Agriculture Reference
In-Depth Information
0
100
400
600 mg N kg
-1
200
FIGURE 3.24
(
See color insert.
) Response of dry bean to nitrogen fertilization to a Brazilian Oxisol. Half
of the N was applied at sowing and the remaining half as topdressing at 35 days after sowing.
recommended taking a minimum of one composite sample per 12-15 hectares for lime and fer-
tilizer recommendations. A representative soil sample is composed of 15-20 subsamples from a
uniform field with no major variations in the slope, drainage, or past fertilizer history. Any of these
listed factors, if changed, will have an effect on the number of samples and unit area from which
the sample is obtained.
Generally, soil samples are collected from a 0 to 20 cm soil depth for making fertilizer rec-
ommendations for field crops, because a major part of the roots of field crops is located in this
layer (Fageria, 2013). However, Fageria and Baligar (2005a) reported that the depth of sampling for
mobile nutrients such as nitrogen should be 60 cm, and for immobile nutrients such as P, K, Ca, and
Mg, a 15-20 cm sampling depth can give satisfactory results. For pasture crops, a sampling depth
600 mg N kg
-1
200
400
100
0
FIGURE 3.25
(
See color insert.
) Growth of wheat at different N levels. Half of the N was applied at sowing
and the remaining half as topdressing at 35 days after sowing.
