Abstract
The increase in the demand for almonds, the development of novel self-fertile and late-flowering varieties, and the establishment of plantations in new irrigated areas have led to significant progress in the productive techniques of almond tree cultivation. One of the most important has been the increase in planting density, due to the development of dwarfing rootstocks. This paper presents a comparison between two training systems with ‘Soleta’ almond cultivar: a super high density (SHD) system using Rootpac-20 dwarfing rootstock versus an open-center training system using GF-677 rootstock. To this end, several parameters related to chlorophyll content (fluorescence and SPAD) and light interception (from photosynthetically active radiation (PAR) measurements) were monitored throughout two vegetative cycles, and other productive conditions (flowering, fruit set and production) were tracked at specific times of the cycle. The open-center system resulted in higher PAR interception than the SHD system, but also in the presence of poorly illuminated fractions of the canopy. Differences were observed between both systems in terms of average fruit weight and yield per canopy volume. Lower yields were obtained in SHD system than in open-center, which may be significantly increased by adapting the inter-row spacing. However, the degree of efficiency in the use of resources or productive inputs, such as irrigation, was favorable to the new SHD training system, so its potential to become a reference system in modern plantations (using over-the-row harvesters similar to those used for vine and olive trees) seems promising.
Highlights
The USA, and California, leads the world production of almonds, with an 80%market share
Fv/Fm values, which provide an estimation of the maximum quantum efficiency of PSII photochemistry, were indicative of the absence of environmental stress in the trees efficiency of PSII photochemistry, were indicative of the absence of environmental stress in the trees (Fv/Fm > 0.8) in all cases and in both growing seasons (2018 and 2019), and were similar to those (Fv/Fm > 0.8) in all cases and in both growing seasons (2018 and 2019), and were similar to those reported by Ranjbarfordoei et al [36]
This would be in agreement with Ben Yahmed et al [39], who found that the use of low vigor rootstocks could be associated to a higher yield efficiency, widely reported in deciduous fruit species. This higher efficiency is important for the future evolution of the super high density (SHD) system, since it indicates a more efficient use of light, with less shaded areas in the tree and with a canopy volume that is more quickly reached. Both seasonal and cumulative yield of kernel per ha were consistently higher in the open-center than in the SHD system (2) because the spacing was close to the optimum in the case of the open-center/GF-677 but not in the SHD/Rootpac-20, as we described below
Summary
The USA, and California, leads the world production of almonds, with an 80%market share. As far as crop area is concerned, the European Union concentrates 39% of the world almond-tree dedicated area, 84% of which is located in Spain, which accounts for almost one third of the world area [1]. In just a few years, in Spain the almond industry has gone from being a marginal crop grown in poor and arid soils to represent an alternative production to the traditional ones of deciduous fruit, cereals or citrus. This change in production management has caused the almond tree to currently offer a 20–25% higher profitability than cereals or olive trees for the same farm [3]. Almond consumption has markedly increased, as world demand has grown at a rate of 5% per year [3]
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