Synthesis of calcium borate nanoparticles and its use as a potential foliar fertilizer in lettuce (Lactuca sativa) and zucchini (Cucurbita pepo)

This study was carried out to evaluate the effects of foliar sprays containing boron (B) nano-fertilizer (NF) on the growth and physiology of lettuce (Lactuca sativa) and zucchini (Cucurbita pepo). Plants were grown under greenhouse conditions for 60 days on a modified Hoagland solution with the presence and absence of boron (+B or –B). A synthesized B–NF foliar spray and a commercial B foliar fertilizer (Bortrac™ 150, BT) was applied at a concentration of 30 mg B L−1 at 10-d intervals throughout the experiment. The B–NF treatment increased the growth of lettuce 2.7- and 1.9-fold for shoots and roots, respectively, with an average production of lettuce biomass by ~58%. Similarly, the NF increased the growth of zucchini by 18 and 66% compared with Control–B (the absence of B), and 13 and 36% compared with BT, both for shoots and roots, respectively. Nevertheless, NF + B mostly decreased lettuce growth with symptoms of B toxicity in leaves. In lettuce, addition of B did not affect concentrations of phenols; however, in zucchini, Control–B induced a higher production of phenolic compounds possibly related to B deficiency. The B addition in lettuce reduced the DPPH activity by 32 and 21% in NF and BT, respectively, compared to Control-B. These responses were similar in zucchini; however, the effect of B was product of its presence in mineral solution rather than due the foliar product applied. This suggests that a NF-based delivery system for B may be highly effective at boosting plant productivity on B-limited soils.