Unravelling sustainable intensification in oil-palm agroforestry on the Adja plateau, Benin

Pathways for mediating the competing land-use claims of landowners and tenants in oil palm agroforestry systems in Benin’s Adja plateau do not consider the diversity of land-management practices. Therefore, we analysed how soil properties and maize yields in those systems are affected by two contrasting categories of land-management practices and fertilisation options. We used a synchronic approach to split these practices and options into two successive steps. In Step 1, referred to as cropped fields, tenants continuously intercrop maize among scattered oil palms. In Step 2, referred to as fallows, the land is densely planted with oil palm, without intercropping. Twelve farmers’ fields were selected for this study. Eight represent cropping fields, and four are 15-year-old oil-palm fallows. Cropped field fertilisation treatments consisted of farmyard manure (at 15 and 30 t ha−1) and mineral fertiliser (150 kg ha−1 of N14P18K18S6B1 + 50 kg ha−1 of urea). We found no significant differences between the N contents and C:N ratios of the two types of fields. However, the numbers and masses of earthworm casts were higher in cropped fields treated with farmyard manure than with mineral fertiliser. Farmyard manure (15 and 30 t ha−1 rates) also produced significantly higher maize yields (respectively, 2.5 and 3.2 t ha−1) than the mineral fertiliser alone (1.9 t of maize per ha). We conclude by discussing N, K and P storage in soil, and recommended use of farmyard manure as an agroforestry practice that will benefit landowners and tenants alike on the Adja plateau.