A reasonable and efficient rotation sequences were established to solve the problem of replanting obstacles caused by continuous cropping of crops via determining the level of soil nutrient immobilization and residue under annually fallowing and seasonally planting different crops. The nutrients contents of 0-20 cm black flax soil under fallowing

and planting spring wheat

potato

Mongolian astragalus and Angelica sinensis were investigated. The field trial was followed by the single-factor randomized block design in Zhanpo village

Lianfeng town

Weiyuan

Gansu in 2018 and soils were sampled by "S" shape. The results showed that the contents of organic matter

total nitrogen

available phosphorus

available potassium

total anion and anion

Mg2+

SO42- and Cl- in 0-20 cm soil layer respectively were increased for annually fallowing and seasonally planting Mongolian astragalus. however

the contents of organic matter

total nitrogen

available phosphorus

available potassium

total amount of ions and ions

Mg2+

SO42- and Cl- in 0-20 cm soil layer were decreased for annually planting Angelica sinensis. The variance analysis showed that the contents of organic matter

total nitrogen

available phosphorus

available potassium

total anion

Mg2+

SO42- and Cl- in 0-20 cm soil layer were significantly higher for annually fallowing and seasonally planting Mongolian astragalus than those for seasonally planting Angelica sinensis. The principal component regression analysis showed that the soil fertility composite index scores respectively were up to 0.98 and 0.56 for annually fallowing and seasonally planting Mongolian astragalus

while the soil fertility composite index score was down to 0.07 for seasonally planting Angelica sinensis. This demonstrated that annually fallowing was a simple and effective method for combination of land utilization and maintenance in black flax soil

while seasonally planting Mongolian astragalus was an effective rotation sequence to improve soil fertility in black flax soil.