Abstract
Three inoculation trials with soybean, cowpea and groundnut were conducted on Eutric Cambisols (EC) and Rhodic Nitisols (RN) in a greenhouse. Five rhizobial inoculants: MAR 1495, TSBF Mixture, Legumefix, HiStick and IRJ 2180A were tested on each crop to determine their response to soil type and ability to form symbiotic relationship with the crops. Generally, response to inoculation was found to be significantly higher (P < 0.05) in EC than RN. In soybean and groundnut trials, highest nodulation in both soils was recorded by strain MAR 1495 followed by TSBF Mixture and these were significantly higher (P < 0.05) than other inoculants and control. A similar trend, though only in EC, was observed in N uptake and in nitrogen fixation but no significant difference was observed in dry matter yield. Cowpea trials did not show response to inoculation nor was there difference between the soils. Instead, control treatment surpassed all the inoculated treatments in nodulation at P < 0.05. Nitrogen uptake and N2 fixation of control also surpassed those of inoculated treatments. Rhizobia strains MAR 1495 and TSBF Mixture showed similar ability to improve the productivity of soybean and groundnut thus can be used as common inoculants for the two crops. Key words: Rhizobial inoculation, Eutric cambisols, Rhodic nitisols, nodulation, dry matter yield, N uptake, N2 fixation.
Highlights
Continuous depletion of nitrogen (N) from the soil pool by processes such as volatilization, leaching and, perhaps most importantly, removal of nitrogen-containing crop residues from the land results in the decline of soil N reserves in agricultural soils
According to FAO classification (2006), Mokwa soil is classified as Rhodic Nitisols (RN) while Shanono soil is classified as Eutric Cambisols (EC)
EC is slightly acidic while RN is moderately acidic (Table 2)
Summary
Continuous depletion of nitrogen (N) from the soil pool by processes such as volatilization, leaching and, perhaps most importantly, removal of nitrogen-containing crop residues from the land results in the decline of soil N reserves in agricultural soils. Prolonged applications of large quantity of these N fertilizers are manifesting themselves in environmental degradation such as leaching of nitrates into the ground water and development of soil acidity (Ridley et al, 2004; Agbenin and Goladi, 1997). Most farmers cannot afford these inorganic fertilizers. Over 90% of Nigerian farmers use inorganic fertilizers, but in majority of cases they apply only half the amount that is recommended because of the cost involved (Sanginga, 2003). The economic and environmental costs of the heavy or wrong use of inorganic nitrogen fertilizers in agriculture are a global concern and mandates that alternatives be urgently sought
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