Effect of arbuscular mycorrhizal fungi and different phosphorus rates on selected soil and growth parameters of two dry bean cultivars

Abstract

Dry bean is one of the most important cash crops and source of protein for small holder farmers. Low yields of dry bean are often reported to be associated with lack of inoculation (Arbuscular mycorrihizal fungi) of seeds prior to planting. Soil phosphorus (P) unavailability is one of the major factors limiting yield of dry bean. Field and Greenhouse experiments were conducted to investigate the response of dry bean cultivars to inoculation and phosphorus application under dry land farming conditions at the Syferkuil experimental farm of University of Limpopo. Both greenhouse and field experiments were carried out as a split-split plot arrangement in randomised complete block design with four replications. Main plot treatment comprised of two dry bean cultivars VIZ, red speckled bean and small white haricot. Arbuscular mycorrhizal fungi inoculation levels (inoculated and uninoculated) were assigned in the sub-plot whilst the sub-sub plot was applied with five phosphorus rates at 0, 20; 40; 60 and 80 kg/ ha using single superphosphate (10.5 % P). The data collected were subjected to analysis of variance using statistical software (ANOVA) STATISTIX 10.0.Dry bean cultivars (red speckled bean and small white haricot bean) were evaluated in a field experiment for their growth, nodulation and yield responses to AM fungi inoculation and different rates of P fertiliser. The results revealed that the red speckled bean had higher number of nodules (45 %), stem diameter 26.96 cm and higher leaf area of 21.05 cm2 as compared to small white haricot bean. The application of P at the rate of 40 kg/ha produced higher grain yield of 743.47 kg/ha as compared to small white haricot bean with 572 kg/ha. The growth parameters such as yield, soil chemical and biological properties did not significantly respond to inoculation (P≤0.05). Red speckled bean and small white haricot bean were evaluated in greenhouse experiment for their growth and nodulation on inoculation and phosphorus fertilizer treatment In the greenhouse experiment phosphorus fertilizer rate showed significant effect on chlorophyll content, leaf fresh and dry weight. The dry bean cultivars were found to be significant to number of nodules, plant vigour and root dry weight. The red speckled bean showed higher growth parameters as compared to small white haricot bean. The application of Arbuscular mycorrhizal fungi (AM fungi) at varying rates did not have any significant influence on all parameters measured in the experiment on both trials. The study needs to be repeated after 4 to 5 years. The findings of this study concluded that P should be applied at the rate of 40 kg P/ha in order to improve the production of dry bean.