Response of root growth and distribution of maize plants to foliar-sprayed antitranspirant and soil-amended hydrogel polymer

Root growth and development of maize (Zea mays L.) is an important process in determining grain yield. The effects of combined fulvic acid (FA, potassium humate as FA source) and super absorbent polymer (SAP) uses on maize root growth and yield were studied. A 2x3 factorial field experiment was applied by combining two SAP doses (0, 45 kg ha-1) and three FA rates (0, 1, and 2 g L-1) over 2 yr. Super absorbent polymer was applied to upper 20 cm soil layer at sowing, and FA solutions (1 or 2 g L-1, corresponding to FA1 and FA2) were sprayed onto the canopy three times during growing season. Root parameters, including root biomass, root length density (RLD), root surface-area density (RSD), and root diameter, were determined in the top 40 cm soil layer. Relative to control plants, both chemicals significantly increased root biomass, but these effects were not significantly different from their combined use. Compared to individual FA or SAP treatment, combined applications increased RLD and RSD in 0-20 cm depth. The combined SAP and FA2 improved RLD at 0-10 cm by 32% compared to FA2 treatment alone and by 82% compared to non-chemicals control plots over 2 yr. Averaged root diameters also significantly increased in the 40 cm soil layer in FA and SAP treatments alone compared to control, but they were not significantly different with the combined treatment. Similar patterns were found for maize yield each year. The combined application of SAP (45 kg ha-1) and FA2 (2 g L-1) greatly increased root length density and biomass than their individual application, and it could be suitable for high production of maize grown under low rainfall conditions.