Agriculture Reference
In-Depth Information
Chapter 10
Temporally and Spatially Dependent
Nitrogen Management for
Diverse Environments
William R. Raun, Ivan Ortiz-Monasterio, and John B. Solie
SUMMARY
(2) Preplant soil testing that can determine the
soil-available ammonium and nitrate forms
of nitrogen is valuable, but nitrogen
response varies considerably from year to
year and from fi eld to fi eld.
(3) Nitrogen-rich strips applied preplant in
wheat production fi elds can assist farmers
in determining accurate midseason fertil-
izer N rates.
(1) As annual world fertilizer nitrogen (N)
consumption approaches 100 million
tonnes, agriculture in particular must
manage fertilizer N more effi ciently for
grain production and to minimize adverse
environmental impact. Current practices
where almost all nitrogen is applied pre-
plant for wheat production are not envi-
ronmentally sensitive nor do they optimize
fertilizer use. Methods to increase nitro-
gen-use effi ciency are sorely needed.
(4)
A variant of this methodology, ramp cali-
bration strips, offers midseason visual
interpretation of N demand and an applied
method for optimizing fertilizer N.
INTRODUCTION
L.) farmers worldwide. In addition, extensive
research has shown that indigenous soil N
across the landscape can vary several-fold,
resulting in very different N recommendations
depending on the location within the fi eld. In this
chapter, we describe two alternatives which
improve upon current methods for determining
fertilizer N rates and have the fl exibility to be
used in environments ranging from 260-ha fi elds
in the High Plains of the US to 1-ha fi elds in
Sub-Saharan Africa (SSA).
A direct measure of N requirement can be
made with the ramp calibration strip (RCS),
which is superimposed on farmer practices at or
near planting. A range of N rates (zero to more
than suffi cient) is applied mechanically or by
hand. The RCS is urgently needed in wheat pro-
duction because N response varies considerably
Nitrogen (N) fertilizer is the most expensive input
for cereal production worldwide. What is proba-
bly most important about nitrogen requirements
in cereal crop production is that the demand
changes drastically from fi eld to fi eld and from
one year to the next. Of all the information that
should be communicated to farmers in any locale
is that this temporal and spatial dependency
infl uences optimum nitrogen fertilizer rates.
Long-term winter wheat (
T. aestivum
L.) research
in the southern Great Plains of the US has shown
that the average fertilizer-N application rates
would have been correct in the ensuing year only
20% of the time; yet, using the same rate from
one year to the next is common practice for wheat,
maize (
Zea mays
L.), and rice (
Oryza sativa
