Diatomaceous Earth as a Silicon Source for Mango Trees in the Submiddle São Francisco Valley

Abstract OBJECTIVE: To evaluate the effects of diatomaceous earth application as a source of silicon (Si) on gas exchange and the nutritional status of mango trees (Mangifera indica L.) cv. ‘Palmer’ grown under semiarid conditions in the São Francisco Valley. MATERIAL AND METHODS: Mango trees (Mangifera indica L.) cv. ‘Palmer’ were subjected to diatomaceous earth application as a silicon (Si) source. Treatments consisted of an untreated control and soil applications of diatomaceous earth (50 and 100 kg ha⁻¹), either alone or combined with foliar spraying (1 and 2%). Leaf samples were collected at two phenological stages to determine macronutrient, sodium (Na), and Si concentrations. Gas exchange was evaluated to determine the effects of Si application on plant photosynthetic activity. RESULTS: Diatomaceous earth application affected only stomatal conductance, reducing it by up to 24% during the first production cycle, without altering CO₂ assimilation rate, transpiration, or chlorophyll indices. Leaf P concentrations were not affected, whereas N, K, Ca, Mg, and S showed responses that depended on phenological stage and production cycle. The highest Si dose increased leaf Ca and Mg concentrations, reduced S concentrations, and decreased Na accumulation by up to 33.6%. Leaf Si concentrations did not consistently increase with diatomaceous earth application. Mango yield was not affected by the treatments in either production cycle. CONCLUSION: Diatomaceous earth application as a Si source promoted specific adjustments in the physiology and nutritional status of ‘Palmer’ mango trees, without increasing leaf Si concentrations or yield. Under the irrigated conditions of the Submiddle São Francisco Valley, its effects were limited, suggesting greater potential for use under conditions of more intense abiotic stress.