Boron (B) fertilizers are recognized as essential for ensuring yield and fruit quality. However,
the importance of soil and foliar B fertilization in almond orchards under rainfed conditions is
presently unclear. To address this literature gap, in the present study, the impact of soil and foliar
application of B on leaf gas exchange, leaf photosynthetic pigments, yield, and fruit quality in
almonds was investigated across three consecutive growing seasons. Boron fertilizer was applied to
the soil at four rates (0, 1, 2, and 3 kg ha−1) in the presence or absence of foliar application (0.36 g L−1)
of the same micronutrient. Borax pentahydrate was used as the B source. When compared to foliar
B fertilization, the soil application of B positively affected the gas exchange parameters, mainly
the net CO2 assimilation rate, stomatal conductance, and transpiration rate (percentage of gain
between 15% and 80%), but did not influence the chlorophyll content. The almond yield and fruit
characteristics were also enhanced (about 25–72%) in response to lower soil B fertilization rates. In
the 3 kg ha−1 dose, B had an adverse effect on the yield and resulted in lighter fruits. On the other
hand, foliar B fertilization did not benefit any of the evaluated parameters. Overall, these results
suggest that, under the studied conditions, almond orchards do not respond to higher B rates in soil
or foliar B fertilization.
This research work was funded by the project “Estratégias integradas para o aumento da
produtividade da amendoeira em Trás-os-Montes”, no. 54611, funded by the EAFRD (European
Agricultural Fund for Rural Development), and by the Portuguese State through the “Medida
4.1. Cooperação para a Inovação do programa PRODER-Programa de Desenvolvimento Rural”.
The authors also acknowledge to the Foundation for Science and Technology (FCT, Portugal) and
FEDER under Programme PT2020 for financial support to CIMO (UIDB/00690/2020) and CITAB
(UIDB/04033/2020).
