Urearuiskutusten vaikutus omenapuun lehtien typpipitoisuuteen

Abstract

In 1954 and 1955 experiments were made by spraying with 1.0 and 0.75 % urea solution the foliages of the Melba, Lobo, Antonovka and Åkerö apple varieties. In both year eight trees of each variety were included in the trials. All the trees grew in sod mulch in the same block. Urea was applicated four times after the flowering of the trees. In addition to urea sprays the trees received each year early in the spring 400 kg ammonium sulphate per hectare. The effect of the urea sprays were studied by analysing leaf samples taken three times during the the growing season. The growing seasons 1954 and 1955 differed remarkably of each others in regard of the monthly rainfalls (Table 1). In 1954 the rainfalls of May and June were small, but in July and August they exceeded markedly those of normals. In 1955 on the contrary the rainfall was in May rather high, but in June, July and August very scanty. Especially July and August were exceptionally dry. The results of the experiments are given in Table 2, also in Fig. 1. The nitrogen content of the leaves of the control trees followed the changes which occurred in rainfalls during the growing seasons. When the rainfall got down, the nitrogen of the leaves decreased. This is especially clearly to be seen in the results of 1955 (Fig. 1). The nitrogen content of the leaves of the control trees dropped then during July 0.3—0.8 %. Decreasing of nitrogen was greatest in the leaves of the Åkerö trees. The urea sprays had a very marked effect on the nitrogen content of the leaves. Owing to the sprays it increased considerably. In September, however, seven – eight weeks after the last urea spray, the nitrogen of the leaves reached about the same level as in the control trees. The differences of the nitrogen content of leaves between treated and control trees were very clear in the dry summer 1955. After the fourth application the leaves of treated trees contained 0.62—1.19 % more nitrogen than those of the control trees.