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NITROGEN
FERTILIZATION FOR CORN PRODUCTION
WHEN USING
LEPA CENTER PIVOT SPRINKLERS
F.R.
Lamm and A. J. Schlegel1
ABSTRACT
A
four year study was conducted with LEPA (Low Energy Precision Application)
sprinkler-irrigated field corn in western Kansas on a deep, well-drained,
loessial silt loam to compare nitrogen (N) fertilization using preplant
broadcast or in-season LEPA fertigation for five different applied-N amounts
(0, 90, 145, 200 or 260 kg/ha).
Residual
soil N levels in the soil profile, corn yields, apparent nitrogen uptake (ANU),
water use, and water use efficiency (WUE) were utilized as criteria for
evaluating treatment differences. In general, results were similar for both
application methods, indicating that either method is acceptable for corn
production. Corn yield, ANU, and WUE
all plateaued at approximately the same level of total applied N, 180
kg/ha (145 kg/ha with either primary
method plus a 35 kg/ha starter application).
Average yields at this level was 13.8 Mg/ha. Soil nitrate concentrations to a depth of 2.4 m for this same
treatment were below 5 mg/kg at the conclusion of the study. The results emphasize that high-yielding
corn production also can be efficient in nutrient and water use.
KEYWORDS. Sprinkler irrigation, nutrient management, nitrogen application,
water use efficiency
INTRODUCTION
Low energy precision application (LEPA)
sprinkler irrigation is a fast-growing irrigation technology in the U.S. Great
Plains. This system applies water as a line source (1.5 m spacing applied
between two 0.76 m corn rows) at a height of approximately 0.45-0.6 m above the
soil surface. This can be very
advantageous from a water conservation standpoint, reducing both evaporation
due to wind and also reduced evaporation from wetting less of the soil
surface. However, it has the potential
to be an advantage or disadvantage when used in combination with fertigation
(fertilizer applied with the irrigation water). Using proper management it could result in reduction of
fertilizer use similar to reductions applied to traditional banding of
fertilizers. Used with inappropriate
management, it could increase the chances for groundwater contamination,
because as fertilizer would be applied in a smaller zone and then "pushed
downward" by the "slug" of irrigation water. Irrigators are already investing heavily in
LEPA sprinklers. Fertigation in
combination with LEPA also is likely to be a widely utilized technology, but
some producers will continue to apply N fertilizer through traditional methods. This study compared N fertigation with LEPA
sprinklers to a more conventional preplant-broadcast application method.
1 The authors are Freddie R. Lamm, Research
Irrigation Engineer, Northwest Research-Extension Center, Kansas State
University, Colby, KS., Email:
flamm@ksu.edu, Phone: 785-462-6281,
Fax: 785-462-2315 and Alan J. Schlegel,
Research Soil Scientist, Southwest Research-Extension Center, Kansas
State University, Tribune, KS.
This is contribution no. 00-271-A from the Kansas
Agricultural Experiment Station. Any
opinions, findings, conclusions, or recommendations expressed in this
publication are those of the authors and do not necessarily reflect the views
of Kansas State University or the US Department of Agriculture. This research was partially funded by the
Kansas Corn Commission.
PROCEDURES
The
project was conducted with field corn from 1993-1996 at the KSU Northwest
Research-Extension Center at Colby, Kansas on a deep, well-drained,
medium-textured loessial silt loam. The continental climate was semi-arid with
an average annual precipitation of 474 mm and annual lake evaporation of 1400
mm. Irrigation was scheduled using a
climatic water budget.
The
study area accommodated 30 plots in a randomized complete block design of 2
whole-plot treatments (preplant
broadcast or LEPA fertigation) and 5 sub-plot treatments (0, 90, 145, 200 or
260 kg/ha of N) with 3 replications. The experimental treatments were applied
during the 1993 corn-growing season to develop approximately equilibrium
nitrogen levels in the soil profile and crop residue before the 1994
season. No further discussion of the
1993 season will be made. Each plot was
approximately 12 m wide and 20 m long with circular row direction running
parallel to direction of center pivot sprinkler travel. Each LEPA sprinkler
effectively irrigated 2 corn rows. All
N in the study was applied as an experimental variable except for the small
amounts supplied by the spring starter fertilizer application (approximately 35
kg/ha of N and phosphorus (P) each).
The N source, urea-ammonium-nitrate (UAN, 32-0-0) was either preplant
broadcast in one application prior to corn planting or injected in weekly
increments into the center pivot lateral for LEPA fertigation. Weekly
fractional amounts to be applied were estimated from a N-use curve developed at
Iowa State University (Ritchie, et al., 1989).
Fertigation was begun about mid-June with the final fractional amount of
N (usually around 20%) applied in mid-August.
Water
use was calculated as the sum of seasonal changes in soil water between the
first and last sampling dates, irrigation, and rainfall. Furrow dams restricted runoff. Available soil N (ammonium and nitrate N) was determined for each plot at the
initiation and conclusion of each cropping season to a depth of 2.4 m. The apparent nitrogen uptake (ANU) was
calculated from the field biomass levels and the whole-plant N content at
physiological maturity. Grain yield was
determined from a hand-harvested sample at physiological maturity. Water use
efficiency (WUE) was obtained by dividing crop yield by water use.
RESULTS AND DISCUSSION
Climatic Conditions
Precipitation during the crop period was 277, 280
and 518 mm in the respective years 1994, 1996 and 1996 compared to the 25-year
mean of 315 mm. The cumulative calculated ET was slightly above the 25-year
mean of 577 mm in 1994 (628 mm) and 1995 (590 mm) but significantly below the
mean in 1996 (494 mm). In this study,
seasonal irrigation amounts were 373, 394 and 152 mm in 1994-96, respectively,
compared to a long-term normal net irrigation requirement of 391 mm. Although the climatic conditions for the
three years varied, they did represent a good range of conditions.
Residual Nitrate-N in the Soil Profile
After four years (1993-1996, with 1993 not included in analysis) of continuous application of the fertilizer treatments, nitrate-N levels in the soil increased with increasing rates of applied N under both preplant broadcast application and LEPA fertigation (Figure 1). In general, the nitrate concentrations were less than 10 mg/kg. An exception for the preplant broadcast application was a 17 mg/kg concentration near the soil surface for the 260 kg/ha applied N rate. Elevated soil nitrate concentrations (15 mg/kg) also occurred for the 200 and 260 kg/ha LEPA fertigation treatments at the 0.6 to 0.9 m depth. This actually may indicate fewer volatilization losses with this application method which resulted in more N available to move to the deeper depth. The nitrate concentration at the end of the study did not exceed 5 mg/kg for N rates 145 kg/ha or less for either application method. In terms of nitrate concentrations, a best management practice (BMP) would be to apply not more than 180 kg/ha of N (145 kg/ha preplant broadcast or LEPA fertigation and additional 35 kg/ha of N as part of a starter fertilizer program). The soil profiles for the 260 kg/ha N rate for the six different sampling periods indicates that leaching did not occur in every year even for the higher N rate (Figure 2). If N runoff is a concern, these data indicate that LEPA fertigation with incremental applications can reduce the pool of N available for runoff.
Figure 1. Soil nitrate-N concentrations as a function
of depth for the five applied-N rates for preplant broadcast and LEPA
fertigation application methods. Total applied N exceeded fertilization level
shown in graph by N starter application of 35 kg/ha.
Corn Yields
No significant differences (P=0.05 significance level) in corn yields occurred in any year as affected by application method (Table 1). However, corn yields were significantly (P=0.05 significance level) different among N rates in all three years but generally were similar at and above the 145 kg/ha applied N rate (Table 1 and Figure 3). Overall yields were high (13-14 Mg/ha) even when including 1995 yields that were lowered by hail and poor growing conditions. This data would continue to support the BMP of 180 kg/ha (primary plus starter application) of N to optimize corn yields.
Figure 2. Soil nitrate-N concentrations as a function
of depth for six sampling dates for the 260 kg/ha N rate applied preplant
broadcast or with LEPA fertigation. Total applied N exceeded fertilization
level shown in graph by N starter application of 35 kg/ha.
Apparent Nitrogen Uptake
The
amount of N in the aboveground biomass was significantly different (P=0.05)
between application methods in only one year, being higher for the LEPA
fertigation method in 1994 (Table 1).
Applied-N rate affected ANU in all three years with higher applied-N
increasing ANU. The three year average
ANU exceeded the total amount of applied N for both application methods up to
235 kg/ha N rate (200 + 35 kg/ha
primary and starter application), indicating good use of the applied N (Figure
3).
Water Use and Water Use
Efficiency
Water use was affected by application method only in 1995 with LEPA fertigation requiring less water (Table 1). Water use differed significantly (P=0.05) among N rates only in 1996 but tended to be higher for applied-N rates greater than 0 kg/ha in all three years. Irrigation amounts were identical among treatments so it can be concluded that adequate levels of fertilization can help better utilize available soil water. WUE was not affected by application method in any year. WUE was significantly different (P=0.05) among N rates (Table 1) with a trend toward WUE maximization at a total applied-N rate of 180 kg/ha (Figure 3). The plateauing of WUE coincided with plateauing of corn yield and ANU at approximately 180 kg/ha of total applied-N.
CONCLUSIONS
In
general, no appreciable differences occurred between preplant broadcast and
LEPA N fertigation methods for corn production in terms of grain yields,
nutrient uptake, residual soil N, water use or water use efficiency.
Increasing
the applied-N rate to 200 kg/ha with an additional 35 kg/ha of starter N tended
to increase nitrate concentrations in the soil profile above 5 mg/kg. The lower 145 kg/ha N application rate was
not appreciably different from the control treatment with no primary N
application. A primary application of 145 kg/ha of N using either application
method with the addition of a 35 kg/ha N starter application optimized grain
yields at approximately 13.8 Mg/ha. Similarly, apparent nitrogen uptake and
water use efficiency tended to plateau at the 145 kg/ha N level. This
emphasizes that high-yielding corn production also can be efficient in nutrient
and water use.
REFERENCES
Ritchie,
S. W., J. J. Hanway, and G. O. Benson.
1989. How a corn plant
develops? Iowa State University,
Cooperative Extension Service, Ames, Iowa.
Special Report No. 48. 21 pp.