NITROGEN FERTILIZER REQUIREMENTS OF FRUIT TREES AS RELATED TO SOIL MINERAL NITROGEN CONTENT IN SPRING

Soil mineral nitrogen content (mainly nitrate) in the rooting zone at the beginning of a growing season has been shown to be a useful indicator of nitrogen fertilizer requirements for cereals, sugar beets and vegetable crops.
This procedure, called the ‘N_min-Methode’, has been used successfully in agriculture on loess soils in the southern part of Niedersachsen since 1977. This paper reports on the application of the same procedure to orchards.
First results allow the following statements:

1. Soil mineral nitrogen content differs among sites by several hundred kg ha^-1. Differences are clearly related to fertilizer applications in previous years.

2. Only small quantities of available nitrogen are found under the grass strip between tree rows.

3. In contrast to the sharp decrease during the growing season under wheat or sugar beets, soil mineral nitrogen remains almost constant in the herbicide-treated strip of orchards.
   This is attributed to the relatively small nitrogen requirement of tree and nitrogen release through mineralization.

4. There is a positive relationship between soil mineral nitrogen content in February and March and leaf nitrogen content in July and August.
   It is therefore possible to estimate the nitrogen supply of an orchard by soil analysis in springtime.

Symposium on Mineral Nutrition and Fruit Quality of Temperate Zone Fruit Trees

J. WEHRMANN, H.C. SCHARPF

https://doi.org/10.17660/ActaHortic.1980.92.58