Table 1.

Basic information of the research area described in the paper.

Region	Type of fertilization	Type of soil
Heilongjiang	NP, PK, NPK, O, NPO, NPKO	Black soil
Jilin	N, NP, NK, PK, NPK, O, NO, NPKO	Black soil
Liaoning	NPK, NPKO	Black soil
Inner Mongolia	NP, NK, PK, NPK	Chestnut soil
Beijing	N, NP, NK, PK, NPK, NPKO	Fluvo-aquic soil, cinnamon soil
Tianjin	NP, NK, PK, NPK	Fluvo-aquic soil
Hebei	NP, NK, PK, NPK, NPKO	Fluvo-aquic soil, cinnamon soil, brown soil
Henan	N, NP, NK, NPK, NPKO	Fluvo-aquic soil, brown soil
Anhui	NPK	Fluvo-aquic soil
Shandong	NP, NK, PK, NPK, O, NPKO	Black soil, fluvo-aquic soil, brown soil
Shanxi	N, NP, NPK, O, NO, NPO, NPKO	Cinnamon soil
Gansu	N, NP, NK, PK, NPK, O, NO, NPO, NPKO	Fluvo-aquic soil, cinnamon soil, chestnut soil, lithologic soil, desert soil
Shaanxi	NP, NK, PK, NPK	Fluvo-aquic soil, cinnamon soil
Ningxia	NP, NK, PK, NPK	Lithologic soil
Xinjiang	PK, NPK, NPKO	Desert soil

N nitrogen fertilizer, NP combined application of nitrogen and phosphate fertilizer, NK nitrogen and potassium fertilizer combination, PK combined application of phosphate and potassium fertilizer, NPK combined application of nitrogen, phosphorus and potassium fertilizer, O organic fertilizer, NO organic fertilizer with nitrogen fertilizer, NPO organic fertilizer with nitrogen and phosphate fertilizer, NPKO organic fertilizer with NPK fertilizer.