Phosphate Fertilizer Sources and Doses Affect Yield and Nutritional Quality of Kale Under Organic Management

The search for a healthy diet has increased the consumption of kale, a vegetable recognized for its high nutritional value, mineral content, and antioxidant properties. Phosphorus is an essential nutrient in this context, acting in energy transfer and root development, which favors productivity and product quality. This study evaluated the effect of two phosphorus sources, bone meal (BM) and thermophosphate Yoorin® (TY), and five phosphorus (P2O5) doses (0, 160, 320, 480, and 640 kg ha−1) on kale yield and quality. The experiment used a randomized complete block design with four replications and ten treatments in a 2 × 5 factorial arrangement in a protected environment over a cycle of 155 days after transplanting. Marketable yield with BM reached an estimated maximum of 1.54 kg plant−1 at 525 kg ha−1 P2O5 (54% over control), while TY showed a linear increase up to 1.57 kg plant−1 (59%). Photosynthetic pigments, antioxidant activity, ascorbic acid, and total phenolic compounds fitted quadratic models, with gains of up to 36%, 73%, 51%, and 57%, respectively. Contents of P, K, Ca, and Fe increased significantly with P doses, with Fe gains reaching 110–180%. Phosphate fertilization with BM, a renewable P source, increases kale yield and nutritional quality, highlighting its potential for organic farming systems.