Integrating Silicon and Plant-Residue Mulching in Yellow Passion Fruit Under Semiarid Conditions: Effects on Leaf Physiology, Yield, and Fruit Quality

High evaporative demand under semiarid conditions can constrain leaf hydration and carbon assimilation in yellow passion fruit, motivating integrated silicon application and soil mulching strategies. This study evaluated soil-applied silicon (Si) and plant-residue mulch effects on physiology, yield, and fruit quality of Passiflora edulis Sims. A field experiment used a randomized complete block design with a 5 × 2 factorial arrangement, comprising five cumulative Si doses (0, 27, 54, 81, and 108 g plant−1), two mulch conditions (presence and absence), and four replicates. Mulch consisted of Cenchrus ciliaris and Megathyrsus maximus residues. Mulched plants exhibited higher predicted stomatal conductance and CO2 assimilation and lower transpiration throughout the evaluated dose range. Increasing Si doses increased relative water content and reduced electrolyte leakage under both conditions. Maximum predicted yields were 31.29 t ha−1 with mulch at approximately 58 g plant−1 and 21.64 t ha−1 without mulch at approximately 55 g plant−1. With mulch, maximum predicted fruit mass and seedless pulp mass reached 327.86 and 114.68 g, respectively. Pulp pH, titratable acidity, total soluble solids, and the TSS/TA ratio showed quadratic responses. Intermediate Si doses combined with plant-residue mulch favored yield under the evaluated conditions, whereas doses associated with maximum physiological responses and fruit attributes differed.