Zinc fertilization strategies in soybean: plant uptake, yield, and seed concentration

Based on the expected increase in soybean (Glycine max L.) demand and the current yield gap, smart management strategies of crop nutrition are required to improve the use of resources. Given that zinc (Zn) deficiency is the most widespread micronutrient problem in agricultural production systems, the objective of this study was to evaluate, under field conditions, the effect of different Zn fertilization strategies on seed yield, Zn uptake, and seed Zn concentration in Zn-deficient soils. To this end, a field experiment was conducted at three sites evaluating the following treatments: (i) Control=no Zn application; (ii) Seed-Zn=Zn applied to the seed (0.3kg ha(-1)); (iii) Foliar-Zn=Zn foliar-applied at V-5 (0.7kg ha(-1)); and (iv) Soil-Zn=Zn applied to the soil at sowing (2.1kg ha(-1)). At all sites, Zn fertilization significantly (p<0.05) increased seed yield (9.5%) regardless of the fertilization strategy. The Foliar- and Soil-Zn applications generated the greatest leaf Zn concentration at R-5.5 stage (60 and 50mg kg(-1), respectively). Zinc concentration in stems, pods, and the whole plant did not differ between treatments (avg. 12, 41, and 31mg kg(-1), respectively). Only Soil-Zn application increased seed Zn concentration compared to the unfertilized Control (11%). Future research on Zn dynamic in soybean should focus on: (i) recalibrating thresholds based on leaf and seed Zn concentration and (ii) evaluating different times, sources, and rates of Foliar-Zn application in reproductive stages, alone or in combination with Soil-Zn applications, to reach Zn biofortification.