Clean application of pistachio residues-based vermicompost with γ-aminobutyric acid can alleviate the negative effects of high soil pH on P uptake in saffron (Crocus sativus L.)

In semiarid areas dominated by calcareous soils, a large portion of available P may be deformed into insoluble structures due to the chemical activity of carbonate compounds. This phenomenon, known as P deficiency stress, is considered one of the most important limiting factors for saffron (Crocus sativus L.) production. To avoid P limitation, the application of clean and practical techniques has been emphasized to improve saffron adaptability grown in P-deficient calcareous soils. Hence, field experiments were conducted based on a factorial randomized complete block design with three replicates during 2017–2018 and 2018–2019 (farm 1) and repeated during 2018–2019 and 2019–2020 growing seasons (farm 2). Four levels of γ-aminobutyric acid (GABA) (0, 0.5, 1, and 2 mg L−1) and soil amendments (control, pistachio residues-based vermicompost (VP: 10 t ha−1; 50% in each growing season), sulfur (S: 100 kg ha−1; 50% in each growing season), and VP +S) were considered as experimental factors. From the results, application of VP, S, and VP+S decreased soil pH and increased Olsen-P, microbial biomass, and microbial respiration. Furthermore, the increase was observed for flower number, proline content and corm growth. Following GABA foliar application, flower number, proline content and P availability improved. Compared to control treatment, P concentration in large-sized daughter corms increased by 23.6, 16.8%, and 30.8%, following VP, S, and VP +S, respectively. Among the treatments, the highest P acquisition efficiency (39.2%) were recorded by applying VP +S along with 2 mg L−1. Overall, the results recommend the co-application of VP with GABA foliar spray to improve saffron production grown in calcareous soils of semiarid regions.