(1) Soil rhizosphere fertilization
Citrus is a deep-rooted crop, and its roots are mainly distributed in the depth of about 60 cm, and more roots are distributed in the depth of 15 ~ 40 cm. The location of fertilization should be in the soil under the drip line outside the canopy, because the absorption roots are distributed in the soil outside the canopy. Pay attention to the symmetrical rotation of fertilization locations in the east, west, north and south. Fertilization is generally applied to the depth of 15 ~ 40 cm, and with the expansion of the crown, the fertilization holes will gradually move outward.
① Fertilization method: young trees dig annular ditches for fertilization, adult fruit trees dig strip ditches for fertilization, and fruit trees with narrow terraces dig radial ditches for fertilization. Trench depth: topdressing should be shallow, digging10 ~ 20 cm; The base fertilizer should be deep, digging 30 ~ 40 cm. The width of the ditch is 30 ~ 40cm, and the length depends on the crown size, generally about1m. The bottom of the ditch should be flat. Fertilizer should be applied to the ditch, and the soil should be covered after it is drained.
② Mixed application of organic fertilizer and chemical fertilizer: mixed application of organic fertilizer and chemical fertilizer, combining fertilizer efficiency and giving full play to fertilizer efficiency. At the same time, humus produced by organic matter decomposition has the ability to adsorb ammonium, potassium, magnesium, calcium and iron ions, which can reduce the loss of chemical fertilizer. In particular, nitrogen fertilizer should be mixed with organic fertilizer for deep application, so that root groups can be easily absorbed and soil fixation or loss can be prevented.
Applying a large amount of organic fertilizer in orchard can improve soil physical properties, improve soil fertility and deep soil structure, which is beneficial to root growth and is not easy to cause element deficiency. In the season when plants grow vigorously, there is a high demand for nutrition. Chemical fertilizer can be used as topdressing to provide nutrients needed by plants in time to ensure the normal growth and development of citrus.
Soil fertilization should be mastered flexibly according to the specific situation, and it is not suitable to fertilize before rain or during heavy rain. After the rain, Chu Qing should seize the time to fertilize; Dry fertilization in rainy season, irrigation and fertilization in dry season or irrigation immediately after fertilization. Sandy soil has poor ability to retain fertilizer and water, and fertilization in Qin Ying is thin and shallow; Clay soil can be fertilized again, the depth should be combined, and the surface soil should be kept loose; Chemical fertilizer should be applied deeply in red soil mountainous area. Strip application or furrow application can not only improve the soil, but also make the root system develop deeper, which is beneficial to drought resistance and cold resistance. At the peak of citrus rooting (usually in June-July), nitrogen fertilizer can be applied shallowly in combination with promoting root development, but if it is applied deeply at this time, it will cause excessive cutting and burning of new roots. Because nitrogen is easy to be lost after being applied to soil, nitrogen fertilizer should be applied to the main distribution depth of citrus root system, and the dosage should not be too much at a time.
(2) Topdressing outside the roots
If the citrus lacks trace elements and the root system grows poorly, resulting in wilting leaves, weak tree vigor, flower protection and fruit protection, and too many fruits, temporary fertilization can be used to supplement the deficiency of root topdressing. According to the nutritional needs of citrus in different growth stages, soil fertilization is the main method, and topdressing is applied outside the roots. According to local experience, topdressing outside the root is summarized as follows.
Spraying the mixture of 0.5% urea, 2% calcium superphosphate and 2% potassium sulfate before flowering can improve the flowering and seed setting rate. Spraying 0. 1% boric acid or borax mixed with 0.3% ~ 0.4% urea or spraying 1% ~ 2% calcium superphosphate mixed with10 mg/kg 2,4-d solution at flowering stage can make the flowers bear good fruits. Spraying 0.4% ~ 0.5% urea and 0.2% ~ 0.3% potassium dihydrogen phosphate can reduce the abscission of young fruits and improve the fruit setting rate when the leaves turn green after flowering in spring. Spraying 0.3% urea, 3% calcium superphosphate and 0.5% ~ 1% potassium sulfate can promote the growth of young fruits. You can also spray 2% lime water to reduce fruit sunburn and increase calcium. Spraying 1 ~ 2 days and 1 day with 2 ~ 3 times of 1% ~ 2% calcium superphosphate extract and 1 time before fruit harvesting can reduce citric acid content, increase sugar content and improve quality. Spraying 0.3% ~ 0.5% potassium dihydrogen phosphate or 3% calcium superphosphate in winter can promote the formation of flower buds and increase the number of flowers. Young trees can be sprayed with 0.3% urea after each budding. After nitrogen supply to roots was stopped in August, 2% ~ 3% calcium superphosphate was sprayed, and 2% potassium sulfate or 3% ~ 5% plant ash was added to promote the growth and enrichment of branches and store nutrients for early fruits in the coming year.
Practice has proved that spraying auxin at the same time of topdressing outside the roots can achieve better effect of flower and fruit protection. Combined with topdressing outside roots, spraying 2,4-d or 50 ~ 100mg/kg NAA twice in young fruit stage in Fujian can increase the fruit setting rate 1.94% ~ 14.07%. Spraying10 ~ 20 mg/kg of 2,4-d solution for 3 times during the fruit expansion period increased the fruit diameter by 0.44cm ... When 3/4 of Wenzhou tangerine in Hubei died, spraying 50 mg/kg of "920" increased the fruit setting rate by 4 times. Spraying 0.5% urea and 5 ~10mg/kg 2,4-d at the flowering stage in Chongqing, Sichuan, spraying 0.2% urea and 15 ~ 20mg/kg 2,4-d and15 ~ 20 days at the flower bud differentiation stage in Jincheng, and spraying in Sichuan for 400 days. Therefore, for citrus orchards with abnormal growth and large and small years, 200 ~ 600 mg/kg of "920" should be sprayed at the peak of flower bud differentiation in the new year to inhibit flower bud differentiation; Spraying 50 ~ 100 mg/kg of "920" after flowers wither in early years can improve the fruit setting rate, thus achieving certain results in overcoming the big and small years.
The proper concentration and dosage of topdressing outside the roots and spraying auxin should be mastered. Too high concentration will cause fertilizer (medicine) harm or other side effects, and too low concentration will have poor effect. See Table 9-6 for the concentrations of fertilizers and auxin currently used in production.
Table 9-6 Fertilizer and auxin concentration used
Table 9-6 Concentration of Fertilizer and Auxin (Continued)-1