Interação entre adubação N/K e calagem nas respostas fisiológicas da palma forrageira em condições de semiárido

Abstract

Forage cactus is strategic in the semiarid region, especially during seasonal droughts when it serves as feed for livestock. However, the integrated response to nitrogen/potassium fertilization (N/K) and soil acidity correction (liming) remains poorly understood. We aimed to quantify the isolated and combined effects of N/K and liming on photosynthetic pigments, growth, and antioxidant enzymes of the cultivar ‘Orelha de Elefante Mexicana’. A randomized block design evaluated 13 N/K combinations under two liming conditions (with/without) and four replications; chlorophylls (a, b, total, a/b), carotenoids, proteins, biomass, water content, and the activities of SOD, CAT, and APX were measured. Data were analyzed by factorial ANOVA, Scott–Knott test, Pearson correlation, and PCA. A liming × N/K interaction was detected for pigments and for SOD and APX. Overall, liming increased chlorophylls, most notably at 109/180 kg ha⁻¹ N/K, and under acidic soil, 46.8/420 kg ha⁻¹ maintained high values; carotenoids tended to be higher in acidic soil. For enzymes, SOD and APX increased with liming, whereas CAT was more demanded under acidity, suggesting greater peroxide detoxification. PCA revealed a gradient between chlorophylls and SOD/APX/carotenoids, indicating a trade-off between photochemical investment and antioxidant protection depending on N/K balance and pH. The best physiological performance results from correcting soil acidity when limiting and jointly adjusting N and K at moderate, balanced rates, avoiding K excess applied alone, to sustain the photosynthetic apparatus under semiarid conditions.