Illinois
Fertilizer Conference Proceedings
January 27-29, 1997
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R.G. Hoeft, E.D. Nafziger, R.L. Mulvaney, L.C. Gonzini, J.J.
Warren, KB. Ritchie, and W.B. Stevens1
Nitrate contamination of surface water supplies has become a major concern for several Illinois cities. If the problem persists, some of these cities may be required to install treatment facilities at a cost of several million dollars plus hundreds of thousands of dollars for the annual operation of the equipment. Since agriculture is a large and visible user of nitrogen fertilizers, many in the non-agricultural community perceive the problem is entirely associated with farming; whereas many of the individuals actively engaged in farming perceive the problem as having multiple sources (Smicklas, 1995). Irrespective of whose perception is correct, those working in agriculture must attempt to ascertain techniques that will allow optimum crop production while maintaining N03-N levels in surface water supplies below the accepted standard.
A recent study by Keeney and DeLuca (1993), demonstrated that N03-N concentrations in the Des Moines River were similar in the 1980-1990 time period to those observed during 1945, even though fertilizer consumption had increased from 440 to 240,000 tons of N per year in the watershed. They concluded that intensive agricultural practices in both 1945 and in the late 1980's was the major source of nitrates to the river, rather than N fertilizer. They suggested that changes in cropping patterns and land use, along with use of buffer strips at field margins, restoration of wetlands and prairies in sensitive areas, fine tuning of fertilization practices, and improved livestock manure management would be required to markedly lower the nitrate levels of surface water in the river basin.
Some of our recent work would imply that some Illinois producers may be unknowingly contributing nitrates to water supplies (Brown, 1993). On-farm research identified 13 of 77 fields in which corn was non-responsive to fertilizer N. Phosphorus levels at each of these 13 non-responding sites were exceptionally high, indicating a past history of high levels of fertilization and/or manure application. Based on these results, along with some of our previous work (Torbert et al., 1992) showing that excess fertilizer N is assimilated into organic N compounds, we have theorized that these non-responding sites may have an accumulation of organic N compounds that may mineralize more easily than native organic matter, and thus decrease the need for fertilizer N in the short run. If that theory is correct, a reduction in N rates will be effective until the easily oxidizable N has been consumed, after which the need for supplemental N will increase. Continued application of optimum or above optimum N rates on these fields will enhance the potential for nitrate movement through tile line drainage.
The objectives of this project are to ascertain the effect of rate and time of N application on nitrate-N concentrations in water from tile lines and to evaluate the effect of site-specific N management on efficiency of N use.
Twelve fields that have clearly defined tile systems that drain only that field or a known portion thereof are being identified (five of the fields have been identified). Six of the fields will have a history of spring-applied N, with three of them having used rates equal to or below recommended levels and the other three having used rates at least 15 percent above recommended levels. The other 6 fields involved in the study will consist of 3 that have a history of fall or early spring N application and 3 that have utilized sidedress application. These latter six fields will have a history of using recommended rates of application. At all 12 fields, farmers will be asked to continue their past fertilization practices. Monitoring systems will be established to monitor the quantity and nitrate concentration of water flowing from the tile lines. In addition, soil and air temperature, daily precipitation (both intensity and total amount), soil moisture content at four depths, wind speed and direction, humidity, and solar radiation will be recorded. The climatic data will be used in an attempt to correlate net nitrogen mineralization rates to some or all of the climatic factors.
A nitrogen rate study will be established within each field to ascertain the optimum nitrogen rate for each site. Seven nitrogen rates ranging from 0 to 240 lb N/acre will be applied in 40-lb increments as ammonium sulfate. An eighth treatment consisting of 401b N/acre as diammonium phosphate applied in the fall plus 80 lb N/acre as ammonium sulfate applied when the rest of the N is applied will be included. At two locations, the diammonium phosphate will contain 15N. A microplot within each main plot will receive 15N-enriched ammonium sulfate at the same rates as the rest of the plots at four of the 12 locations. Soil samples will be collected in mid-summer and at physiological maturity of the crop to a four-foot depth in 6-inch increments for the first foot and then in 1-foot increments from each of these microplots and analyzed for total and inorganic nitrogen content. Total aboveground plant tissue will be collected at physiological maturity to determine the efficiency of fertilizer nitrogen uptake. The microplots will be relocated within each plot each year to allow for determination of the efficiency of fertilizer recovery over an extended time period.
In 1996, nitrogen rate experiments were conducted at 4 locations within the
Lake Decatur watershed. Nitrogen rates used in the experiments varied due to
the fact that three of the fields had received a fall application of diammonium
phosphate (DAP). At location 15 SD 1 where no DAP had been applied, nitrogen
was applied as ammonium nitrate at rates ranging from 0 to 240 lb N/acre in
increments of 601b N/acre. At this location, 15N was applied to microplots
at the 60, 120, and 180 lb N/acre rates. At the two locations where 36 lb N/acre
had been applied as DAP, the rates ranged from 36 to 2361b N/acre in 40-lb increments.
At the fourth location where 761b N/acre had been applied as DAP and ammonium
sulfate, the rates ranged from 76 to 2761b N/acre in 40-lb increments. All nitrogen
treatments were injected at sidedressing time as urea-ammonium nitrate solution.
During the growing season, SPAD meter readings were collected from each plot
every two weeks, starting in early July and continuing through late August at
15 SDI and OOSD2. Soil temperature data were collected from early. June through
mid-September, and soil and whole plant samples were collected at physiological
maturity to ascertain the fate of fertilizer N at these two locations.
The experimental areas selected have a long term record of high productivity (Table 1). While soil test data were not available at the time of publication, previous fertilization records would indicate that the fields have been well managed for several years. None of the locations had received manure within the last 4 years, but location OOSD2 is located near a livestock facility and has likely had some manure history. Soil temperature averaged approximately 78 degrees from early June through early September, reaching a peak of 90-95 degrees at the 4-inch depth in early June before the canopy had covered and then decreased as the season progressed (Fig. 1 and 2).
Increasing N rates resulted in increased corn yield at all locations (Fig.
3, 4, 5
and 6), although the optimum N rate necessary
to produce economically optimum yield were lower than would have been recommended
(Table 2). Optimum N rates were calculated
using a corn price of $2.75 per bushel with an N price of $0.22 per pound. The
reason for this lower than normal N requirement is not known, however, the excellent
yield levels attained not only at these sites, but for much of the state indicate
an excellent growing season, i.e. good moisture and temperature. Such conditions
likely resulted in a greater rate of release of soil nitrogen. Total nitrogen
uptake along with the "N results should enable us to determine the reason
for this atypical response.
SPAD meter readings collected at sites 15 SD 1 and 00SD2 were highly correlated
with yield response when averaged across all plots (Table
3). However, the relationship between SPAD readings for individual plots
and individual plot yield was much lower (Fig.
7 and 8). These results would imply
that in order to be useful, one would need to take multiple readings across
a field. At both locations, SPAD readings of 54-55 in early and late July were
associated with optimum yield in the fall. However, the SPAR meter readings
collected in mid-July had little relationship to optimum yield in the fall.
Climatic data indicate that the period prior to the mid-July data collection
had been relatively dry in contrast to the periods prior to the early and late
July samplings. This may imply that SPAD readings are less useful as a diagnostic
tool when plants are under environmental stress.
Table 1: Characteristics of experimental locations
Table 2: Optimum yield and optimum N rate
Table 3: Relationship between SPAD meter readings and corn grain yield
Figure 1. Soil temperature at 4" depth. Site 15SD1
Figure 2. Soil temperature at 4" depth. Site 00SD2
Figure 3. Effect of N rate on corn grain yield. Site 15SD1
Figure 4. Effect of N rate on corn grain yield. Site 00SD2
Figure 5. Effect of N rate on corn grain yield. Site 00SD3
Figure 6. Effect of N rate on corn grain yield. Site 00SD4
Figure 7. Relationship between SPAD meter readings and corn grain yield. Site 15SD1
Figure 8. Relationship between SPAD meter readings and corn grain yield. Site 00SD2
1 R.G. Hoeft and E.D. Nafziger are Professors, Dept. of Crop Sciences;
R.L. Mulvaney is Professor, Dept. of Natural Resources and Environmental Sciences;
L.C. Gonzini and J.J. Warren are Senior Res. Specialists, Dept. of Crop Sciences;
and K.B. Ritchie and W.B. Stevens are Jonathan Baldwin Turner Fellows, Dept.
of Crop Sciences, Univ. of Illinois
Brown, H.B., R.G. Hoeft, and E.D. Nafziger. 1993. Evaluation of three N recommendation
81 systems for corn yield and residual soil nitrate. Proc. IL. Fert. Conf 43-50.
Keeney, D.R. and T.H. DeLuca. 1993. Des Moines River nitrate in relation to
watershed agricultural practices: 1945 versus 1980's. J. Environ. Qual. 22:267-272.
Smiciklas, K.D. 1995. Personal communications.
Torbert, H.A., R.G. Hoeft, R.M. VandenHeuvel, and R.L. Mulvaney. 1992. Effect
of moisture regime on recovery and utilization of fertilizer N applied to corn.
Commun. Soil Sci. Plant Anal. 23:1409-1426.
