Table 4 Long-term fertilization experiment and the amount of applied fertilizers.

From: Impacts of Long-term Fertilization on the Molecular Structure of Humic Acid and Organic Carbon Content in Soil Aggregates in Black Soil

Treatment

N (kg·ha−1 y−1)

P2O5 (kg·ha−1 y−1)

K2O (kg·ha−1 y−1)

Horse manure (t·ha−1)

Wheat

Soybean

Maize

Wheat

Soybean

Maize

CK

0

0

0

0

0

0

0

0

NPK

150

75

150

75

150

75

75

0

M

0

0

0

0

0

0

0

18.6

MNPK

150

75

150

75

150

75

75

18.6

  1. CK, no fertilizer treatment; NPK, chemical NPK fertilizers; M, organic manure treatment; MNPK, treatment of organic manure combined with chemical NPK fertilizers.
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