Abstract
Quantification of actual plant consumption of nitrogen (N) is necessary to optimize fertilization efficiency and minimize contamination of earth resources. We examined the performance of fruit-bearing pomegranate trees grown in soilless media and exposed to eight N-fertigation treatments, from 5 to 200 mg N L−1. Reproductive and vegetative indices were found to be optimal when 20 to 70 mg N L−1 was supplied. Nitrogen application levels over 70 mg L−1 reduced pomegranate development and reproduction. N uptake in low-level treatments was almost 100% and decreased gradually, down to 13% in 200 mg N L−1 treatment. N usage efficiency was maximized under 20 mg N L−1, in which case 80% to 90% of added N was taken up by the trees. At high N application, its efficiency was reduced with less than 50% utilized by the trees. Leaf N increased to a plateau as a function of increasing irrigation solution N, maximizing at ~15 to 20 mg N g−1. Therefore, analysis of diagnostic leaves is not a valid method to identify excessive detrimental N. The results should be valuable in the development of efficient, sustainable, environmentally responsible protocols for N fertilization in commercial pomegranate orchards, following adaptation and validation to real soil field conditions.
Highlights
Nitrogen (N) is a major nutritional element in plants, required in many physiological and developmental processes such as photosynthesis [1], metabolite biosynthesis [2,3] and flowering [4].Most N uptake in fruit trees occurs during the intensive vegetative growth and post-harvest phases [5].Diagnostic leaves, which are commonly used for nutritional status evaluation of fruit trees [6,7,8], are sampled following this seasonal pattern
Our work revealed that N is essential for pomegranate development, but when considering vegetative and reproductive indices, there is a point from which elevated N restrained tree development
Low N resulted in small, light-green blades, while in the excessive N treatments, the leaves were larger and darker (Figure 2). This finding is in line with the literature, as N deficiency in pomegranate is known to cause leaf yellowing and reduction in shoot growth and yield [28]
Summary
Nitrogen (N) is a major nutritional element in plants, required in many physiological and developmental processes such as photosynthesis [1], metabolite biosynthesis [2,3] and flowering [4]. Diagnostic leaves, which are commonly used for nutritional status evaluation of fruit trees [6,7,8], are sampled following this seasonal pattern. Nitrogen use efficiency (NUE) is of significant concern in horticulture. Nitrogen pollution of drinking water resources, originating from agricultural systems, is a major problem due to health risks [9,10]. Leaching from agriculture in general, and orchards has been reported to be a significant contributor to a growing global phenomenon of contamination of groundwater with nitrogen [11,12,13]
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