Agriculture Reference
In-Depth Information
of genotypes was obtained with the application of 122-215 kg N ha
−1
depending on the genotypes.
Half of this N should be applied at sowing in the furrow and the remaining half as top-dressing at
the active tillering growth stage. Fageria and Baligar (2001b) reported that in a field experiment for
3 years, maximum grain yield was obtained with the application of 209 kg N ha
−1
in the first year,
163 kg N ha
−1
in the second year, and 149 kg N ha
−1
in the third year. The average across 3 years'
maximum grain yield (6465 kg ha
−1
) was achieved with the application of 171 kg N ha
−1
in this
experiment (Fageria and Baligar, 2001b). Singh et al. (1998) reported that the maximum average
grain yield of 7700 kg ha
−1
of 20 lowland rice genotypes was obtained at 150-200 kg N ha
−1
.
8.3.4 a
doptInG
a
pproprIate
t
ImInG
of
a
pplICatIon
The timing of N application during crop growth is an important strategy in improving N use effi-
ciency. The N application according to plant needs may improve its efficiency and avoid its loss
from the soil-plant system. In other words, synchronizing of N application with N demand of plants
is an important strategy in improving N use efficiency. Application timing is one of the factors that
can influence the efficiency with which applied N is utilized by crops, and research on the optimum
application timing of fertilizer N has been extensive (Randall et al., 2003; Randall and Vetsch,
2005; Fageria, 2009, 2013, 2014). It has been reported by Matson et al. (1997) and Tilman et al.
(2002) that nutrient use efficiency is increased by appropriately applying fertilizers and by better
matching the temporal and spatial nutrient supply with plant uptake. Applying fertilizers during
periods of highest crop uptake, at or near the point of uptake (roots and leaves), as well as in smaller
and more frequent applications has the potential to reduce losses while maintaining or improving
the crop yield quantity and quality (Matson et al., 1996; 1997; Cassman et al., 2002). Rose and
Bowden (2013) reported that split application of the N fertilizer after crop emergence improves N
use efficiency, because plant roots had a chance to penetrate to depth and crop sink sizes are suf-
ficient to take up significant quantities of the soil-mobile nitrate.
N is lost from the soil-plant system via volatilization, leaching, denitrification, or runoff (Fageria
and Baligar, 2005; Fageria et al., 2006). This suggests that there is more N available for loss at any
time during the crop growing season if N is applied only once during crop growth. Hence, split-
ting N fertilizer applications during crop growth can reduce nitrate leaching and improve N use
efficiency. For lowland rice under Brazilian conditions, applying half of the N in a band at sowing
and the remaining 6-7 weeks later should increase both N fertilizer use efficiency and N uptake by
minimizing leaching opportunity time and better timing the N application to N uptake (Fageria and
Baligar, 1999). Fageria and Baligar (1999) reported that the agronomic efficiency of N in lowland rice
was higher when N was applied in a three-split application (one-third at sowing + one-third at active
tillering + one-third at panicle initiation) compared with the entire N applied at sowing. Split applica-
tion of N in sandy soils and high rainfall areas is most desirable. A study conducted by Fageria and
Prabhu (2004) in the Brazilian Inceptisol showed that N fractionated into two or three equal doses
produced a higher grain yield of lowland rice compared with the total applied at sowing (Figure 8.19).
Split applications of the N fertilizer are often recommended as a way to reduce N losses and
improve NUE. Sainz et al. (2004) conducted a field experiment on corn to evaluate the effect of urea
rate (0, 70, 140, and 210 kg N ha
−1
) at planting or the six-leaf stage (V6) and reported increased grain
yield (10.5 vs. 11.2 Mg ha
−1
) and N uptake (168 vs. 192 kg ha
−1
) when the N fertilizer was applied at
the V6 stage. In another experiment, N recovery by a corn crop was 58% for application at planting
and increased to 71% when N was applied at the V6 stage (Sainz et al., 1997). Same authors also
reported that the N losses were 5.5% when N was applied at sowing and reduced to 1% when it was
applied at the V6 stage.
The author also studied in another field experiment the influence of different rates and timing of
N application on lowland rice yield for three consecutive years (Table 8.8). Overall, the grain yield
was higher at 200 kg N ha
−1
compared to 150 kg N ha
−1
under all timing treatments. The maximum
grain yield at 200 kg N ha
−1
(one-third at sowing + one-third at 45 days after sowing + one-third
