The principle of chemical fertilizer application for lemon trees is to apply deep autumn fertilizer and fruit picking fertilizer, and to see that trees are supplemented with pre flower fertilizer and ear fruit fertilizer, so as to make the first half young and the second half heavy.

During the spring shoot sprouting from February to March, the first fertilization was carried out. According to the strength of the tree, some available nitrogen fertilizer was applied respectively. The trees with more weak wood and flowers should be applied more properly; the trees with strong wood and less flowers should be applied less or not. The amount of nitrogen fertilizer accounted for 10-15% of the total amount of the whole year, promoting the healthy growth of spring flowers.

In the second fertilization, 0.3% urea solution was sprayed for many times after flower withering and before fruit expansion, combined with fruit conservation and insect control, to timely supplement the loss of tree nutrients after flowering and increase the fruit bearing capacity.

The third time of fertilization was from July to August, which was in the period of shoot sprouting and fruit expanding. This time, the amount of fertilizer application was large. Nitrogen fertilizer accounted for 40% of the annual amount, and phosphorus and potassium fertilizer accounted for 50% respectively. Two fertilizer pits were opened at each drip line, 30-40 cm deep, to ensure that the mother branches of autumn shoots were strong and the spring flowers were well differentiated.

For the fourth time, after fruit picking in November and before the temperature drops, the deep fertilization should be applied again. In the other two sides of autumn fertilization, the deep excavation pit, the amount of nitrogen fertilizer application accounts for 40% of the annual amount, phosphorus, potassium fertilizer accounts for 40%, mainly green fertilizer, slag fertilizer and other organic slow effect fertilizer.

The amount of fertilizer application is determined according to the yield of each tree in recent two years. Based on the yield of 30 kg per year, 0.3 kg of pure nitrogen, 0.2 kg of pure phosphorus, 0.2 kg of pure potassium, about 0.6 kg of urea, 1.0 kg of superphosphate and 0.5 kg of potassium chloride should be applied to each tree. According to the experiment, for 15 year old lemon tree, milk cow manure is applied 4 times a year, each plant is 150 kg, and the average plant yield is 48 kg; each plant is applied 50O kg, and the plant yield can reach 73 kg.