Growth and Gas Exchanges of Arugula under Phosphate Fertilisation and Irrigation Depths

Aims: To study the growth and gas exchanges of arugula plants under water stress and phosphate fertilisation as attenuator.

Study Design: The experimental design was randomised blocks, with treatments arranged in a 5 x 2 factorial scheme, corresponding to five doses of P2O5 (0, 50, 100, 150 and 200 mg dm-3) and two irrigation depths, 50% of the real evapotranspiration (ETr) and 100% ETr, with four replicates, totaling 40 experimental units.

Place and Duration of Study: The experiment was carried out in a protected environment of the Center of Sciences and Agrifood Technology (CCTA) of the Federal University of Campina Grande (UFCG), Campus of Pombal-PB, Brazil, in the period from February 2 to March 31, 2015.

Methodology: Phosphorus (P) was applied 10 days before seedlings transplantation, which was homogenised. The source was single superphosphate, which has the following composition: 18% of P2O5, 16% of Calcium (Ca) and 8% of Sulfur (S). The real evapotranspiration was determined through weighing lysimetry in the treatments that received 100% ETr. For that, the weight of the pots at field capacity (WFC) (kg) was determined from the saturation through capillarity followed by drainage until constant weight, which was considered as WFC. The pots were daily weighed to obtain the actual weight (Wa) (kg) of each pot.

Results: The dose of 200 mg dm-3 under 100% ETr leads to the best production of fresh leaves of arugula; Phosphorus application improves the gas exchanges of arugula plants cultivated under 50% ETr, with the dose of 104 mg dm-3 P2O5 delivering the greatest gains in CO2 assimilation rate.

Conclusion: Arugula growth and phytomass formation are reduced when plants are cultivated under 50% ETr, However, phosphorus application optimises the osmoprotection process of the arugula plants, but does not promote the increase of production under water deficit conditions.