Dynamics of Soil and Grain Micronutrients as Affected by Long-Term Fertilization in an Aquic Inceptisol

Micronutrient status in soils can be affected by long-term fertilization and intensive cropping. A 19-year experiment (1990–2008) was carried out to investigate the influence of different fertilization regimes on micronutrients in an Aquic Inceptisol and maize and wheat grains in Zhengzhou, China. The results showed that soil total Cu and Zn markedly declined after 19 years with application of N fertilizer alone. Soil total Fe and Mn were significantly increased mainly due to atmospheric deposition. Applications of P and organic fertilizer with incorporation of straws resulted in dramatic increases in soil total Cu, Zn, Fe, and Mn. Soil diethylenetriamine pentaacetic acid (DTPA)-extractable Cu in all treatments sharply decreased from initially 1.12 to about 0.8 mg kg−1. The treatments with organic fertilizer had the highest soil DTPA-extractable Cu, Zn, Fe, and Mn after 19 years of cropping and fertilization, thus demonstrating the important role of organic fertilizer application in improving available micronutrient status. Cu and Zn contents in wheat grains in the no-P treatments were significantly higher than those of the treatments with P application. In addition, Fe and Mn contents in wheat grains were positively correlated with their soil DTPA-extractable concentrations. These indicated that the long-term application of organic fertilizer resulted in significant increases in soil total and available micronutrient concentrations and remarkable reduction in wheat grain Cu and Zn contents, which was due to high soil available P.