Relationships between soil nitrogen availability indices, yield, and nitrogen accumulation of wheat
Walley, F., T. Yates, J.W. van Groenigen and C. van Kessel. 2002. Soil Sci. Soc. Am. J. 66: 1549-1561
Abstract
The success of variable rate N
fertilizer application rests on our ability to predict
the contribution of soil N to growing crops. We assessed
relationships between soil N availability indices
(SNAIs), yield, and total N accumulation of wheat (Triticum
aestivum L.) grown in a typical glacial till
landscape in Saskatchewan, Canada. Soil samples were
collected at 3-m intervals along a 300-m transect
comprised of low (LCFS) and high catchment footslopes
(HCFS), and low (LCSH) and high catchment shoulders
(HCSH). Total soil N and C, organic C, mineral N, depth
of A horizon, spring soil moisture, grain yield, and
total plant N were measured. Soil N availability indices
used in this study included: (i) cumulative N released
during a 2-wk aerobic incubation (NMIN); (ii)
potentially mineralizable N estimated using a 16-wk
aerobic incubation (N0); (iii) NO3
sorbed on anion-exchange membranes (NO3AEM);
(iv) N extracted with hot KCl (NKCl); and (v)
N hydrolyzed with hot KCl (NHYDR). Although
all SNAIs were significantly correlated to yield and,
with the exception of N0, total plant N when
analyzed across the transect, typically <40% of the
yield variability was explained. Forward stepwise
regression revealed that most SNAIs failed to explain
more variability in crop N accumulation than did basic
soil properties or relative elevation. Although these
results do not invalidate the use of SNAIs for soil
testing purposes, it is clear that SNAIs must be combined
with additional information about field scale variability
for predicting fertilizer N requirements. Without this
information, grid sampling as a means of assessing N
requirements remains ill-advised for glacial till
semi-arid landscapes.
