| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Dep. of Agron., 210 Waters Hall, Univ. of Missouri, Columbia, MO 65211
* Corresponding author (scharfp{at}missouri.edu)
Received for publication June 25, 2001.
 |
ABSTRACT |
|---|
 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
|---|
|
INTRODUCTION |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
|---|
Planting time is one of the busiest and most time-sensitive periods of the year for grain producers and is an inconvenient time to apply N fertilizer. Moving N applications away from this busy period is the main motivation for fall applications of N. Unfortunately, fall N application creates a substantial risk of losing N and yield (Blackmer, 1996). Nitrogen applications after planting offer an alternative way to move N applications away from the busy planting season but are seldom used by producers. There are many reasons for this, one of which is the fear that irreversible yield loss will occur due to N stress, especially if weather causes delays in the planned application timing.
Delaying application of some or all N fertilizer until after planting may allow for precise diagnosis of N needs, by either in-season soil testing (Blackmer et al., 1989), sensing crop color (Varvel et al., 1997; Blackmer et al., 1996), or estimating weather effects on soil N availability (Honeycutt, 1994). Application rates that precisely match crop needs could result in less residual soil NO-3 available for leaching (Andraski et al., 2000) and positively impact water quality. Understanding the effect of delayed N application on yield is critical to the use of any of these management tools.
Fertilizer N recovery by the crop may sometimes be greater when N application is delayed compared with application at planting (Russelle et al., 1983; Jokela and Randall, 1997). This is probably due to greater exposure of N applied at planting to a range of possible loss processes (immobilization, leaching, denitrification, and clay fixation) at a time when N uptake rates are relatively low. Rate of N uptake as the corn plant develops is affected by weather, planting date, and time of fertilizer application but is generally greatest between V8 and silking (Russelle et al., 1983). When N fertilizer applications were delayed until V16, the highest rate of N uptake was generally delayed until after silking (Russelle et al., 1983). This would suggest that applying N fertilizer until at least the silking stage may be a reasonable management option.
Most of the research on N application after planting has compared applications at or before planting to sidedress applications at growth stage V8 or earlier. These applications can typically be accomplished with tractor-drawn equipment, whereas later applications require high-clearance vehicles. In many cases, there are no yield differences between preplant and sidedress N applications (Jokela and Randall, 1989; Roth et al., 1995). Sidedress N applications sometimes give small yield increases (Bundy et al., 1992; Reeves and Touchton, 1986; Welch et al., 1971) or small yield decreases (Stecker et al., 1993). However, even when grain yield is not affected, total dry matter production may be reduced with late sidedress N applications (Jokela and Randall, 1989). Delayed N applications may not be appropriate for corn silage production.
Investigation of N applications later than the V8 growth stage has been limited. The studies that have been conducted have been confined mostly to irrigated systems. Irrigation presents a readily available delivery system for N at stages later than V8 and also creates risk that N fertilizer will be leached out of the root zone, especially on sandy soils.
For irrigated corn grown on sandy soils, sidedress applications tend to produce higher yields than preplant applications (Bundy et al., 1983; Rehm and Wiese, 1975). Supplemental N applications later than normal sidedress time can produce yields higher than those obtained with preplant or sidedress applications alone (Evanylo, 1991; Gascho et al., 1984; Rehm and Wiese, 1975). Jung et al. (1972) observed equivalent yields when a single N application was made from 5 to 8 wk after planting, but yields began to decline when N application was delayed until the ninth week or later. They did not report growth stages, but 5 to 8 wk after planting is likely to correspond to the V5 to V12 growth stages.
Conclusions are similar for irrigated corn on heavy-textured soils—delaying N applications as late as V16 usually produces yields equivalent to or greater than those with earlier applications. On irrigated silty clay loam soils, Olson et al. (1986) measured higher grain yields (averaged over 15 yr) when N was applied at the 11- to 12-leaf stage than when it was applied at planting, and Russelle et al. (1983) measured higher yields when N was applied at V8 or V16 than when it was applied at planting or V4. In contrast, Binder et al. (2000) found that corn yields declined when N applications were delayed—the earliest stage associated with significant yield reduction was V6 in the first year of the study and VT in the second year.
Late N applications in irrigated systems can be moved into the soil and the root zone by irrigation water. Late N applications in dryland production systems might behave differently, for example, being ineffective when rainfall is limited after N applications. Only a few reports of N applications later than V8 in dryland systems are available. Randall et al. (1997) found equivalent corn yields with all N fertilizer applied at planting or with 30% applied at planting and 70% delayed until V16. Miller et al. (1975) obtained a large yield response to N and equivalent yields regardless of whether N was applied in May, June, July, or a May–June split.
In summary, most trials with N applications later than V8 have found little or no evidence of grain yield reduction with delayed N applications. Jung et al. (1972) observed yield reductions when N applications were delayed until 9 wk after planting on an irrigated sandy soil, and Binder et al. (2000) observed yield reductions when N applications were delayed until V6 to VT, depending on the year.
Very few studies have been conducted with N applications later than V8 under dryland conditions. Our objective was to evaluate the yield impact of delaying N applications for dryland corn until the late vegetative growth stages and as far as silking.
|
MATERIALS AND METHODS |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
|---|
The experimental design was a randomized complete block with four replications. Four hybrids (DeKalb 668, Pioneer 3163, Pioneer 3394, and Ciba 4575) were arranged in a complete factorial design with the N-timing treatments. Reported means for each N-timing treatment are averaged over hybrids.
No-tillage production practices were used. Plots were four rows wide with dimensions of 3 by 7.5 m. Planting population was 60000 seeds ha-1.
Plots were end-trimmed to 6 m long before harvest. The center two rows of each plot were harvested with a plot combine. Yields were corrected to a moisture content of 150 g kg-1.
Yield when N was applied at planting was defined as the standard yield for these experiments. Relative yield for later applications was calculated by dividing mean yield for N applied at a given time by the yield with N applied at planting.
On-Farm Experiments
Experiments were established in production corn fields in Missouri in 1997, 1998, and 1999 with a total of 25 site-years. Experiments were located in all four major corn-producing regions of Missouri (Fig. 1)
and represented a broad cross section of soils, hybrids, climate, and management practices that are typical for corn production in Missouri (Table 1). Our findings should thus apply to a broad population of corn fields in Missouri and potentially to other states with similarities in climate and soils.
|
|
Minolta SPAD 502 chlorophyll meter readings were taken from midway along the uppermost collared leaf each time N was applied. Readings were taken on 10 plants per plot in 10 zero-N plots and in 10 plots that had received a high rate of N (
225 kg N ha-1) at planting. Chlorophyll meter readings were not taken in the two 1999 experiments nor at V14 to V15 in the four 1997 experiments that were fertilized at those times. In both 1997 and 1998, the latest chlorophyll meter readings were taken at V13.
The center two rows of each plot were hand-harvested (1.5 by 6 m). Harvest population was also determined in this area. Grain was shelled and weighed, and grain moisture was determined with a hand-held moisture meter. Yields were corrected to a moisture content of 150 g kg-1.
A quadratic-plateau function was used to describe yield response to N rate at planting and to obtain a plateau yield. Least-squares optimization was performed with PROC NLIN in SAS to obtain these functions. Relative yield was then calculated by dividing mean yield for N applied at a given time by the plateau yield for that experiment. Magnitude of yield response was calculated by subtracting mean yield of the zero-N plots from the mean yield for N applied at a given time.
Linear regression analyses were performed using PROC REG in SAS. Quadratic-plateau and linear-plateau regressions were performed using PROC NLIN in SAS. When time of N application was used as the independent variable in regression analysis, it was defined as the vegetative stage (from 0–15.5), with silking assigned a value of 20 (because there are approximately 20 leaves and silking occurs shortly after the emergence of the last leaf and the tassel). A t-test was used to estimate the probability that mean relative yield = 1.00 for several groups of data with later N application times.
|
RESULTS AND DISCUSSION |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
|---|
When experiments were analyzed individually using linear regression, N application time was a significant (
= 0.05) predictor of yield for two of the three on-station experiments (Locations 1 and 3) and 2 of the 25 on-farm experiments (Locations 26 and 27). In all four experiments with a significant response, yield decreased as N application delay increased. The frequency of yield loss with delayed N application was greater in the on-station experiments because longer delays were included in the experiments. When the latest N application time (silking) was not included in the analysis, N application time was not a significant predictor of yield for any of the on-station experiments.
A similar approach was used to examine the possibility that delaying N applications would delay development and result in increased grain moisture at harvest. Regression of grain moisture against time of N application was significant ( = 0.10) at only one location, suggesting that N timing had a minimal effect on grain moisture.
When data from all 28 experiments are pooled, there is little evidence of yield reductions when N applications were delayed as late as growth stage V16 (Fig. 2) . Linear regression analysis did not indicate a significant trend in relative yield when N was applied between planting and V16 for all sites (P = 0.72) or for responsive sites only (P = 0.63) (Fig. 2b). Neither was linear regression significant (P = 0.23) with data from N applications at silking included.
|
Many observations of relative yield deviated substantially from 1.00 (Fig. 2). We don't know whether these deviations are purely experimental error (most data points represent mean yield of only three plots), or whether there is a balance between true yield increases and yield decreases as N applications are delayed. Lower variance of relative yield with N applications at planting (Fig. 2) suggests the latter. However, the standard deviation of relative yield for nonresponsive locations is 0.055, and for responsive locations, it is 0.062 (excluding data from N applications at silking) (Fig. 2). Because the standard deviation of relative yield for nonresponsive locations should represent pure experimental error with no treatment effect, these values suggest that most of the variability in relative yield of responsive locations is due to experimental error rather than treatment effects.
Another way to examine the data is to use t-tests. At growth stages V12 and later, more data points in Fig. 2 are below 1.00 than are above it. A t-test shows that there is a high probability of a true yield reduction (P = 0.012 for H0: relative yield = 1.00) for all N applications delayed until V12 or later. The mean relative yield for these data is 0.95. If only data for N applications from V12 to V16 are considered, P = 0.042 and mean relative yield is 0.97. Mean relative yield when N was applied at silking was 0.85, with values of 0.71, 0.89, and 0.95 for the three experiments receiving N applications at silking.
Overall, our data suggest that risk of a small but real yield reduction occurs when N applications are delayed until the range V12 to V16 and that the risk and the yield reduction are larger when N applications are delayed until silking. We found little or no evidence of irreversible yield loss when N applications were delayed as late as stage V11. This agrees with the findings of Olson et al. (1986), Russelle et al. (1983), and Jung et al. (1972) but contrasts with one of the site-years of Binder et al. (2000) where yield losses were observed when N applications were delayed only until V6. Though full yield was not achieved in our experiments when N applications were delayed until silking, yield was still highly responsive to N application at this stage—yield response exceeded 2.2 Mg ha-1 in all three experiments.
A N rate of 225 kg N ha-1 was sufficient to maximize yield at all locations except one. Data from Location 21 are not included in any of the figures or collective statistical analyses. The soil at this location was poorly drained, and approximately 30 cm of precipitation fell during May and June, resulting in apparently severe denitrification loss of N. Yield response to N applied at planting was linear up to 335 kg N ha-1, the highest N rate applied, so calculating relative yield from the 225 kg N ha-1 applications at different timings was problematic. Regression of yield vs. N application time (from planting to V12) for 225 kg N ha-1 was not significant at this location. Average yield response to 225 kg N ha-1 was 4.2 Mg ha-1.
Yield and Yield Response as a Function of Nitrogen Stress
Binder et al. (2000) report that yield losses with delayed N applications could be predicted by both application timing and the magnitude of N stress that the crop was experiencing at the time of the delayed application. They used relative chlorophyll meter reading (the reading of unfertilized plots divided by the reading from well-fertilized plots) as their measure of N stress. In 22 experiments for which we have chlorophyll meter data (from V5.5 to V13 only), neither N application timing, relative chlorophyll meter reading, their squares, or their cross product is a significant predictor of relative yield in a regression model. Sometimes real effects are lost in a coarse model like this, so we examined finer subsets of data. When grouped by stage of N application, there is little indication that relative chlorophyll meter reading is useful for predicting relative yield (Fig. 3)
. Similarly, when data are grouped by N stress, as indicated by relative chlorophyll meter reading, there is little evidence that delaying N application reduces yield at any stress level (Fig. 4)
.
|
|
While relative chlorophyll meter readings were not useful for predicting the magnitude of irreversible yield loss in these experiments, they were useful for predicting the magnitude of yield gain in response to N application (Fig. 5) . This supports earlier research documenting that chlorophyll meters can be useful for predicting response to N (Piekielek and Fox, 1992). Although relative chlorophyll meter readings sometimes varied substantially over time within an experiment, this variation did not correspond to differences in relative yield or yield gain to N applied at these times within a location. The significant relationship that we observed between relative chlorophyll meter reading and yield gain was the result of differences between locations, rather than between times within a location.
|
0.95 has been suggested as indicating N deficiency and a high likelihood of yield response to additional N fertilizer (Varvel et al., 1997). While relative chlorophyll meter readings were generally high in the six nonresponsive site-years, we observed values of 0.95 in 5 of 17 samplings. The lowest value observed was 0.93. Five of the six nonresponsive site-years had received manure applications, so manure N mineralization after chlorophyll meter readings may account for the lack of yield response. Relative chlorophyll meter reading was not necessarily consistent over time at a given location, but for our full data set, there was no evidence (P = 0.91) that relative chlorophyll meter reading tended to increase or decrease as the season progressed. Thus, a reading at any given time may represent an equally valid snapshot of crop N status. There was weak evidence that relative chlorophyll meter reading decreased over time for 1997 data (P = 0.15) and increased over time for 1998 data (P = 0.09). This may indicate that weather plays a role. Relatively wet weather around V6 in 1998 led to greater apparent N stress and lower relative chlorophyll meter readings than in 1997 at the same stage. This stress may have lessened as soils dried and mineralization resumed.
Extrapolation of Our Results to Other Environments
Climate may affect the relative risk of yield loss with delayed N applications. Reduced early season growth, as might be expected with delayed N applications, might be expected to have less effect in areas with longer growing seasons. Yield losses recorded in the literature in association with delayed N are too few to evaluate this idea, but the observation of Russelle et al. (1983) that delayed N gave more favorable results with early planted than late-planted corn would tend to support it. It may also help to explain the attainment of full yield in Kentucky (Miller et al., 1975) with N applications to severely N-stressed corn at tasseling while we generally observed yield reductions in central Missouri when applications were delayed that long.
Concern is sometimes expressed that late N applications will not be effective in dry weather due to positional unavailability. Most of our 1997 experimental locations had <3 cm of rain in July and experienced considerable water stress. Nine of these experiments received surface N applications in July (as late as 9 July) that produced yields as high as those with earlier applications.
|
SUMMARY |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
|---|
|
ACKNOWLEDGMENTS |
|---|
|
NOTES |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
|---|
|
REFERENCES |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  G. Q. Zhao, B. L. Ma, and C. Z. Ren Response of Nitrogen Uptake and Partitioning to Critical Nitrogen Supply in Oat Cultivars Crop Sci., May 11, 2009; 49(3): 1040 - 1048. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. A. Ruiz Diaz, J. A. Hawkins, J. E. Sawyer, and J. P. Lundvall Evaluation of In-Season Nitrogen Management Strategies for Corn Production Agron. J., November 7, 2008; 100(6): 1711 - 1719. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W. R. Raun, J. B. Solie, R. K. Taylor, D. B. Arnall, C. J. Mack, and D. E. Edmonds Ramp Calibration Strip Technology for Determining Midseason Nitrogen Rates in Corn and Wheat Agron. J., June 16, 2008; 100(4): 1088 - 1093. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Zhang, A. M. Blackmer, J. W. Ellsworth, and K. J. Koehler Sensitivity of Chlorophyll Meters for Diagnosing Nitrogen Deficiencies of Corn in Production Agriculture Agron. J., May 7, 2008; 100(3): 543 - 550. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Zhang, A. M. Blackmer, J. W. Ellsworth, P. M. Kyveryga, and T. M. Blackmer Luxury Production of Leaf Chlorophyll and Mid-Season Recovery from Nitrogen Deficiencies in Corn Agron. J., May 7, 2008; 100(3): 658 - 664. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. A. Hawkins, J. E. Sawyer, D. W. Barker, and J. P. Lundvall Using Relative Chlorophyll Meter Values to Determine Nitrogen Application Rates for Corn Agron. J., June 5, 2007; 99(4): 1034 - 1040. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. L. Ma, K. D. Subedi, and T. Q. Zhang Pre-Sidedress Nitrate Test and Other Crop-Based Indicators for Fresh Market and Processing Sweet Corn Agron. J., January 1, 2007; 99(1): 174 - 183. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. B. Jaynes and T. S. Colvin Corn Yield and Nitrate Loss in Subsurface Drainage from Midseason Nitrogen Fertilizer Application Agron. J., October 3, 2006; 98(6): 1479 - 1487. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. K. Teal, B. Tubana, K. Girma, K. W. Freeman, D. B. Arnall, O. Walsh, and W. R. Raun In-Season Prediction of Corn Grain Yield Potential Using Normalized Difference Vegetation Index Agron. J., October 3, 2006; 98(6): 1488 - 1494. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. C. Scharf, S. M. Brouder, and R. G. Hoeft Chlorophyll Meter Readings Can Predict Nitrogen Need and Yield Response of Corn in the North-Central USA Agron. J., May 3, 2006; 98(3): 655 - 665. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. L. Ma, K. D. Subedi, and C. Costa Comparison of Crop-Based Indicators with Soil Nitrate Test for Corn Nitrogen Requirement Agron. J., March 1, 2005; 97(2): 462 - 471. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K. D. Subedi and B. L. Ma Nitrogen Uptake and Partitioning in Stay-Green and Leafy Maize Hybrids Crop Sci., February 23, 2005; 45(2): 740 - 747. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Crop Science | Vadose Zone Journal | |||
| Journal of Natural Resources and Life Sciences Education |
Soil Science Society of America Journal | ||||
| Journal of Plant Registrations | Journal of Environmental Quality |
The Plant Genome | |||
