Nitrogen Fractions in Arable Soils in Relation to Nitrogen Mineralization and Plant Uptake

Abstract

Nitrogen (N) as a major constituent of all plants is one of the most important nutrients. Minimizing input of mineral nitrogen fertilizer is needed to avoid harm to the environment. Optimal input of mineral nitrogen should take the nitrogen supply of the soil into account. Many different soil tests have been proposed for determining soil nitrogen availability. In this article we present a new approach that is based on the measurement of nitrate, ammonium, and dissolved organic nitrogen (DON) in a 0.01 M CaCl₂ soil extract. Eighteen agricultural soils, differing widely in the availability of nitrogen were used, fertilized and unfertilized. It is shown that the nitrogen uptake by maize plants (Zea Mays L.) in both “N‐fertilized” and “N‐unfertilized” soils as measured in a pot experiment can be described with a simple model using the measured nitrogen fractions in the extract. The main source of nitrogen uptake by the plants is the mineralized organic nitrogen during the growing period. It is shown that the initial measured DON fraction is a good indicator of the nitrogen mineralized during plant growth.

Keywords:

• Arable soil
• CaCl₂ extraction
• DON
• mineralization
• mineral nitrogen
• nitrogen fractions

Acknowledgments

Special appreciation is expressed to V. J. G. Houba and I. Novozamsky for their assistance in this study. We thank E. Hoffland for valuable comments on the manuscript. Thanks to the Department of Soil Quality from the Wageningen University for the use of the greenhouses and the Central Laboratory, where the analytical determinations were performed. This work was developed with the financial support of a grant awarded in the context of the Netherlands Fellowships Programme of the Government of The Netherlands, and partial support was obtained from the Science and Technology Secretary Austral Patagonia National University (SeCyT UNPA Argentina).