Abstract
Improving biological nitrogen fixation through legume nodulating bacteria (LNB) inoculation requires knowledge on the abundance and effectiveness of indigenous population in the ferralsols. The Most Probable Number method (MPN) was used to determine the naturally occurring LNB population in 64 representative soils of four sites in the humid forest zone of Cameroon. Nodulation Macroptilium atropurpureum was examined under tubes experiment in four location sites: Bertoua, Ebolowa, Bokito and Yaounde, and within each of the locations, in four land use systems (LUSs) of different levels of disturbance: mixed farm; fallows; cocoa plantation and forest. The LNB population size varied from 0.78 to 5.25 log units of soil depending on the land use. The most disturbed LUSs (farms and fallows) exhibiting the highest number of LNB on average. Undisturbed ones (cocoa plantation and forest) showed the lowest number of LNB. The percentage of the need for inoculation was more frequent in the forests (94%) and plantations (75 %). It is low in the in the fallows (25%) and the farms (44 %). In total 60 % of the soils analysed need inoculation. These results are important for future investigations on alternative inoculant strains for improving legume production in Cameroon.
Highlights
Ferrallitic red soils of the humid-forest zone of southern Cameroon are known to be generally of low fertility, for nitrogen and phosphorus availability
The soil aluminium content was consistently lower in the fallow (0.34 meq/100g) than in other land use systems (LUSs) at Bertoua (p = 0.025), whereas at Bokito, it was significantly lower (p = 0.013) in the forest (0.28 meq/100g) than the plantation (0.49 meq/100g)
Soils of the humid forest zone (HFZ) of Cameroon contain legume nodulating bacteria (LNB) and an important variation was noticed on the number of LNB according to site and land use
Summary
Ferrallitic red soils of the humid-forest zone of southern Cameroon are known to be generally of low fertility, for nitrogen and phosphorus availability. While the use of nitrogen (N) fertilizers is one of the best mean to farmers to reduce N deficiencies in Cameroon, their use is limited by their cost and availability These fertilizers may induce soil acidification and become less efficient after few cropping seasons [1], leading to a high dependence of soil to N fertilizers for optimum yield [2]. High N fixation, requires the presence of adequate numbers of highly effective legume nodulating bacteria (LNB) in the soil [4]. Wherever a particular legume is considered as a traditional crop, it is likely that there will be adequate numbers of indigenous LNB for inoculation [6] Beyond this generalisation, it is difficult to predict situations where inoculation might not be necessary in tropical soils
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