Precision Agriculture, 2, 319–332, 2000
© 2001 Kluwer Academic Publishers. Manufactured in The Netherlands.
A Methodology for Precision Nitrogen Fertilization
in High-Input Farming Systems
B. J. VAN ALPHEN AND J. J. STOORVOGEL
Laboratory of Soil Science and Geology, Wageningen University, P.O. Box 37,
6700 AA Wageningen, The Netherlands
Abstract. Nitrogen (N) emissions to ground and surface waters have become a major concern in many regions.
In reaction, policy makers are tightening environmental constraints on agriculture, resulting in a call for more
efficient management systems. This study presents a methodology for precision N fertilization in high-input
farming systems applying split fertilizer strategies. Essentially, the method uses a mechanistic simulation model
to quantify (i) soil mineral-N levels and (ii) N uptake rates on a real-time basis. Early warning signals are gen-
erated once N concentrations drop below a critical threshold level, indicating that additional fertilizer should
be applied. Thresholds are not static, but defined in relation to actual uptake rates. Spatial variation is incorpo-
rated through the concept of management units: i.e., stable units with relatively homogeneous characteristics
in terms of water regimes and nutrient dynamics. Separate simulations are conducted for each management
unit, based on selected representative soil profiles. The proposed methodology was tested in a winter wheat
(Triticum aestivum L.) field during the 1998 growing season. Six experimental strips were delineated receiving
either ‘precise’ or traditional fertilization. Precision fertilization proved efficient in reducing fertilizer inputs
−23%, while slightly improving grain yields +3% and hectoliter weights +4%. Results clearly illustrate
the significance of precision management in the process of increasing fertilizer use efficiency.
Keywords: precision agriculture, nitrogen fertilization, real-time modeling, management units
Introduction
From 1950 onwards the rapid intensification of agricultural production systems has
resulted in a dramatic increase of fertilizer inputs. Apart from boosting crop produc-
tion to high levels, agricultural emissions to the environment have steadily increased.
Nowadays, nitrogen (N) emissions to groundwater and surface waters have become a
major concern in many regions. Given the fact that agriculture is the main source of
these emissions, the European Community (EC) launched several directives to “reduce
water pollution caused or induced by nitrates from agricultural sources” (EC-Council
Directive, 1991). Stimulated by these directives, individual countries are in the process of
implementing a series of policies to tighten environmental constraints. In the Netherlands
this has resulted in an N-accounting system, referred to as ‘MINAS’. The system will
be used to charge levies on budgetary N surpluses at the farm level and is scheduled for
gradual implementation over the period 1998–2002. The final objective is to meet the
1980 EC-Drinking Water Directive in both groundwater and surface waters by limiting
nitrate concentrations to 50 mg NO
−
3
per liter (∼113mgNl
−1
).
Given the complexity of N dynamics in soils, it remains questionable whether a
relatively simple accounting system will suffice to control N losses. Several impor-
tant processes, such as the net-mineralization of N from soil organic matter (SOM),
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