Response to Zinc in Maize Crops in the Argentinian Pampas

Grain crops grown in the Pampas region of Argentina, especially maize, often show Zn deficiencies. However, research on maize response to Zn fertilization is scarce. The objectives of this research project were to: 1) quantify maize responses to Zn fertilization in the Pampas region; 2) determine the optimum Zn application rate for maize; and 3) validate local Zn analyses and critical levels. Eighteen field experiments were carried out between 2009 and 2012 in early-season maize at different locations in the Pampas region. Visual deficiency symptoms of Zn were observed at most locations. Significant positive grain yield responses to Zn additions were observed at 12 of 18 sites. Average maize grain yields for the 18 experiments were 10.3, 10.5, 10.6, 10.8, and 10.7 t/ha for Zn application of 0, 0.5, 1, 1.5, and 2 kg Zn/ha, respectively. Optimum Zn rates varied between 1.0 and 2 kg Zn/ha, depending on the location. The average Zn response, when Zn was applied at 1.5 kg Zn/ha, was 4.7% (+487 kg/ha). No negative responses to Zn application were observed at any of the studied locations.

Ten additional experiments were carried out in the 2012/13 and 2013/14 growing seasons to evaluate Zn response in late-season maize crops. Experiments were located at southern Cordoba, southern Santa Fe, and western and northern Buenos Aires. Treatments included N, NP, NPS, and NPS with different Zn application rates (0.5, 1, 1.5, and 2 kg Zn/ha ). Fertilizer sources used were urea (N treatment), MAP + urea (NP treatment), MicroEssentials S10^TM (12-40-0-10S; NPS treatment), and MicroEssentials Zn^TM (12-40-0-10S-1Zn; NPS plus Zn treatments). Nitrogen, P and S rates used were 80 kg N/ha, 35 kg P/ha and 20 kg S/ha. Significant positive grain yield responses to Zn additions were observed at 4 of the 10 sites. On average, the application of 1.0 kg Zn/ha, significantly increased grain yield by 7% (660 kg/ha) and 4.4% (440 kg/ha) compared to the the N and NP treatments, respectively. Also, the treatment NPS + 1.0 kg Zn tended to increase grain yield by 1.3% (131 kg/ha) compared to the NPS treatment. At the responsive sites, Zn response could not be associated with parameters such as soil organic matter, pH and extractable Zn. Responses to N, P, S, and Zn in late-season maize indicate that these nutrients should be incorporated following the 4R principles of right rate, right time, right place, and right source; and that critical thresholds should be the same as those used for early-season maize.