Effects of naphthalene acetic acid and phthalamic acid on the uptake and transfer of nutrients after anthesis in maize

  Objectives  We studied the effects of naphthalene acetic acid (NAA) and auxin inhibitor (NPA) on the uptake and transfer of nutrients after anthesis to provide technical ways for achieving improved maize efficiency.

  Methods  A field experiment was conducted with the maize cultivar of Zhengdan 958 (ZD958). NAA and NPA of 0.05, 0.1, and 0.5 mmol/L were sprayed on maize leaves at silking stage. The suitably applied concentration, determined by yield and nutrient transfer, was 0.05–0.1 mmol/L. A pot experiment was conducted to study the absorption and transfer of nutrients affected by NAA (0.1 mmol/L) and NPA (0.1 mmol/L), with clean water as the control. The maize was divided into two groups before silking. The first group’s female ears were covered with bags to prevent pollination, and the other group was allowed to undergo pollination. The mineral contents in different tissues at the silking and physiological maturity stages were determined.

  Results  Compared to the control, low concentration of NAA treatments (0.05 mmol/L and 0.1 mmol/L) significantly increased the grain yield, 100 grain weight and harvest index, which were increased by 14.3%, 14.2% and 8.9% in 0.1 mmol/L NAA treatment, respectively. Compared with NAA and NPA, source-sink relationship had a greater impact on the absorption and translocation of dry matter and nutrients. With the increase of source-sink ratio, the pre-silking nutrient translocation decreased and the pre-silking nutrient accumulation increased. The translocation and accumulation of P, K, Cu, and Mn were more sensitive to NAA and NPA. Compared to the control, NAA increased post-silking K and Mn contents in leaves by 25.6% and 90.4%, while NPA increased post-silking K content in stems and leaves by 56.4% and 65.9%, respectively. However, the contents of N, Mg, Zn, and Fe were less affected by NAA and NPA.

  Conclusions  NAA can improve maize yield and promote the transfer of nutrients to grains. NPA allows assimilates to accumulate in leaves and improve the source strength. Without grain formation, NPA enhances the growth of leaves, and improves mineral nutrition accumulation of whole plant. In practice, growth regulators can be used according to different production purposes to obtain maximum economic benefits.