Mapping Zinc in Soils from Brazil: Spatial Variability and Factors Influencing Zn Availability.

Maps of zinc (Zn) availability are important tools for adequate Zn recommendation in agriculture and for strategic planning of zinc demand by crops in Zn-deficient areas. This work aims to map zinc availability, as well as to present data on factors that influence Zn phytoavailability in Brazilian soils (soil pH, available phosphorus, clay content). We focused on samples of the Cerrado (nearly 110 million hectares, represented by ~ 38,000 soils samples), which is an important biome with a representative agricultural area and great importance in terms of agriculture output in Brazil. Data comprising soil fertility levels (Zn, P, pH) and texture (clay percent) were first plotted individually. For a better understanding of Zn phytoavailability, data on soil Zn (Mehlich-I extractable) were next interpolated with pH, clay, and available P (Zn vs pH; Zn vs Clay and Zn vs P_available). It is evident from our results that great attention should be given to Zn recommendation for adequate yields, as nearly 1/3 of the studied area presented low Zn levels (Zn_Mehlich < 1.6 mg dm^-3) and many have also high P, pH, and clay content, which might cause further decrease in soil-Zn availability. Considering our estimate of Zn deficiency and the most recent information provided by the Systematic Survey of Agricultural Production for the 2014/2015 season in Brazil, an estimation of soil Zn deficiency in areas cultivated with corn, sugarcane, wheat, soybean, and rice in Brazil would result in ~ 21.0 million hectares.  Additional data on available soil-Zn in agricultural frontiers, associated with information on better soil management practices is required to identify the factors that could limit Zn availability in the soils.