**5. Characteristics and difficulties of fertilization in forest land**

Forest land soil is the soil under forest cover, which is one of the organic components of forest ecosystem. Compared with conventional farmland and other uses of soil, forest land soil has special characteristics because of the impact of forest litter, woody plant root group, forest biological community, and special environmental conditions of forest ecosystem.

#### **5.1 Characteristics of forest fertilizer demand**

The regular pattern and absorptive capacity of forest trees are obviously different from that of most crops, with deep root, large root range, and low nutrition demand; most trees are perennial, immobile, and non-intercropped, with longterm and continuous nutrient supply; the growth cycle of general trees is long, with complex influencing factors and difficult nutrition diagnosis; moreover, the growth and development law of different trees is different [79].

#### **5.2 Fertilization requirements for forest land**

The fertilization in forest land is mainly based on base fertilizer, supplemented by top dressing; the spacing between plants and rows is large, and hole fertilization is often used, so it is difficult to apply fertilizer in mountainous area, and the times of fertilization are not many; the time, method, and amount of fertilization vary according to the characteristics of tree species [25].

#### **5.3 Difficulties in forest land fertilization**

The spatial heterogeneity of forest land nutrients is large, and the difficulty of nutrient diagnosis is large. The growth cycle of forest trees is long, the effect is slow, and the short-term fertilizer effect is not necessarily obvious. The spacing between trees and rows is large; there are many weeds in the forest, which need to be applied in caves; and the workload is large. The trees grow in mountainous areas, but the transportation conditions in mountainous areas are poor, so the cost of fertilization is high. The research on forest fertilization is also relatively late, and the nutrient characteristics of most trees are unknown. The method of fertilization is still in its infancy; at present, there are few special fertilizers for trees in the market [80].
