Modulation of Leaf Ionic Composition and Yield of ‘Formosa’ Papaya by Specific Biostimulants Under Deficit Irrigation

This study evaluated the effects of biostimulant treatments on the ionic composition and yield of ‘Formosa’ papaya (Carica papaya L.) subjected to varying water replacement levels. The research utilized a randomized complete block design in a split-plot scheme comprising three irrigation depths (100%, 75%, and 50% ETc) and four biological treatments: control, Trichoderma harzianum, Ascophyllum nodosum, and Bacillus aryabhattai. Contrary to initial expectations, water restriction was associated with increased yield and leaf concentrations of zinc (Zn) and nitrogen (N), challenging the hypothesis that water restriction limits production. Quantitative results showed that T. harzianum under 75% ETc attained 93.29 kg plant−1, whereas the control at 50% ETc recorded 19.14 g kg−1 of N. Under 50% ETc, B. aryabhattai increased the bacterial population to 10.46 log10 CFU g−1 soil compared to the control. The T. harzianum-based biostimulant reduced leaf sodium (Na) under 75% ETc and maintained the nutrient accumulation order K > N > Ca > Fe > Mn > Zn > Cu > Na. Conversely, B. aryabhattai and A. nodosum improved yield under 100% ETc through N accumulation. This study confirms that microbial and seaweed-based biostimulants mitigate water stress through rhizosphere modification and nutritional homeostasis, offering a practical strategy for sustainable fruit production in semi-arid regions.