Banana (B), Maize + Banana + Calliandra (MBC), Maize+ Banana+ Leucaena (MBL), Maize+ Banana+ Sesbania (MBS), Maize + Banana (MB) and Fertilized Maize (MF). Maize was planted at 0.75 m inter row by 0.3 m spacing. Fifteen (15) tagged maize and four (4) banana plants in each plot were sampled for measurement of height, number of green leaves, leaf area, stem diameter, intercellular Carbon (IV) oxide concentration, transpiration rate and net photosynthetic rate. The data was subjected to Analysis of Variance using Genstat statistical package version 15.2. Means were separated using Fischers’ protected LSD test at 95% confidence level. The MBS treatment showed higher growth in terms of height, leaf area, number of leaves and stem diameter throughout the study period. Increased growth seen under fertilized maize was not significantly different from those under MBS. Gas exchange responses had no significant differences (p≤0.05) among most treatments. However, agroforestry tree species had shown higher intercellular Carbon (IV) oxide concentration, transpiration rates and net photosynthesis of maize and banana plants. Sesbania sesban reported maximum intercellular Carbon (IV) oxide concentration, transpiration rates and net photosynthesis as compared to those treatments without agroforestry trees. Therefore, incorporating nitrogen-fixing trees in farming could have a positive impact on growth, increased carbon (IV) oxide intake, transpiration rates and net photosynthetic rate. Sesbania sesban promoted growth and recorded higher gas exchange parameters of maize and banana. These findings may be used to advice smallholder farmers of Vihiga County on the best intercropping system and agroforestry tree species to adopt for maximum maize and banana yield.