Soil Carbon Fractions in Response to Long-Term Crop Rotations in the Loess Plateau of China.

Diversified crop rotations may enhance C fractions and soil quality by affecting the quality and quantity of crop residue returned to the soil compared with monocropping and fallow. We evaluated the effect of 30-yr-old diversified crop rotations on soil C fractions at 0- to 15- and 15- to 30-cm depths in the Loess Plateau of China. Crop rotations were continuous winter wheat (Triticum aestivum L.) (W); 3-yr rotations of corn (Zea mays L.)-winter wheat-winter wheat-millet (Eleusine coracana L.) (CWWM), pea (Pisum sativum L.)-winter wheat-winter wheat-millet (PWWM), and sainfoin (Onobrychis viciifolia Scop.)-winter wheat-winter wheat-sainfoin (SWWS); 4-yr rotation of pea-winter wheat-winter wheat-corn (PWWC); and 8-yr rotation of alfalfa (Medicago sativa L.) (4 yr)-potato (solanum tuberosum L.) (1 yr)-winter wheat (3 yr) (A4PoW3). A fallow (F) treatment was also included for comparison. Carbon fractions were soil organic C (SOC), particulate organic C (POC), potential C mineralization (PCM), and microbial biomass C (MBC). At both depths, SOC was greater in A4PoW3 than other crop rotations, except CWWM and PWWC. At 0 to 15 cm, POC was greater in CWWM and at 15 to 30 cm was greater in A4PoW3 than other crop rotations. At both depths, PCM was greater in CWWM and PWWC than F and W and MBC was greater in PWWC than other crop rotations. Carbon fractions increased with increased rotation lengths. Diversified crop rotations with increased residue production and longer year rotations enhanced soil C sequestration and microbial biomass and activity compared with monocropping and fallow.