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-, 15-to 30-, and 0-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 wheatwinter 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 all depths, SOC and POC were greater in A4PoW3 than F, W, and PWWC. The PCM and MBC were greater with SWWS than most other crops rotations. Soil C fractions increased linearly with increased belowground crop residue returned to the soil. Both SOC and POC increased linearly with increased rotation length. All C fractions were also correlated with mean annualized crop grain yield. Diversified crop rotations with increased belowground residue production enhanced soil C sequestration and microbial biomass and activity as well as crop yield compared with monocropping.