Growth, nodulation and yield response of promiscuous and non-promiscuous soybean cultivars to inoculation in different soil types under classhouse and field conditions

Abstract

Soybean (Glycine max (L.) Merrill) is considered to be an important grain legume and an oil crop. It is also important in livestock feeding and improvement of soil fertility through biological nitrogen fixation (BNF). Until recently, soybean was not widely grown by smallholder (SH) farmers in Africa. This has led to breeding of promiscuous varieties to ensure wide adoption of the crop by SH farmers, without the use of inoculants or expensive nitrogen fertilizers. Field and glasshouse experiments were conducted during 2012/2013 growing season. One commercial (specific) variety Dundee and three naturally-nodulating (promiscuous) soybean varieties (TGx-1937-1F, TGx-1740-2F, TGx-1835-10E) were evaluated in a field trial for their growth, nodulation and yield response to B. japonicum strain WB74 inoculation. Seed inoculation in the field enhanced chlorophyll content, number of nodules, nodule dry weight, and the percentage of active nodules, number of pods, hundred seed weight, shelling percentage and grain yield. Varietal differences exerted significant (P≤0.05) effect on all field parameters evaluated except on nodule number and percentage of active nodules. TGx-1937-1F achieved the highest number of nodules (28 per plant) while the highest percentage of active nodules (69%) was achieved by TGx-1740-2F. Huge effect of inoculation was observed on Dundee variety, and resulted in significant grain yield increases (237.8%) while smaller gain increases were observed in TGx-1740-2F (43.9%) and TGx-1835-10E (38.7%). The yield of TGx-1937-1F did not respond to inoculation. Two promiscuous (TGx-1937-1F and TGx-1740-2F) varieties and one commercial (Dundee) variety were evaluated in a glasshouse trial for their growth and nodulation response to inoculation in different soil types (sandy clay loam, sandy loam, loamy sand) of Limpopo Province. In the glasshouse inoculation showed effect on chlorophyll content only, and effect of soybean variety was found to be significant on days to flowering, chlorophyll content, plant height, number of nodules and root dry weight. Soil type showed significant effect on all parameters evaluated in the glasshouse study except on nodule dry weight. Loamy sand soil from Ga-Molepo gave tallest plants and highest nodule number at 61 cm and 29 nodules/plant compared to other soils. All soils evaluated in the study resulted in percent active nodules ranging from 74.5% to 77.4% showing possibility of presence of cowpea-type rhizobia in Limpopo soils capable of fixing atmospheric nitrogen. Inoculation x variety interaction was significant on days to flowering, plant height and chlorophyll content. Inoculant application in TGx-1740-2F variety reduced the number of days it took to flowering from 61 to 54 days and increased its plant height by 57% from 44.8 to 67.9 cm. Eighty three percent (83%) increase on chlorophyll content of variety Dundee was observed due to effect of inoculation. Inoculation x soil type interaction had significant effect on plant height and dried plant biomass. Varity x soil type interaction influenced chlorophyll content, while the interactive effects of inoculation x variety x soil type were significant on chlorophyll content only. The study showed that it is beneficial to inoculate the soybean varieties studied, especially the commercial variety Dundee, in order to enhance their growth, nodulation and yield.