Grain yield trends and changes in Soil Organic Carbon (SOC) from a 26-yr rainfed fertilization trial in Pingliang, Gansu, China, were recorded. Mean wheat ( Triticum aestivum L.) yields for the 18-yr ranged from 1.72 t ha -1 for the unfertilized plots (CK) to 4.65 t ha -1 for the plots that received Manure (M) annually with inorganic Nitrogen (N) and Phosphorus (P) fertilizers (MNP). Corn ( Zea mays L.) yields for the 6-yr averaged 2.43 and 5.35 t ha -1 in the same treatments. Yields declined with year except the CK for wheat. Wheat yields for the N only declined 117.8 kg ha -1 yr -1 that was the highest among all treatments and that for the NP declined 84.7 kg ha -1 yr -1, similar to that of 77.4 kg ha -1 yr -1 for the treatment receiving straw and N annually and P every second year (SNP). Likewise, the corn yields declined highly for all treatments and the declined amounts ranged from 108 to 258 kg ha -1 yr -1 that was much higher than in wheat. SOC gradually increased with time except the CK and N treatments, in which SOC remained almost stable. The SOC increases of 190.1, 166.8 and 164.5 mg C kg -1 yr -1 occurred in MNP and SNP and M treated soils, respectively. About 24% of the total C-input from manure and root residue and about 14% of the total C-input from straw and root residue remained in the soil as organic matter. Losses of 1 t SOM ha -1 were associated with a decrease in wheat yield of approximately 80 kg ha -1, showing the importance of using management practices that minimize losses of SOC in the China Loess Plateau. Grain yield declines were likely related to gradual dry weather and soil available N decline. It is concluded that C sequestration can be enhanced by increasing manure and straw additions in these dryland soils.
