Effects of calcium and boron on leaf nutrition, fruit yield and quality of Changshanhuyou (Citrus changshanensis)

【Objectives】Studies on seasonal changes of nutrient elements contents in leaves are very important for investigating surplus-deficit status of plant nutrient elements and regulation of nutrient metabolism, and improving fruit yield and quality. We conducted a consecutive four-year field experiment to investigate the effects of calcium and boron fertilizers application on leaf nutrition, fruit yield and quality of Changshanhuyou.【Methods】The field experiment was conducted during 2010-2013 in 13-year-old trees of Changshanhuyou grafted on trifoliate orangePoncirus trifoliata (L.) Raf. in a commercial orchard in the Changshan Country, Quzhou City, Zhejiang Province of China. There were four treatments, 1) no chemical fertilizer (CK), 2) soil Ca application (0.5 kg calcium oxide per tree), 3) soil B application (25 g sodium borate per tree), and 4) soil Ca + B application (0.5 kg calcium oxide + 25 g sodium borate per tree). We sampled leaves located at the second or third position from the spring branch tip at different growth stages and fruits at the maturity stage, and analyzed the seasonal changes of mineral nutrient contents in leaves and the fruit quality.【Results】The contents of mineral elements in leaves are increased at the beginning and then declined in the entire period of fruit maturity. The contents of N, K, Mg and Zn reach their peaks at the stage of fruit set, and the P peak is at the fruit enlargement and the peaks of Ca, B, Fe, Mn and Cu are at the fruit swelling. The application of calcium or boron fertilizer improves the contents of Ca, B, N, K, Fe, Mn and Cu, and reduces the Zn content significantly. The interaction between Ca and B remarkably increases the Ca content in leaves in August and September. The average fruit yield for the 2 years is increased by 1.8%-21.4% in presence of different fertilizers, and the increased yields are in order: Ca+B＞B≥Ca. The accumulation yield for the 2 years of the B applied alone is significantly higher than that of the control and the combined application of Ca and B (Ca+B) could dramatically improve the yield. Ca, B applied alone have no significant effect on fruit quality, but Ca+B improves the ratio of soluble solid content to titration acid, and reduces titratable acid significantly.【Conclusions】 N, P, K, Mg and Zn are the main elements in absorption at the fruit-set phase, and elements such as Ca, B, Fe, Mn and Cu are mainly absorbed at the fruit enlargement stage. The combined application of Ca and B improves leaf mineral elements contents (except P and Zn), fruit yield and quality.