Illinois Fertilizer
Conference Proceedings
January 29-31, 1996
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Emerson D. Nafziger and Robert G. Hoeft
The ability of crop producers to make precise applications of fertilizers, seeds, and other inputs has increased rapidly in recent years with the development and commercialization of global positioning system (GPS) technology and with improvements in the precision and computerization of application technology. The availability of combine-mounted yield monitors has also allowed farmers to rather precisely test the effects of varying application rates on grain yield. The results of such research can be applied by varying application rates in different parts of the field in order to make most efficient use of inputs.
While there are a number of reports in the literature that deal with using variable rate technology (VRT) in order to more closely meet the crop nutrient requirements in different parts of variable fields (Wollenhaupt et al., 1994), there have been few published reports of research dealing with variable N rate effects in corn fields. Malzer et al. (1994) divided a field into six blocks, with five rates of N plus a variable rate in each block, and with plots running the length of the field. Silage yield data were taken each 50 feet along the length of each plot. Field maps were constructed showing spatial variations in silage yields and in the response to N rate.
This research was initiated in 1995 to test the feasibility of optimizing N
rates within parts of variable fields. We also hope to improve the ability of
participating farmers to carry out this type of research.
Eight Illinois farmer-cooperators agreed to participate in this study. All had combine yield monitors and access to equipment that allowed N rates to be changed quickly and accurately. Soils types were silt loam or silty clay loam, and productivity of all soils was high. The following table lists the names and locations of cooperators in the 1995 study, along with some information about the trial:
| Cooperator | County | Notes |
|---|---|---|
| Adams, John | Logan/McLean | Planted early June |
| Dalenberg, Ken | Champaign/Piatt | Stand affected by water |
| Harford, Doug | Grundy | No outstanding problems |
| Hunt, Andy | Grundy | Planted late May |
| Johnson, Mick | Morgan | No outstanding problems |
| Sauder, Ken | Tazewell | Planted early June |
| Reifsteck, John | Champaign | Slight stand problem: wet, then dry |
| Western, Kent | Morgan | Serious stand problem due to wet after planting |
A nitrogen rate trial with two or three replicates and six N rates was conducted in each field. A randomized complete block design will be used, with N rates of 30, 60, 90, 120, 150, and 180 lb N per acre. Strips ran the length of the field, with N rates applied as sidedress applications in all cases. The N source was anhydrous ammonia at six of the locations, and 28% liquid N at the two Morgan County sites.
Yields within each N rate were taken by the participating farmer using their
combine yield monitor. Data were collected on 3-second intervals, and individual
strips were identified as separate loads by the cooperators for ease of identification.
Using PC ArcInfo software, average yields were calculated for each 100 feet
down the field-length strips. This allowed us to examine N responses across
the six N rates within each replication, and within 100-foot segments of each
strip.
Of the eight trials in this study in 1995, five were planted in April or early May, and three could not be planted until late May or early June due to wet weather. The wet weather also caused some stand problems in several of the early-planted trials. All N applications went on as planned, however, and usable data were collected from seven of the trials.
Responses to N rate in different parts of the field are shown in Figure 1 for the Dalenberg field. Where data points are missing, all or some of the data in that segment of strip was absent or very low due to stand problems. The overall N response from this trial is shown in Figure 2. While the problem of uneven plant stands caused obvious difficulties in the ability to ascertain N responses within small parts of the field, the overall N response (Fig. 2) appears to have been measured reasonably well.
While not reported here, N responses at other locations ranged from moderate
to no response (at the Sauder field). With only one (rather unusual) year of
data, we are yet not able to draw strong conclusions about the usefulness of
looking at N responses in different parts of fields. The study will be continued,
with the only change being to ask cooperators to gather data on 1-second, rather
than 3-second, intervals.
Figure 1. N response of corn in different parts of the Dalenberg field, 1995
Figure 2. N response as assessed by the entire trial, Dalenberg location, 1995
Malzer, G.L., T.J. Graff, P.C. Robert, D.R. Huggins, D.J. Fuchs, W.H. Thompson, G.L. Gaalaas, and T.W. Bruulsema. 1994. Site specific crop management: N-response by soil condition at Hildreth site 1993. Field Research in Soil Science 1994, Miscellaneous Publication 83-1994, Minnesota Agricultural Experiment Station, University of Minnesota, St. Paul.
Wollenhaupt, N.C., R.P. Wolkowski, and M.K. Clayton. 1994. Mapping soil test phosphorus and potassium for variable-rate fertilizer application. J. Prod. Agric. 7:441-448.
