Effect of coal ash fly zeolite and Bacillus subtilis on water-use efficiency of chickpea grown under water deficit

Chickpea cultivation may be considered strategic for improving sustainability in Mediterranean cropping systems; however, global warming and drought may pose limitations to yield stability. Soil amendments, such as zeolite (Z), and microbial inoculation with plant growth-promoting bacteria (PGPB) are indicated as potential strategies to mitigate water deficiency. Still, their combined application has been little investigated, especially in pulse crops. To evaluate the effects of synthetic zeolites, PGPB inoculation, and water deficit on chickpea, a pot experiment was carried out under controlled conditions. Two chickpea genotypes (Pascià and Sultano) were subjected to a factorial combination of 2% soil-added zeolite and PGPB under optimal and limiting water conditions (100 and 50% of the water requirement, respectively). The results showed that water supply strongly influenced crop response, with a reduction of about 50% in grain yield under water deficit. Treatments with zeolite and PGPB (Bacillus subtilis) inoculation led to a significant increase in yield and water-use efficiency (WUE) on both chickpea genotypes under water deficit, and their combination further improved harvest index. Under non-limiting water conditions, the increase in WUE was significant with PGPB inoculation. An increase in protein content (PC) was also observed in plants treated with zeolite under water-deficit conditions, while grain total phenolic content (TPC) was negatively influenced by water supply. Overall, agronomic treatments mitigated the effects of water deficit: zeolite improved harvest index and nitrogen uptake while PGPB enhanced WUE. Their combined use appears promising as a strategy to alleviate the negative impacts of water deficit on chickpea cultivation.