A Prediction Model of Forest Preliminary Precision Fertilization Based on Improved GRA-PSO-BP Neural Network

Table 1

Test results of physical and chemical properties of the soil of experimental forest land.

Stand age (t/a)	Site index S	Texture	Organic matter (g/kg^−1)	Total nitrogen (g/kg^−1)	Fast-acting nitrogen (mg/kg^−1)	Fast-acting phosphorus (g/kg^−1)	Fast-acting potassium (g/kg^−1)	PH
5a	5	Middle soil	9.0	0.3	16	2.1	57	4.6
	18	Middle soil	17.4	0.89	27.7	3.0	80	4.9
	21	Middle soil	22.0	1.12	32	4.0	92	5.0
	23	Middle soil	27.0	1.35	48	5.0	100	5.2
19a	5	Middle soil	8.9	0.32	16.4	2.3	54	4.5
	18	Middle soil	17.2	0.9	28	3.1	88	4.8
	21	Middle soil	22.1	1.14	32	4.1	90	5.1
	23	Middle soil	27.3	1.38	47.6	5.0	96	5.3
22a	5	Middle soil	9.0	0.31	16.1	2.2	52	4.4
	18	Middle soil	17.1	0.87	28.1	3.2	91	4.7
	21	Middle soil	22.0	1.11	32	4.2	87	5.4
	23	Middle soil	27.1	1.33	48.1	5.2	94	5.1
25a	5	Middle soil	9.1	0.3	16.2	2.0	55	4.8
	18	Middle soil	17.3	0.91	28.2	3.0	83	4.9
	21	Middle soil	22.2	1.10	32	4.3	91	5.3
	23	Middle soil	27.0	1.36	47.9	5.1	100	5.1