Combined effects of nitrogen and sulfur fertilization on maize growth, physiological traits, N and S uptake, and their diagnosis

A comprehensive understanding of the combined effects of nitrogen (N) and sulfur (S) on maize (Zea mays L.) helps to improve maize productivity. However, there is little consensus about the responses of maize to combined N and S application. Field and pot experiments were conducted to assess the effects of different N and S levels on grain yield, biomass, and N and S uptake. In addition, we determined the sufficiency range of N and S concentrations in different maize parts to decide whether N or S application is necessary. Field experiments consisted of different N and S treatments, and were conducted during 2011, 2012, 2015, and 2016. Pot experiments included 25 treatments, i.e., the factorial combinations of five N levels (0, 7.5, 15, 22.5, and 30 mM) and five S levels (0, 1, 2, 3, and 4 mM). Data in pot experiments were used to explain and validate the findings in field experiments. The results showed that N and S levels had significant interactions on grain yield (field experiments), biomass, N and S uptake, leaf area, leaf chlorophyll concentration, and root area (pot experiments). Leaf area, leaf chlorophyll concentration, and root area showed significant linear relationships with grain yield and biomass (field and pot experiments). There were synergies between N and S assimilation because glutamine synthetase contributed to S uptake, while ATP sulfurylase contributed to N uptake. Leaf N concentration and leaf N:S ratio together were suitable for determining whether N and S application is necessary. For >= 95% maximum relative yield (field experiments), the sufficiency range of leaf N was 25.9-29.3 mg N g(-1) while that of leaf N:S ratio was 16.3-19.6. Overall, maize yield, growth and physiological traits, and N and S uptake can be improved by adjusting application rates of N and S. Nitrogen concentration and the N:S ratio in leaves can be used to guide N and S management in maize production.