Aims The aim of this study was to investigate the proofof-concept that Andean potato (Solanum tuberosum L., Andigenum Group) can be agronomically biofortified with iron (Fe) and zinc (Zn) fertilizers. Methods Greenhouse and field experiments were conducted in the Ecuadorian Andes with varying rates of foliar and soil applied Fe and Zn fertilizers to investigate the potential resulting increase in tuber Fe and tuber Zn concentrations.Results The study showed that simple fertilizer practices enhancing Zn supply to potato plants can increase tuber Zn concentrations. The rate of increase of tuber Zn following Zn fertilization was similar across cultivars. A concomitant negative effect of high rates of Zn applications on yield was not seen, and a maximum Zn application level for increasing tuber Zn concentration was not identified. A positive tuber yield effect was seen at one field site. High rates of foliar Zn application reached a 2.51-fold tuber Zn increase, and high rates of soil Zn application a 1.91-fold tuber Zn increase. The experiments showed no positive correlation between Fe fertilization and Fe concentration in tubers. Moreover, the study showed a strong effect of site on the concentration of Fe and Zn in tubers, and the tuber mineral concentrations across sites and treatments were negatively correlated with tuber yield. Conclusions The results confirmed the proof of concept that Andean potato cultivars can be agronomically Znbiofortified with foliar and soil applied Zn fertilizers. Tuber Fe concentrations of Andean potatoes were not increased with Fe fertilization.

Biological activities determine quality, sustainability, health, and fertility of soils. The purpose of this study was to evaluate chemical and biological characteristics of soils from Ecuadorian highlands subjected to different management practices, as well as the density and diversity of arbuscular mycorrhizal fungi (AMF). Soils from naturalized grasslands and other previously cropped plots with Zea mays and Solanum tuberosum were analyzed in laboratory for soil biochemical properties, enzyme activity, and AMF colonization to determine the effect of the soil management over its quality. The characterization of AMF propagules associated to spontaneously colonizing plants in the above soils was also performed. Soil previously cropped with S. tuberosum showed the highest glomalin content; at the same time, naturalized grassland and Z. mays cropped soils showed higher hyphal length. The acid phosphatase activity was higher in naturalized grasslands and Z. mays cropped soils compared with that in the S. tuberosum cropped soils. Moreover, the highest AMF colonization rates and spore number were found in different spontaneous plant species growing in the naturalized grasslands. This study represents the first characterization of AMF propagules of different cropped and naturalized grassland soils, and also is one of the first reports about changes on biochemical and microbial activities occurring in Andean soils from the highlands of Ecuador, undergoing determinant soil management activities.

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