Abstract
The adaptability of cassava to low fertile and marginal soils facilitates its production in subsistent agriculture. As a result, smallholder farmers rarely apply fertilizers. The current yield gap is therefore very large, calling for application of fertilizers and soil amendments to improve its productivity. Field experiments were carried out to assess the potential of partially substituting Phosphorus (P) fertilizers by in vitro-produced arbuscular mycorrhizal fungal (AMF) inoculants in cassava production in two agro-ecologies of Nigeria: Northern Guinea Savanna (Samaru) and Sudan Savanna (Minjibir). The experiments were laid out in a split plot design with P levels (0, 17.5, 35 and 52.5 kg P2O5 ha-1) as main plot and AMF inoculants (Control, Glomygel, Glomygel carrier, Mycodrip, Mycodrip carrier) as subplots. The results in Samaru showed that there was significant interaction between AMF and P in root fresh weight, total biomass and root to shoot ratio. The root fresh weights of the inoculated cassava increased proportionally with application of P. However, highest root fresh weight of cassava inoculated with Glomygel was observed at 35 kg P2O5 ha-1 recording 25% yield increase compared to 52.5 kg P2O5 ha-1 application. Interestingly, Cassava inoculated with Glomygel at 17.5 kg P2O5 ha-1 gave root fresh yield statistically similar to where 35 kg P2O5 ha-1 was applied. This represented a 50% reduction in P fertilizer use. Also, cassava inoculated with Glomygel increased leaf nutrient concentrations, which strongly correlated with the root fresh yield. However, no effects of inoculant carriers were observed in yield and nutrient concentrations. Contrarily, there was no significant treatment effect in Minjibir for nearly all the measured parameters. Cassava yield was however, higher in Minjibir than Samaru probably due to soil fertility and structural differences, which resulted in few observable effects of AMF and P treatments at Minjibir. We conclude that under low P conditions inoculation with in vitro produced AMF inoculants could be employed to reduce P fertilizer requirements for cassava and improve yields, but the variability of the responses as a result of soil heterogeneity and the identity of the fungal strain in the inoculant require further investigations before recommending the practice.
Highlights
Phosphorus (P) is one of the most important determinants of plant growth and in most soils it exists in forms that are largely unavailable for plant uptake [1]
Kamara et al [4] reported that P levels were lower than critical values of 7 mg kg-1 (Mehlich-3 extractable P) in 92% and 93% of the fields surveyed in the Northern Guinea savanna and the Sudan savanna of Nigeria, respectively
Co-application of P fertilizer and in vitro arbuscular mycorrhizal fungal (AMF) inoculants in the Northern Guinea Savanna (Samaru) and Sudan Savanna (Minjibir) of Nigeria showed a strong site effect demonstrating the need of local adaptation of the practices
Summary
Phosphorus (P) is one of the most important determinants of plant growth and in most soils it exists in forms that are largely unavailable for plant uptake [1]. Such is the case with Nigerian soils, which are mostly Oxisols, Ultisols and Alfisols [2]. Phosphorus can be as low as 2 mg kg-1 in the savanna soils of Nigeria [3] making P one of the most limiting nutrients in those soils. Overcoming P deficiency in soils of savanna zones of Nigeria is one of the major challenges that smallholder farmers are facing. There is a need to provide cost-effective alternatives in order to increase the adoption of high quality agricultural inputs by reducing the cost of production, while enhancing crop productivity
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