Productivity of Opuntia ficus-indica (L.) Miller under different N and P fertilization and plant population in north-east Brazil

The arid and semi-arid region occupies 89.3% of north-east Brazil, and livestock farming is one of the most important activities in this region. Experiments were conducted in four locations in the semi-arid of Pernambuco, Brazil. The objective was to study N (0, 75, 150, 225, and 300 kg N ha−1 yr−1) and P fertilizations (0 and 33 kg P ha−1 yr−1) at two populations (5000 and 40 000 plants ha−1) of Opuntia ficus-indica (L.) Mill. Increasing population from 5000 to 40 000 plants ha−1 increased productivity in all four sites. Phosphorus fertilization increased dry matter yield (DMY) only when soil P was <10 mg kg−1. Nitrogen fertilization increased linearly DMY in the higher population, but no response to N was observed with 5000 plants ha−1. Nitrogen fertilization also increased plant N concentration and rainfall use efficiency. Cladode area index (CAI) increased with population but even in the higher population the CAI was 1 or less. In summary, increasing plant population and fertilizing with N and P resulted in greater productivity of O. ficus-indica in north-east Brazil. Phosphorus fertilization involved less economical risk to the farmer but positive responses occurred only when soil P was <10 mg kg−1.