Dynamic changes of nutrition in litchi leaves and effects of potassium and nitrogen fertilization

【Objectives】Field experiment was conducted to determine the annual changes of element contents in litchi leaves and the effects of the nitrogen (N) and potassium (K) ratio on the yield and planting benefits of litchi，aiming to provide a theoretical basis and practical guidance for fertilization management, nutrition regulation in litchi production. 【Methods】The cultivar Feizixiao litchis，the main domestic grafted seedlings, were planted in 1995 and taken as tested material. Field experiments with different ratios of potassium over nitrogen (K2O/N: 0.6, 0.8, 1.0, 1.2 and 1.4) were conducted in the main litchi plant region of Guangdong in the 3 growth seasons from 2009 to 2012. Litchi leaves were collected periodically to measure the contents of mineral elements. When litchis are ripe, the actual yields of litchis were weighed in the field.【Results】The nutrient contents in litchi leaves vary significantly in different growing stages. During the whole growing period, the contents of nutrient elements in litchi leaves are in order of N K Ca Mg P S B Zn Mo. The K content is highly and negatively correlated with the contents of Ca and Mg, and significantly and negatively correlated with that of Zn. The contents of Ca, Mg and Zn are positively and significantly correlated with each other. The N content is negatively and significantly correlated with the those of S and B in leaves, and the contents of S and B show significant positive correlation with each other. The content of P exhibits significant negative correlation with Ca and Si, while the contents of Ca and Si are significantly and positively correlated with each other. Under the same N application rate, the yield and planting benefits of litchi are increased at first with the increase of ratio of K2O to N and then decreased. Litchi has the highest yield and benefit when the ratio of K2O to N ranges from 1.0 to 1.2. 【Conclusion】The ratio of K2O to N ranges from 1.0 to 1.2 is recommended for the main litchi production areas of China.