Potentials of Calliandra calothyrsus Meissner for improving soil fertility and maize performance in the forest savannah transition zone of Cameroon.
Farmers identified low fertility as a major problem affecting crop yield in Mbam Division, a forest-savannah transitional zone of Centre Cameroon. An experiment was therefore carried out in farmers' fields in Kiki village for four consecutive years in order to investigate the effect of Calliandra calothyrsus planted fallow on soil fertility and maize yield improvement, as compared to natural fallow. The experimental design for each year was a randomised complete block with two fallow treatments (planted and natural) and nine replications (farms). In the first year, Calliandra calothyrsus fallows were established in nine farmers' plots and plant growth was monitored for 12 months. From the second year, Calliandra trees were pruned each year in the first cropping season and maize (Zea mays L.) was grown between the Calliandra rows. Composite soil samples were collected from 0-15 and 15-30 cm soil depths at the beginning and at the end of the experiment, and were analysed for chemical properties. Cluster analysis (CA) was applied to the soil data to evaluate the comparability of the nine experiment farms. Analysis of variance and means separations (Tukey's method) were used to evaluate the effects of treatments on soil and maize yield. CA grouped the experimental farms into two different soil series named series 1 (n=6) and series 2 (n=3), differentiated mostly by the organic matter and exchangeable cation contents. After 12 months of Calliandra growth on the two soil series, average tree height was 2.07 m and diameter at breast height 1.7 cm; but, with a relatively low biomass production (0.92 t.ha-1 leaf and 1.6 t.ha-1 wood biomass). The natural fallow produced less total biomass than planted fallow (1.3 t.ha-1 herbaceous biomass). Despite this low biomass production, Calliandra treatments significantly (p<0.05) increased pH, exchangeable bases and ECEC in both soils, as compared to natural fallow biomass. Maize grain yields also increased significantly (p<0.05) every year under Calliandra treatment in the two soil series, producing 45% (series 1) and 55% (series 2) extra yields in the third year as compared to the first year. The majority of farmers were favourably disposed to adopting this technology although they recognized some related constraints such as extra equipment and labour.