Synergistic improvement of soil organic carbon storage and wheat grain zinc bioavailability by straw return in combination with Zn application on the Loess Plateau of China

Organic amendment can increase soil zinc (Zn) availability and its uptake in cereals. Conversely, Zn transformation in soil may modify soil organic carbon (SOC) dynamics. To date, the effects of the simultaneous addition of organic material and Zn fertilizer on soil SOC storage and crop Zn enrichment have received little attention. Here, with a view to clarifying this problem, a 2-year wheat-based field study was conducted on the Loess Plateau in China with the following treatments: control, SR alone (SR75, 7.5 Mg.ha(-1) ZF alone (ZF(15), 15 kg Zn.ha(-1)), and SR plus ZF (ZF(15)SR(7.5)). The results indicate that loss of SOC after 2 years was 0.6 Mg.ha(-1) in the control soil, and an input of 2.2 Mg C.ha(-1).y(-1) was needed to maintain the pre-experimental SOC stock. However, the increase in SOC storage after 2 years was 1.0 Mg.ha(-1) in soil with SR7 5 and 2.6 Mg.ha(-1 )in soil with ZF(15)SR(7.5), which accounted for 9.3% and 24% of residue-C input, respectively. On the other hand, the concentration of available Zn in soil with ZF15 was 3-fold higher than that in the control soil, but lower than that in soil with ZF(15)SR(7.5) in both years. The Zn uptake by wheat and the grain Zn concentration also increased as the soil Zn availability increased, especially in the second year. Most importantly, in soil with ZF(15)SR(7.5), the wheat grain Zn concentration reached 38 mg.kg(-1) after 2 years, and the estimated dietary-absorbed Zn was 3.65 mg.d(-1), which met the recommended Zn intake of 3 mg.d(-1) for adults. Therefore, combining SR and ZF shows a promising synergistic effect for the enhancement of both SOC storage and wheat grain Zn bioavailability on China's Loess Plateau and other drylands.