abstracts - INCDCSZ Brasov

POTATO CROP NITROGEN STATUS (CNS) ASSESSMENT TO IMPROVE N
FERTILISATION MANAGEMENT AND EFFICIENCY
Goffart J.P.
Walloon Agricultural Research Centre, Crop Production Department, rue du Bordia, 4
5030 Gembloux - Belgium – goffart@cra.wallonie.be
Introduction
The effects of excessive or insufficient nitrogen application of N fertilizer to potato crop are
well known on tuber yield and quality, but also on the N losses that can occur to the environment.
So there is a clear need to convince potato farmers to apply the right N fertiliser rate in the right time
and at the right place to maximise income, and to stay within the constraints of expected tuber quality
and respect of the EU nitrate directive (91/676/EEC). Recent increase in N fertilizers prices should
also significantly drive farmers to more careful input management.
With regard to apply the whole recommended amount of N fertilizer at planting, it is generally
agreed that the establishment of a field-specific N recommendation for potato at planting time can
never be accurate as it is not possible to predict with precision the total crop N requirements and soil
mineral N supply that will occur during the growing season. Such variables are influenced by several
predictable or unpredictable factors, such as weather conditions, chemical and physical soil properties,
type and evolution of organic matter previously incorporated in the soil, cultural practices, variety
earliness and crop duration.
N fertilization strategies that combine splitting of N fertilizer recommendation with the
assessment of crop N requirement during the growing season can largely help to better match needs
and supply, and as a consequence to improve N fertilizer efficiency (Vos and Mackerron, 2000).
The considerable advances that have been recorded the last decade in the understanding and modelling
of N cycle transformations in the soil-crop system and also in the modelling of potato N-uptake and
potato growth can be integrated in such strategies. At the same time, continuous improvements arise in
the technologies useful for in-season monitoring of CNS. Such tools are useful to fine-tune crop N
requirement and consequently can help to decide on the need for supplementary fertilizer N
application as top-dressing.
Combination of on the one hand modelling approach to establish a global N recommendation
at field-specific scale and on the other hand CNS monitoring tools can lead to the building of Decision
Support System useful to optimise N fertiliser rate.
The use of CNS assessment is based on the consideration that instead of attempting to finely
predict mineral N supply from the soil, it may be simpler to rely on the crop itself to indicate its N
status in order to respond accordingly. Crops are indeed often considered good integrators of growing
season conditions factors such as the presence of mineral N in soil, the weather and crop management
(Schroder et al, 2000).
This abstract paper deals with the state of the art and potential development on characteristics,
use and implementation of well-known and more recent methods aimed to assess in-season potato
CNS. The main objective remains to improve the management of N-fertiliser and its efficiency
through the integration of CNS assessment into DSS. Such an approach asks to deal N fertilisation
management towards areas with sub-optimal growing conditions for N availability, particularly by
avoiding excess N application at planting time (MacKerron, 2000).
Methods to assess potato CNS
What is CNS? The N status of a crop can be described as the comparison of the current
nitrogen content in the crop to the critical crop N content required to avoid crop N deficiency inducing
risk of yield losses. CNS can be assessed either through plant N concentration (expressed in percent of
N in the dry biomass) or crop N uptake (expressed in kg N per ha of soil area) determination.
On this base, methods aiming to monitor CNS have to lead directly or indirectly to a good
evaluation of whole crop N content. Ideal basic requirements for such methods are:
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