Changes in the chemical fertility of a Mediterranean soil after the implementation of alley crops rotation in a mandarin orchard under regulated deficit irrigation

Intensive orchard monocultures in the Mediterranean region lead to environmental issues as soil erosion, soil organic matter loss and nutrient leaching. Alley cropping could serve as suitable strategy to improve soil fertility while increasing land productivity. This study aimed to assess the effect of different alley crop rotations on soil fertility and their effect on counteracting the effects of water stress on mandarin production. For this, three types of alley cropping with two different irrigation intensities were applied: i) a mandarin monoculture with bare alley soil, under both control irrigation (MM) and regulated deficit irrigation, RDI, (MMDI); ii) a multiple cropping of barley/vetch and fava bean, under both control irrigation (AC1) and RDI (AC1DI); and iii) a rotation of fava bean, purslane, and cowpea, under both control irrigation (AC2) and RDI (AC2DI). Soil samples were collected from two depths (0–10 cm and 10–30 cm) within the alleys, and different soil nutrients and cation exchange capacity (CEC) were measured. Chemical fertility in the MM treatment is relatively stable over time with time. A slight increase in the CEC was observed in AC1DI. In contrast, the AC2DI plots showed increases in B, P, and total nitrogen concentrations in subsurface samples. In terms of yield, this was significantly higher during the first year in MM, compared to AC1. Changes in production were similar in the three treatments. Average fruit size remained almost constant in MM but increased in AC1 and AC2. Regarding the productivity of the land, it decreased in MM and AC2 during the last year.