Long-term fertilization impacts on corn yields and soil organic matter on a clay-loam soil in Northeast China

A long-term fertilization experiment with monoculture corn (Zea mays L.) was established in 1980 on a clay-loam soil (Black Soil in Chinese Soil Classification and Typic Halpudoll in USDA Soil Taxonomy) at Gongzhuling, Jilin Province, China. The experiment aimed to study the sustainability of grain-corn production on this soil type with eight different nitrogen (N)-, phosphorus (P)-, and potassium (K)-mineral fertilizer combinations and three levels (0, 30, and 60 Mg ha(-1) y(-1)) of farmyard manure (FYM). On average, FYM additions produced higher grain yields (7.78 and 8.03 Mg ha(-1)) compared to the FYM0 (no farmyard application) treatments (5.67 Mg ha(-1)). The application of N fertilizer (solely or in various combinations with P and K) in the FYM0 treatment resulted in substantial grain-yield increases compared to the FYM0 control treatment (3.56 Mg ha(-1)). However, the use of NP or NK did not yield in any significant additional effect on the corn yield compared to the use of N alone. The treatments involving P, K, and PK fertilizers resulted in an average 24% increase in yield over the FYM0 control. Over all FYM treatments, the effect of fertilization on corn yield was NPK > NP = NK = N > PK = P > K = control. Farmyard-manure additions for 25 y increased soil organic-matter (SOM) content by 3.8 gkg(-1) (13.6%) in the FYM1 treatments and by 7.8 g kg(-1) (27.8%) in the FYM2 treatments, compared to a 3.2 g kg(-1) decrease (11.4%) in the FYM0 treatments. Overall, the results suggest that mineral fertilizers can maintain high yields, but a combination of mineral fertilizers plus farmyard manure are needed to enhance soil organic-matter levels in this soil type.