Abstract
Drip irrigation is presently widely recognized as the most efficient irrigation system that can be used in woody perennial crops. However, uncertainties exist on the more appropriate agronomic design to employ. Here, we summarized the research carried out for three seasons in two young woody perennial crops (persimmon and lemon) in southeastern Spain. Several irrigation designs were compared by maintaining a similar amount of water application but varying the number of emitters and pipelines in each row in the orchard. In the lemon trial, the agronomic irrigation design was additionally combined with different irrigation regimes, comparing full irrigation (FI) with sustained deficit irrigation (SDI). In the persimmon trees, which were still at the juvenility stage, varying the number of emitters per tree or the number of drip lines per tree row, neither affects tree performance nor fruit yield in two out of the three seasons. However, over the entire experimental period, the relative trunk growth increased when more emitters were employed. In the lemon trial, carried out with trees that had reached commercial production, the FI, compared with SDI, increased trunk growth and average fruit weight, while a reduced number of fruits per tree without affecting total yield was observed in the third year of experimentation. The number of emitters per tree only had an effect the first year, increasing lemon fruit weight when the number of drippers per tree increased. In addition, fruit composition was not consistently affected by the irrigation design. It is concluded that, for a given irrigation dose, irrigation frequency, and soil conditions (loam-clay texture), in both very young and more mature trees, increasing the number of emitters or the wetted area only had some slight positive effects on tree performance.
Highlights
Drip irrigation is a water delivery technology that increases irrigation efficiency by decreasing soil evaporation and reducing the wetting of the soil surface when compared with other surface or solid sprinkler irrigation methods [1]
The agronomic irrigation design was combined with different irrigation regimes, comparing full irrigation (FI) with sustained deficit irrigation (SDI)
In a clay-based soil, if the irrigation system wets a large proportion of the soil system, direct evaporation from the soil may increase, when the wet soil surface areas are not shaded by the tree crown, thereby affecting the overall orchard water balance and irrigation efficiency [7]
Summary
Drip irrigation is a water delivery technology that increases irrigation efficiency by decreasing soil evaporation and reducing the wetting of the soil surface when compared with other surface or solid sprinkler irrigation methods [1]. Despite the widespread introduction of drip irrigation in the past 40 years and the general suggestions on the amount of the soil area to be wetted that is normally found in irrigation manuals [3], in woody perennial crops, there are still doubts about the optimum soil area to be wetted This important aspect, as well as the frequency of irrigation, should be considered, as the wetted soil area will affect the soil hydraulic conductivity, tree transpiration, and the possible water leaching due to deep percolation [4]. In this regard, soil texture plays an important role [5]; because of their increased infiltration rate, sandy soils will require a larger wetted surface, higher irrigation frequencies, and lower irrigation doses than heavy clay soils. On the other hand, when similar testing was carried out in a stonier soil with lower soil water holding capacity, the use of up to three drip lines per row of trees was preferred [9]
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