Agriculture Reference
In-Depth Information
applications should not exceed 11.2 kg ha
−1
of N and K combined (Laboski, 2008). It is not clear
if this information can be used for different soil types. This lack of consistency is probably due
to differences in soil texture and soil moisture. Rehm (1999) reported that 10-15-0 (N-P-K) can
be safely applied with the seed at rates up to 132 kg ha
−1
as long as the soil moisture is adequate.
Niehues et al. (2004) reported that applying 22 kg ha
−1
as NH
4
NO
3
(34-0-0, N-P-K) and K kg ha
−1
as KCl (0-0-50, N-P-K) did not have any effect on plants standing on a silt loam soil. Kaiser and
Rubin (2013b) reported that 10.6 kg N + K ha
−1
could be applied for clay loam and silt loam soils
while the rate was 5.7 kg for fine sand.
Soil moisture is important to take into account when applying fertilizer directly with the seed.
Raun et al. (1986) found significant stand loss as a result of the relatively dry soil conditions. Salt
damage from fertilizer is often more severe on dry soils because the ion concentration in the dry
solution becomes greater (Kaiser and Rubin, 2013b). A large ion concentration around the root will
move water out of the plant cells and induce injury (Laboski, 2008). Fertilizer sources that cause a
higher amount of damage to seedlings are those that release free NH
3
, including urea and diammo-
nium phosphate. These sources cause severe damage when placed in direct contact with germinat-
ing seeds (Kaiser and Rubin, 2013b).
Nitrogen fertilizers are broadcast and mixed into soil before crop sowing. They may also be
applied in rows below seeds at sowing and may be banded in rows beside seeds at planting or pre-
emergence. During postemergence, fertilizers may be side-dressed, injected into the subsurface,
and top-dressed. Fertilizers that are mixed into the soil or injected into the subsurface are more
efficient methods of N application compared to broadcast and left on the soil surface. The side-dress
application, N fertilization several weeks after corn emergence, has maximized the efficiency of fer-
tilizer N in most situations (Fageria and Baligar, 2005). Placement of urea or ammonium sulfate in
the anaerobic layer of flooded rice is an important strategy to avoid N losses by nitrate leaching and
denitrification (Fageria and Baligar, 2005). Savant et al. (1982) reported that lowland rice recovered
50-61% of applied N from deep placed urea supergranules when the average N recovery efficiency
of this crop is less than 40% (Fageria et al., 2003a,b).
The use of strip-till (ST) is another N management practice to improve its efficiency in crop
plants. ST is a minimal tillage practice that allows for deep, banded placement of dry, liquid,
or gas-based N fertilizers within tilled, planted rows without requiring tillage of the entire field
(Nash et al., 2013). Because only the crop rows are tilled, ST allows for many of the soil con-
servation and fertility benefits associated with NT practices to be maintained while lowering
the potential for significant N loss occurring with a fall fertilizer application through deep band
placement. An additional benefit of tilling the soil in the seeded row is that it breaks up soil
aggregates incorporating surface residues that lower bulk density, and increases internal drainage
and drying within the seedbed. These effects of tillage ultimately allow for earlier warming of
the soil in the spring, which has been reported to increase plant emergence and growth (Randall
and Vetsch, 2005). Although studies are limited, ST has been found to produce yields similar to
those of NT (Al-Kaisi and Licht, 2004; Vetsch and Randall, 2004; Al-Kaisi and Kwaw-Mensah,
2007; Nash et al., 2013).
8.3.3 u
se
of
a
dequate
r
ate
The use of an adequate rate is fundamental for meeting plant N demands, minimizing N losses, and
improving N use efficiency in crop production (Lopez-Bellido et al., 2006). The application of the
most optimal N fertilizer rate is a major factor in determining economic viability, crop productiv-
ity, and environmental quality. An adequate rate of mobile nutrients in a soil-plant system such as
N is determined by experimental data generated under field conditions. Before making N recom-
mendations for a given crop, it is essential that field experiments should be conducted under differ-
ent agroecological conditions for several years. This is essential to get average values of different
environmental conditions such as climate and soil types. An adequate time period to repeat field
