Does a hormonal plant growth promoter (KIN, GA(3), and IBA) affect grain yield and N, P, K, Ca, and Mg uptake in wheat crop in Southern Brazil?

Plant growth-promoting substances have been commercialized in agriculture, especially synthetic hormones such as kinetin (KIN), gibberellic acid (GA(3)), and indole-3-butyric acid (IBA). However, few studies proved the agronomic effect of these substances on the main crops. The objective of this work was to evaluate rates and methods of application of a hormonal plant growth promoter (HPGP -0.09 g L-1 KIN, 0.05 g L-1 GA(3), and 0.05 g L-1 IBA) and their effects on wheat grain yield and nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) uptake. The research was carried out in Londrina, Brazil. A randomized block design was implemented, considering a 2 x 3 x 4 factorial arrangement. It was composed of two genotypes (BRS Gralha-Azul and BRS Sanhaco), three HPGP rates (0, 5, and 10 mL kg(-1)) applied on the seeds, and four HPGP rates (0, 0.25, 0.5, and 1 L ha(-1)) sprayed on the leaves. Applications of HPGP did not change grain yield, density of fertile plants, lodging, plant height, aboveground dry matter (AGDM); P, Ca, and Mg concentration in the AGDM; and P, K, Ca, and Mg utilization efficiency (UE). In 2016, the application of 5 mL kg(-1) HPGP on the seeds (without HPGP on the leaves) increased by 20.9% the N concentration in the AGDM. In 2017, NUE increased up to 21.2% in response to HPGP sprayed on the leaves. The diversity of interactions among genotypes, HPGP application techniques, and weather conditions hinders the assertive use of the product by farmers.