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The timing of N application in dryland soils is very important. It is the most
beneficial when applied as basal dose; nonetheless split application from sowing to
early leaf boot stage in wheat can be useful when season is longer than normal
(Mason 1975 ), and more rainfall is expected. Based on several field experiments,
Spratt and Chowdhury ( 1978 ) reported that split application of N was beneficial for
sorghum, pearl millet, maize and upland rice under dryland conditions in India.
Fillery and McInnes ( 1992 ) reported less than 50 % recovery of applied N in dry-
land wheat.
Optimum N application to wheat crop in dryland soils depends upon the input of
N from soil organic matter, fixation by legumes, N losses through vitalization and
leaching, and the crop demand. Westfall et al. ( 1996 ) reported that the N fertiliza-
tion in dryland crop production must be managed carefully to gain high economic
returns. In dryland crop production systems, the rate of N application is more
important than its placement method. However, the placement becomes important
with the increase in rainfall incidence. The subsurface N placement is better than the
surface broadcast applications. In China, deep placement of N fertilizer is recom-
mended for dryland soils because of the availability of surplus water in deeper soil
layers. In deeper layers, more roots are present which may use the applied N very
efficiently and thus help improving the fertilizer use efficiency (Li et al. 2009a).
Other studies have also reported that deep placement of N fertilizer improves the N
use efficiency and crop yield (Li et al. 1976b). Rees et al. ( 1997 ) reported 18 % N
recovery from surface applied N, 33 % from the N mixed with 15 cm soil, and 36 %
when N was applied in a pit (15 cm deep). In another study, Lu and Li ( 1987 ) found
that deep placement of N and P fertilizer enhanced the fertilizer use efficiency and
wheat yield by 20 %, and reduced the losses of ammonium-N through volatilization
by 14–39 % for urea, and from 36 to 54 % for ammonium bicarbonate. Li ( 2007 )
reported a reduction in N loss through ammonia volatilization by 29 %, 15 % and
1 %, when the N fertilizer was surface applied, soil mixed, or was deeply placed,
respectively.
In dryland regions, the early application of organic and P fertilizers is as useful
as that of N (Li et al. 1976a). The usefulness of fertilizer application method may
vary with crop type. For instance, Kanwar and Rego ( 1983 ) reported that split band
application of urea in pearl millet and sorghum was better than broadcasted urea
(incorporated or either left on surface). However, in sorghum, split application of N
fertilizer (either broadcasted, band application) improved the grain yield than that of
other N application methods (Kanwar and Rego 1983 ). Drilling the N and P fertil-
izers in the moist zone (5–7 cm below seed) improved the sorghum grain yield by
60 % than its application by the furrow side (Randhawa and Singh 1983 ).
Due to high pH buffering capacity of dryland soils, nitrate-N is the main form of
N taken by plants in dryland soils. Major crops such as wheat and maize grown in
dryland regions also respond better to nitrate-N than ammonium-N. Thus, it is not
wise to use ammonium-based N fertilizer (e.g., urea) in dryland soils. However, if
no other source of N fertilizer is available, pretreating of the dryland soil with a
small quantity of NH 4 + salt before application of a large amount of urea is beneficial
to reduce the nitrification of ammonical N (Li et al. 2009a).
A. Nawaz and M. Farooq