Soil change in Arenosols under long term cultivation in the sudano-sahelian zone of Cameroon

The effect of forest reserve conversion to agriculture land on soil properties in the sudano-sahelian zone of Cameroon was investigated. Agricultural activities have caused the progressive reduction of the surface area of Zamai forest reserve, which reduced from nearly 50% of its original surface in 1970 to only about one third in 2016. This study was conducted on four plots that have been cultivated for 3, 29, 50 and 90 years respectively, and a forest reserve soil used as control plot, all located along a chronosequence on Dystric Arenosols. The sandy fraction of cultivated soils varies between 70.00 ± 2.65 and 75.00 ± 2.65%, lower than that of the control soil (76.67 ± 3.21%). Silt contents were very low, but clay contents were higher in cultivated plots, with the highest proportion (28.66 ± 3.05%) seen in the 29 years cultivated plot. The stability index (SI) of different plots was greater than 9%, characteristic of stable structures. Compared to both 50 and 90 year cultivated soils, 3 and 29 years old agricultural soils had lower stability index and are thus more vulnerable to water and wind erosion in accordance with the lowest chemical characteristics observed. There was a gradual increase in acidity of cultivated plots from 3 years reaching higher values of 6.70 ± 0.24 and 6.49 ± 0.75 after 50 and 90 years of cultivation respectively. Ca²⁺ and K⁺ were the most represented bases. Moreover, there was an overall decrease in organic matter, sand and silt contents, SI and C:N, with a relative increase in clay content, pHw, K⁺, Ca²⁺, N, sum of bases and cation exchange capacity from 3 years cropping to 90 years. Control and 90 years cultivated plots were very similar, as a result of the restoration of soil properties after 90 years of farming activities, initiated from 50th year of farming activity.