IMPACT OF TILLAGE AND FERTILIZER REGIME ON SOIL NITRFYING BACTERIA AND ARBUSCULAR MYCORRHIZAL FUNGI ACTIVITIES UNDER CASSAVA (Manihot esculenta L.) CULTIVATION

Abstract

ABSTRACT

Farmers in south-west Nigeria are willing to adopt practices such as tillage and fertilizer to increase cassava root yield. Meanwhile, the adoption of these agronomic practices has implications for microorganisms that are related to both soil and cassava nutrition. A study was therefore carried out to determine the effect of tillage and fertilizer application on arbuscular mycorrhizal fungi (AMF) and nitrifying bacteria populations in cassava cultivation. Additionally, the uptake of nitrogen (N), phosphorus (P) and potassium (K) in cassava and their concentration in the soil were monitored. The study was carried out in 2016 and 2017 on two farmers' fields each at Ido, and Odeda Local Government Areas in Oyo and Ogun state respectively. The experiment comprised two levels of plough till {single plough (SP) and zero plough (ZP)}, two levels of traditional ploughing {ridge (R) and flat (FL)} and fertilizer application {fertilized (F) and unfertilized (F1)} arranged in a split-split plot fitted in a Randomized Complete Block Design with three replicates. Cassava variety TME 419 was planted at 1 m × 0.8 m spacing. Spores population and AMF species associated with cassava were isolated and identified. Per cent root colonization (RC) was determined by the grid-plate method while Nitrosomonas and Nitrobacter were cultured on Winograsky selective media and colonies counted were expressed in colony-forming unit (CFU). N, P, and K uptake and root yield were determined at harvest. Data collected were subjected to Analyses of Variance using R statistics software version 3.6.2 for Windows and treatments means were separated using the Least Significant Difference at p < 0.05. Results showed a high spore population at 48 Weeks After Planting (WAP) in both locations for both years and no fertilizer application relatively led to a 12.7% increment in spore population in bot sites. A total of five AMF genera (Glomus, Acaulospora, Enthrospora, Gigaspora, and vii Scutellospora) were isolated from the soil while Glomus spp. predominated. Ploughing increased RC at Ido (26%) and Odeda (9%). Nitrosomonas spp. increased on single-ploughed flat and unfertilized plots. While there was inconsistency in the response of Nitrobacter spp to tillage and fertilizer application across locations in both years. At Ido, single ploughing led to 25%, and 13.4% increments in root yield in 2017 and 2018 respectively. While fertilizer application also increased yield by 13% in 2017 and a subsequent 13.4% in the preceding year. Similarly at Odeda, root yield increased on plots that were single ploughed and fertilized in both years. Plants with higher root yield had an increase in NPK accumulation and NPK concentrations increased under ZP. The study concluded that a combination of ploughing, ridging, and fertilizer application is favourable to high root yield in cassava and beneficial soil organisms such as AMF and some nitrifying bacteria.