Nitrogen nutrition and metabolism in fruit trees

During 1992-1995 a study of nitrogen nutrition was carried out in commercial apple orchards located in the southern part of Finland, including the land Islands. In the experimental material we had 12 cultivars as follow Maikki, Transparente Blanche, Red Melba, Atlas, Red Atlas, Jaspi, Lobo, Ranger, Aroma, Akero, Same and Raike. The results of the study showed that nitrogen content ranged 14-28 and 1.6-7.1 g/kg of dry weight in leaves and fruit, respectively. In a part of leaf samples, nitrogen content was under the recommendation limits, 20-30 g/kg. The soil mineral nitrogen in the depth of 0-50 cm varied between 4.3 and 18.5 mg/l. Nitrogen in leaves and fruit did not correlate significantly with soil nitrogen. In soils with higher nitrogen level, nitrogen in fruit and leaves did not increase as compared with other samples. Also, the relationship between leaf and fruit nitrogen was not very clear. Nitrogen content should be between 500 and 600 mg/kg of fresh weight. If nitrogen content exceeds 600 mg/kg of fresh weight, fruit become less firm and become more prone to storage disorders.