European Journal of Agronomy 13 2000 101 – 110
Nitrogen losses from entire plants of spring wheat Triticum aesti6um from tillering to maturation
Evan Rroc¸o, Konrad Mengel
Institute of Plant Nutrition, Justus-Liebig-Uni6ersity, Su¨danlage
6
,
35390
, Giessen, Germany Received 19 February 1999; received in revised form 26 July 1999; accepted 9 November 1999
Abstract
The release of nitrogen by roots of intact spring wheat plants into the soil and other losses, mainly of volatile N, have been investigated in two subsequent years from tillering until maturation, by use of a new technique for plant
labelling with
15
N. Plants were at first labelled by growing them in a
15
N nutrient solution until tillering and then after thoroughly washing the roots with distilled water, the entire plants were transplanted into pots filled with a silty loam.
15
N release was analysed throughout the growth of the plants at 6 days after transplantation tillering, ear emergence, beginning of grain filling, and full maturation. At these stages
15
N was analysed in the plant and in the soil. Release rates of labelled N into the soil were low in the period from tillering to ear emergence and increased progressively
attaining maximum rates in the phase from ear emergence to grain filling. The non-accounted for losses of labelled N, mainly volatile losses, were also found to be highest from ear emergence to the beginning of grain filling. © 2000
Elsevier Science B.V. All rights reserved.
Keywords
:
Nitrogen; N release by roots; Wheat; N loss www.elsevier.comlocateeja
1. Introduction
As yet little is known in quantitative terms of the loss of nitrogen from entire plants at various
stages throughout their growth. Different forms of N loss may be distinguished, such as N recy-
cled by plant roots into the soil, N released by upper plant parts into the atmosphere, mainly as
gases such as NH
3
and NO
x
Farquhar et al., 1983, and the loss of N by the removal of plant
parts as pollen, flowers, leaves and fruits Wetse- laar and Farquhar, 1980. Nitrogen loss may also
occur by leaching of N from upper plant parts, e.g. by rainfall. The quantitative evaluation of
these losses is of fundamental importance in es- tablishing reliable N balance sheets. Nitrogen re-
lease from plant roots into soil has been studied by various authors and losses have been found to
range from 6 to 33 of the total plant N Janzen, 1990; Lynch and Whipps, 1990; Janzen and Bru-
insma, 1993; Reining et al., 1995; Toussaint et al., 1995. This wide variation in results may partly be
accounted for by different experimental condi-
Corresponding author. Tel.: + 49-6403-62313; fax: + 49- 6403-62313.
E-mail address
:
konrad.mengelernaehrung.uni-giessen.de K. Mengel.
1161-030100 - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S1161-03010000068-X
tions but additionally it may originate from the different experimental techniques used.
In order to distinguish between the soil N and root borne N, plant N must be labelled and this is
generally done using
15
N. Reining et al. 1995 used the ‘split-root-technique’ in order to label the
plant N. This method allows the precise quantifi- cation of released N from the root part not in
contact with the labelled soil N. This procedure, however, does not allow the quantitative determi-
nation of labelled N released by the entire root system. Janzen and Bruinsma 1989 labelled their
plants by the uptake of
15
NH
3
by the upper plant parts. Unfortunately the amount of labelled N
taken up is small and therefore it is difficult to quantify the release of labelled N by the roots
over longer periods of time. Since the labelling methods used to date all have their shortcomings
Palta et al., 1991, we have developed a new technique for labelling entire plants with
15
N which is particularly suitable for measuring N
losses from tillering until maturation. The princi- ple of our method is the labelling of seedlings in
15
N nutrient solution prior to planting into pots filled with soil.
The objective of our investigation was to quan- tify the labelled N released from intact wheat
roots into the soil as well as other losses mainly into the atmosphere at distinct growth stages of
the plants: tillering, ear emergence, beginning of grain filling, and maturation.
2. Materials and method
