Abstract. This analysis compared the suitability of contiguous fallow-forest lands for cassava, yam, cocoyam and sweet potato production in Nsukka, south-eastern Nigeria. The fallow plots were brought into cultivation in 1998 under the IITA-UNN long-term collaborative research. The sole cassava plots were grown to cassava only continuously for five years and then left to fallow. Soil samples were collected from 0-20 cm depth in triplicates using an auger and core sampler from the seven representative fallow plots previously grown to sole cassava from 1998-2003 and under fallow till date as well as the adjacent forest land. The objective was to use the soil qualities as recovered during the fallow period and those from the original adjacent forest to determine their current suitability for the production of the four crops. Using the FAO's principle of limiting conditions revealed that after 13 yrs of fallow, the plots grown to sole cassava was classified as highly suitable (S1) for sweet potato production but moderately suitable (S2) for cassava, yam and cocoyam production. The remnant forest land was highly suitable for sweet potato production but moderately suitable for cassava, yam and cocoyam production. The dominant soil limitations are organic matter, low cation exchange capacity and exchangeable potassium for both cassava and yam production. The major limitations to cocoyam production are low available phosphorous, base saturation and soil pH. If these constraints are addressed adequately by soil nutrient management programmes all the plots will scale up to S1 class for the four crops.

Forest land provides a wide range of ecosystem services such as reducing the impact of raindrops on the soil and maintenance of soil fertility, whereas fallowing is one method used in restoring the fertility status of degraded farmlands. This study evaluated the physicochemical properties of an Alfisol under fallow and adjacent forestland, and their suitability for cocoyam, pigeon pea, and sweet potato. The fallow plots were brought into cultivation in the year 1998 under the IITA-UNN long-term collaborative research. Soil samples were collected from 0-20 cm depth in triplicates using an auger and cylindrical core from the seven representative fallow plots previously grown to sole cassava from the year 1998–2003 and under fallow till the year 2016 as well as the adjacent forest land. The result obtained showed that the fallow land had higher fertility nutrients than the forest land in the year 2016. The fallow land gave the highest values of SOC, total nitrogen, percentage base saturation, total exchangeable bases (Ca2+, Mg2+, Na+, K+) and exchangeable acidity when compared with the forest land. Using the FAO’s principle of limiting conditions as guide, both fallow and forest soils are marginally suitable (S3) for cocoyam production but highly suitable (S1) for both pigeon pea and sweet potato production.