Production Indicators in Cowpea as a Function of the Water–Fertiliser Nexus

The bean is an important crop in feeding the global population. In the northeast of Brazil, it is of particular importance, since it is a staple food, which also generates employment and income. The low productivity of the northeast in recent years due to the water crisis combined with the cost of energy has compromised technical and economic viability. This study aimed to evaluate production parameters of cowpea (Vigna unguiculata (L.) Walp.) under different alternative production systems in the northeast of Brazil. The study was carried out in the experimental area of the sewage treatment plant (STP) in the district of Tianguá, Ceará. The experiment comprised six production systems (treatments) divided into split plots distributed in a completely randomised design with fifteen replications. The systems irrigated with wastewater and amended with different of fertilisers were no fertiliser (S2A0), mineral fertiliser (S2A1) and organic fertiliser (S2A2), as well as systems irrigated with drinking (S1A0, S1A1 and S1A2). It was found that under the systems irrigated with wastewater, the average productivity was 1468.8 kg ha−1, whereas under the systems irrigated with drinking water, it was 984.1 kg ha−1. The production systems that used wastewater (S2A0, S2A1 and S2A2) resulted in greater productivity compared to the production models irrigated with drinking water with organic fertiliser (S1A2) and with no fertiliser (S1A0). All the production models irrigated with wastewater yielded similar results to the conventional system with mineral fertiliser, showing that treated wastewater contains sufficient nutrients to potentially replace mineral fertilisers in cowpea production in the northeast of Brazil. The use of treated domestic effluent increases the productivity of irrigated crops.