Soil samples were taken on sisal plantations in Tanga region (Tanzania) in order to investigate changes in soil chemical properties resulting from permanent cropping. Differences in soil fertility decline of eight Major Soil Groupings (FAO-Unesco) were evaluated by comparing (i) data from different soils under permanent cropping, (ii) data from the same soils under bush vegetation and permanent cropping, (iii) soil analytical data for fields which were sampled in the 1950s and 1960s and resampled in the 1980s and 1990s. Differences in soil fertility decline between the Major Soil Groupings were large. Ferralsols and Acrisols under permanent cropping had strongly acid soil reactions and low levels of fertility. The pH of Ferralsols and Acrisols under permanent cropping was 1.2 to 1.4 units lower in both topsoils and subsoils when compared to bush vegetation. Also exchangeable cations and base saturation were significantly lower under permanent cropping. Organic carbon was only significantly lower in the topsoils of the Ferralsols. Exchangeable aluminium was higher under cropping than under bush vegetation in the subsoils of both Major Soil Groupings. The historical data revealed a highly significant decline in both pH and exchangeable cations of the topsoils of the Ferralsols. Cambisols and Luvisols showed resilience despite them being permanently cropped for over 60 years with little or no fertilizer inputs during the past two decades. Phosphorus and potassium had also been reduced to very low levels in these soils. Similar observations were made in Leptosols and Phaeozems. Statistical analysis showed that there were no differences between the 1950s and 1960s and 1980s and 1990s in pH and exchangeable calcium and magnesium of the Cambisol topsoils; only the exchangeable potassium had decreased significantly in the Cambisols. Although the data of some Major Soil Groupings were few, all three approaches have shown that soil analytical data at the Major Soil Groupings level can be of use for the assessment of soil fertility decline.