Spatial and temporal variation in crop productivity and relation with soil fertility within upland agroforestry

Agroforestry can be an option of sustainable farming practices for upland communities. However, information of spatial and temporal variation in soil fertility and crop productivity along slopes, which can guide e.g. effective management, such as application of fertilizers, is limited. This study evaluated spatial and temporal variability in crop productivity and soil fertility along slopes in two different fruit tree agroforestry systems in upland areas of north-west Vietnam: (1) longan-mango agroforestry integrating longan ( Dimocarpus longan L.), mango ( Mangifera indica L.), maize ( Zea mays L.), and guinea grass ( Panicum maximum Jacq.), and (2) plum agroforestry integrating plum ( Prunus salicina L.), maize, and guinea grass. The two systems were established on relatively steep slopes, 37 % and 65 % slope, respectively. Crop performance and soil fertility were measured in different positions relative to the fruit tree-grass rows over 4–5 years and compared with sole-crop maize. The results showed that maize height, grain yield, and leaf nitrogen (N) concentrations were significantly higher at the upslope than downslope side of tree-grass rows. For example, the grain yields were 30–35 % higher at the upslope than downslope side. Regarding soil fertility, there was a tendency that SOC, total N, total phosphorus (P), available P, and available potassium (K) were higher at the upslope than downslope side of tree-grass rows. Thus, the forage grass strips played an important role in trapping N and other nutrients, and enhanced nutrient use efficiency within agroforestry at the steeply sloping study sites. The maize performance and soil fertility in the areas mid-way between two tree-grass rows were comparable to those in sole-crop maize. The results of this study can provide guidance for farmers managing fruit tree agroforestry in north-west Vietnam or other regions with similar cropping, climate, and biophysical characteristics to implement more effective plot management practices on sloping land. • Variation in crop productivity and soil fertility along slopes in upland agroforestry was studied. • Maize growth and yields were higher at upslope than downslope side of fruit tree-grass rows. • A similar trend was found regarding soil organic and nutrient content. • Fruit tree-grass rows played an important role in creating the spatial and temporal variability. • Such variability should be considered for effective application of nutrients in agroforestry.