Effect of Different Organic and Inorganic Fertilization Regimes on Soil Organic Carbon Pools in Soil Profiles of a Corn-Soybean Rotation.

Soil organic carbon (SOC) dynamics plays an important role in soil fertility and mitigation of climate change through carbon (C) sequestration in soils. Nutrient sources, such as manure, mineral fertilizers and straw, affect the quantity and quality of organic materials in soils and hence the amount of C sequestered. Currently, there is increasing interest of P-based on manure application in order to minimize the effect of organic fertilizer on water quality. However, the impact of these fertilization regimes on soil carbon pool dynamics is not well known. The objectives of this study were to investigate the effects of long-term inorganic and manure applications on SOC pools and total nitrogen (TN) under a corn-soybean rotation in temperate climate. Soil profile samples (0-7.5, 7.5-15, 15-30, 30-50, 50-70 cm) were collected from an established long-term experiment since 2004, which consists of six treatments: a zero-nutrient control (CK), nitrogen and potassium only (NK), chemical fertilizer P (CF), solid swine manure (SM), liquid swine manure (LM) and swine manure compost (MC). All organic and chemical P fertilization were based on 100 kg P₂O₅ ha^-1year^-1 except for CK and NK from 2004 to 2012. Total SOC and different extractable carbon were determined using a combustion C/N analyzer. The results showed that the SOC, water extractable C (WEC), and TN concentrations decreased with increasing the depths with major difference at 0-7.5 cm depth among different fertilization treatments. The concentration of SOC and WEC at 0-7.5 cm depth was increased by 18.8% and 31.9%, by 50.6% and 65.5% under SM as compared to that under CK and NK treatment, respectively. There was no statistically not significant between all treatments below soil profiles 7.5 cm except that CF also showed significant C in the layer 30-50 cm. Total soil N concentration followed the order of SM≈IP＞LM≈MC＞CK≈NK. These results indicate that long-term additions of solid swine manure have the most beneficial effects in building C pools among the investigated fertilization regimes.