Late Season Application of Nitrogen in Virginia Corn Production Systems

By

Robert Trent Jones

Major Project/ Report submitted to the faculty of

Virginia Polytechnic Institute and State University for

Partial Fulfillment of the requirements for the degree of

Online Master of Agricultural and Life Sciences

In

Plant Science and Pest Management

Wade Thomason, Chair

Mark Reiter

David Holshouser

December 20, 2019

ii

Late Season Application of Nitrogen in Virginia Corn Production Systems

Abstract

Agriculture is a leading industry in the state of Virginia producing an economic impact of $70

billion annually in the state. A portion of Virginia’s agricultural industry is driven by the

production of corn, soybean, and wheat crops in rotation. In 2019, as market prices for those

commodities remain weak, farmers must evaluate the feasibility of implementing innovative

technologies and practices in their growing systems in order to improve their production

efficiency. This paper evaluates nitrogen application strategies at the developmental stages when

nitrogen inputs have the greatest positive impact on yield. Specifically, this paper reviews

several studies that have assessed delayed application of sidedressed nitrogen to corn until later

physiological developmental stages in order to determine if this practice would be a good option

for producers who want to increase their production efficiency. This review confirms that

nitrogen plays an important role in crop development and rate and timing of nitrogen application

can significantly influence crop yield. Though it is apparent nitrogen has a major impact on yield

potential, no definite conclusion can be drawn from the studies reviewed here that directly relate

the application of nitrogen past the V10 developmental growth stage to statistically significant

positive yield increase. Of five Virginia study locations reviewed, evaluating application of

additional nitrogen at V12-VT only one location found a statistically significant yield increase of

1082.74 kg ha-1 (16.1 bu/a). Additionally, delaying nitrogen sidedress applications up to V10 did

not negatively impact corn yield in studies conducted in Missouri and Oklahoma, indicating that

a later sidedress window may be considered by Virginia corn growers. While there is no

conclusive evidence that suggests yield will reliably increase when N applications are made later

in the season, other benefits of late season application were identified in this review.

Supplemental benefits include the ability to make fertilizer application decisions based on plant

tissue and soil diagnostic testing completed during the growing season, the ability to spread

workload throughout the growing season, and reduced potential for nitrogen lost to the

environment.

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Table of Contents

Abstract ........................................................................................................................................... ii

Table of Contents ........................................................................................................................... iii

List of Tables ...................................................................................................................................1

List of Figures ..................................................................................................................................2

Introduction ......................................................................................................................................3

Literature Review.............................................................................................................................8

Evaluation of Timing and Rates for Nitrogen Application for Optimizing Maize

Growth and Development and Maximizing Yield ...............................................................8

Corn Yield Response to Nitrogen Fertilizer Timing and Deficiency ................................10

Effect of Delayed Nitrogen Fertilization on Corn Grain Yields ........................................12

2016 Virginia On-Farm Corn Test Plots - 2016 Evaluation of Late Season

Nitrogen Application on Corn ...........................................................................................14

Conclusions ....................................................................................................................................17

Literature Cited ..............................................................................................................................21

Tables .............................................................................................................................................24

Figures............................................................................................................................................26

1

List of Tables

Table 1. Treatment structure for experiments conducted at Efaw, Lake Carl Blackwell, and

Haskell, OK 2005-2006

Table 2. Treatment parameters and mean grain yields and SED’s for experiments conducted at

Efaw, Lake Carl Blackwell, and Haskell, OK 2005-2006

Table 3. Evaluation of late season nitrogen application on corn – Results from locations 1-5

2

List of Figures

Figure 1. US corn grain yield trends since 1866

Figure 2. US corn prices – 10-year historical chart

Figure 3. Illustration of pop-up and starter fertilizer placement for corn

Figure 4. Yield of corn in continuous corn (CC) and corn following soybean (SC) across time

with multiple rates of actual N fertilizer applied

Figure 5. Nitrogen cycle: Transformations between N forms

Figure 6. Total maize N uptake and partitioning across four plant stover fractions: leaf, stalk,

reproductive, and grain tissues. Each value is a mean of six hybrids across two site-years at

Urbana, IL (2010) and DeKalb, IL (2010). GGDF = growing degree days (Fahrenheit)

Figure 7. Photosynthetic rate of corn over time, days after planting

Figure 8. Yield response of corn to treatments and N application rates T1, T2, and T3. Where

Treatment 1 (T1) applied 1/3 N at seedbed preparation, 1/3 N at V6, and 1/3 N at VT. Treatment

2 (T2) applied 1/3 N at V2, 1/3 N at V16, and 1/3 N at R1. Treatment 3 (T3) applied 1/3 N at seed

bed preparation, 1/3 N at V12, and 1/3 N at R2.

Figure 9. Relative yield as a function of timing of a single N application to corn

3

Introduction

The Virginia Department of Agriculture and Consumer Services reports that agriculture serves as

the state of Virginia’s largest industry with an economic impact of $70 billion annually,

employing more than 334,000 residents in the commonwealth (VDACS, 2019). VDACS reports

that 43,225 farms cover 3.2 million ha (7.8 million acres) of land across the state producing a

diverse mix of agricultural products (VDACS, 2019).

A portion of Virginia’s agricultural industry involves the production of corn, soybean, and

wheat. Row cropping in Virginia typically involves a two-year rotation of corn, soybean, and

wheat crops. This rotation allows producers the ability to harvest three marketable crops within a

two-year period on a single parcel of land. The majority of corn planting begins in early April,

after the planting region’s average last frost date, and when soils have reached temperatures

adequate for seed germination. Corn is then harvested in the fall, and wheat is planted. Wheat

overwinters and is harvested the following June, at which point the soybean crop is planted.

Soybean harvest begins in late fall and continues into early winter, ending the two-year crop

cycle which begins again with corn planting the following spring. The 2017 United States

Agricultural Census conducted by the United States Department of Agriculture’s National

Agricultural Statistical Service reported that the state of Virginia produced 1.7 Mg (25,672,603

bu) of soybeans on 243,000 ha (600,310 ac), 3.4 million Mg (53,849,390 bu) of corn on 152,000

ha (378,073 ac), and 673,000 Mg (10,011,616 bu) of wheat on 61,000 ha (151,869 ac) of land in

2017 ranking Virginia 32nd in state grain sales in the United States (NASS, 2017).

Illustrated in Figure 1, average corn grain yields have increased linearly since the late 1930’s

(Nielson, 2017). This steady increase in average yield can be attributed to a number of variables

that affect U.S. corn production. As observed in Figure 1 corn yields were fairly stagnant until

4

the latter half of the 1930’s. At that time, yields had consistently averaged 1.5 to 2 Mg ha-1 (25-

30 bu ac-1) for a number of years. Corn yields began to increase in the late 1930’s as American

corn producers began to rapidly adopt double-cross corn hybrids. This adoption resulted in 50 kg

ha-1 (0.8 bu ac-1 year-1) yield improvement between 1937 and 1955 (Nielson, 2017). Annual

average corn yield improvements were again bolstered in the 1950’s as crop genetics advanced,

and producers increasingly adopted the use of nitrogen fertilizers, synthetic pesticides, and

advanced mechanization. These adoptions increased annual yield improvements to 120 kg ha-1

year-1 (1.9 bu ac-1 year-1) since the 1950’s. Since that time improved plant genetics, crop

production technologies, and production management practices can be credited with the

maintenance of yield improvements in the United States (Nielson, 2017).

Figure 2. illustrates market prices for corn in the United States over the past 10 years. In July

2012, corn prices reached a high of $318 Mg-1 ($8.24 bu-1) (Macrotrends, 2019). Since that time

market prices have been in decline. In order to maintain profitability when markets are not

favorable, producers must compensate by increasing their yields through increased production

efficiency. On-farm production efficiency is improved through the increase of output, in this case

crop yield, without the increase of input and cost. Or a reduction in input cost with no change in

yield.

Corn production in Virginia requires a number of inputs from the producer. Soil fertility is a

major component in producing a crop. Producers will typically address pH and fertility issues

prior to planting. This process begins with soil testing, performed to assess soil pH and nutrient

levels and identify amendments that should be added to replace depleted soil nutrients. In

Virginia, the majority of grain is produced using a no-till system. No-till corn production

provides several benefits to the farmer including reduced erosion, improved water holding

5

capacity, and increased organic material within the field (Thomason et al., 2019). The

implementation of no-till production however, does involve another costly input for the farmer.

Since weed control through tillage is not practiced in no-till, farmers must rely heavily on

herbicides to control weeds. Prior to planting, farmers apply herbicides to provide a weed-free

environment in which germinating crop seeds do not have to compete with weeds. At planting,

farmers use no-till planters to cut through the layer of plant residue on top of the soil in order to

place seeds in adequate contact with soil. Typical seeding rates range from 60,000 to 80,000

seeds ha-1 (24,000 to 33,000 plants ac-1) depending on a number of field and management

parameters. These parameters include historic yield potential, probability of adequate water

availability, soil type, nutrient availability, and individual risk (Carroll, 2014). At planting some

producers apply starter, and or “pop-up” fertilizers with the goal of enhancing early season

seedling growth (Alley et al., 2018). Both starter and pop-up fertilizers are composed of varying

compositions of nitrogen, phosphorus, potassium and occasionally secondary and micronutrients.

As illustrated in Figure 3, pop-up fertilizer is typically placed in the furrow along with the seed

while starter fertilizer is placed a short distance away from the seed (Alley et al, 2018).

Following planting, additional nitrogen applications, known as side dress applications, are made.

Side dress application typically occur at the V4-V6 growth stage of corn with the goal of

supplying necessary nutrients, especially nitrogen and sulfur as the corn ear reaches reproductive

maturity. Fertilizer applications made at multiple points within the growing season, known as

split applications, are made to supply the plant with necessary nutrients to adequately support the

current and future plant nutrient demand. The process of split nitrogen application reduces the

potential for loss of excess nitrogen compared to supplying the nitrogen for the entire season at

planting. Along with nutrient management, producers are faced with crop protection decisions

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throughout the season. Fungicide and insecticide applications are made based on the disease and

insect pressures observed during crop scouting. Application decisions for disease and insect

pressure are typically founded on economic threshold values. Threshold values determine

whether or not the negative yield impact caused by insects or disease warrants the additional cost

of a chemical application to control the insect or disease pressure.

Nitrogen is an essential element for plant growth and reproduction (Sawyer, 2018). Nitrogen is

involved in many important biochemical processes such as photosynthesis and plant components

such as amino acids, proteins, and chlorophyll (Sawyer, 2018). In Virginia, it is assumed that one

pound of nitrogen applied results in one bushel of corn produced. There is no linear relationship

between yield and N rate however (Camberato, 2014). The actual amount of nitrogen utilized

and resulting yield varies depending on environmental circumstances, timing of application,

placement of nitrogen, and hybrid response (Carrol, 2014). Yield increases as nitrogen rates

increase until other limiting factors restrict the plant from producing higher yields (Figure 4). It

can be deduced from Figure 4, that the corn plant does not rely solely on nitrogen fertilization by

the farmer, the corn plant also draws on nitrogen stores in the soil.

In most corn production systems in the Mid-Atlantic Region, 33-45 kg N ha-1 (30 to 40 lb N ac-1)

is applied at or near planting, and the remainder is applied later in the season (Carroll, 2014). The

timing of the second application of nitrogen can affect how quickly the nitrogen is absorbed by

the plant, and plants nitrogen use efficiency. Nitrogen that is not taken up by the plant remains in

the soil and is subject to immobilization or loss through volatilization, denitrification, or leaching

(Figure 5).

Figure 6. depicts corn seasonal nitrogen uptake. Between V9 and tassel, where the slope of the

line is greatest, the corn plant takes up almost 40% of the total seasonal N requirement.

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“Leaching of nitrate out of the root zone and denitrification are processes that cannot be directly

controlled. However, the potential for their occurrence can be reduced by waiting to apply N

until the crop is ready to absorb it, thereby reducing the amount of time that the N sits in the soil”

(Beegle, 2019). Corn producers receive the greatest benefit from nitrogen applications when they

are synchronized with plant demand.

A number of costly inputs are required in order to produce a high yielding corn crop. As

producers are faced with declining crop value, they must adapt by producing higher yields

without increasing the cost of production. This means maintaining current inputs, but managing

them in such a way that provides an increased benefit to the plant, resulting in a higher yield.

The goal of this paper is to evaluate nitrogen application strategies that would provide nitrogen

to corn at stages of development at which nitrogen inputs will have the greatest positive impact

on yield. Specifically, this paper will review studies that evaluate delayed or multiple

applications of side dressed N, and discuss whether these strategies could increase corn yield in

Virginia.

8

Literature Review

Evaluation of Timing and Rates for Nitrogen Application for Optimizing Maize Growth

and Development and Maximizing Yield (Hammad et al, 2018)

This study, conducted in Pakistan’s sandy clay loam soils during the 2009 and 2010 growing

seasons, analyzed the effect of nitrogen application timing and rate on corn yield. Three

treatments were established to apply five N rates. 100, 150, 200, 250, 300 kg ha-1 (89, 134, 178,

223, 267 lb ac-1 respectively). Treatment 1 (T1) applied 1/3 N at seedbed preparation, 1/3 N at

V6, and 1/3 N at VT. Treatment 2 (T2) applied 1/3 N at V2, 1/3 N at V16, and 1/3 N at R1.

Treatment 3 (T3) applied 1/3 N at seed bed preparation, 1/3 N at V12, and 1/3 N at R2.

The corn hybrid Pioneer Brand P31R88 was planted at 66,666 seeds ha-1 (26,990 seeds ac-1) in

all treatments. Crop management practices were standardized in all plots. Per soil test

recommendations, appropriate rates of P2O5 and K2O were applied at seedbed preparation.

Timing of N application was based on visual interpretation of growth stages.

Throughout the growing season, the net photosynthetic rate of corn plants in each treatment was

monitored using a portable infrared gas-analyzer-based photosynthesis system. Plant stover was

collected and analyzed using a modified Kjeldahl digestion method to determine total plant N

content. Nitrogen recovery efficiency (NRE) was calculated using the equation NRE= (Ni-

Nj)/ΔN where “Ni is N uptake in the individual fertilized plots, Nj is N uptake in the treatment

having basal dose of N (100 kg N ha-1), and ΔN is the difference between Ni and Nj.”

Plots were harvested and grain yields were recorded using standardized methods.

Nitrogen application timing significantly impacted the corn plant photosynthetic rate.

Photosynthetic rate decreased when plants had insufficient amounts of nitrogen available to

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them, and the rate increased rapidly when additional nitrogen was applied after periods of deficit

(Figure 7). This rate increased most rapidly at silking, as sucrose and carbohydrates produced

through photosynthesis in the leaves are transferred to the cob for grain production.

Yield results graphed in figure 8 do not trend an expected yield curve. Figure 8 suggests that

applying zero fertilizer would result in greater yields than if 112 kg ha-1 (100 lb ha-1) were

applied. In Figure 8. T2 at the 250 kg ha-1 (223 lb ac-1) rate outperformed all other treatment and

application rate combinations. Overall T2 produced the highest yields across all application rates

followed by T1 and then T3.

Hammad states that the greater yield of T2 is the result of providing nitrogen to plants during

crucial need periods, namely the V2, V16, and R1 growth stages. It is suggested that residual soil

N as well as energy stored in cotyledons provided plants sufficient energy to reach the V2 stage,

at which time additional N was applied. In both T1 and T3 1/3 of N was applied at seedbed

preparation. It is possible that the plant did not need that much N at that time and that some N

was lost through leaching and volatilization since the N need of corn plants during early growth

stages are relatively low. Nitrogen lost to the environment may have resulted in N deficiency that

led to the decreased yields observed in treatments T1 and T3.

In this study, over all treatments, yield began to decrease with application rates greater than 250

kg ha-1 (223 lb ac-1). This suggests that higher yield cannot be obtained indefinitely by simply

applying additional N.

When comparing the three treatments, T3 delayed N application the longest, applying the final

1/3 application of nitrogen at the R2 growth stage. T2 delayed the final N application until the

R1 growth stage. Grain yields of T3 were significantly lower than T2, especially at higher rates

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of N application. Yield differences between the two treatments may be a result of the timing of

earlier N applications, but this may also suggest that N applications after the R1 growth stage do

not positively impact grain yield.

Corn Yield Response to Nitrogen Fertilizer Timing and Deficiency Level (Scharf et al,

2002)

This study was performed with both research station and on farm plots. On-station experiments

were conducted in Missouri between 1995 and 1998, however data recorded in 1997 was

excluded from the results due to severe drought. Plots were designed using four corn hybrids

(Dekalb 668, Pioneer 3163, Pioneer 3394, and Ciba 4575) planted at 60,000 seeds ha-1 (24,290

seeds ac-1), arranged in a complete factorial design with N-timing treatments. In these plots one

application of 180 kg N ha-1 (161 lb ac-1) was applied either at planting, V7, V14 or silking in the

form of ammonium nitrite. Nitrogen was applied by hand, making a special effort to apply below

leaves in order to avoid leaf burn.

On-station plots were all planted using zero tillage in 4 row plots with the dimensions 3 by 7.5

m. Prior to harvest plots were end trimmed to 6 m length. Only the two center rows of each plot

were harvested. For on-station plots, the standard practice yield was the yield measured when all

N was applied at planting. The relative yield of plots that had N applied later in the season was

calculated by dividing mean yield for each treatment by the standard practice yield.

On-farm experiments were conducted in Missouri in 1997, 1998 and 1999. On-farm trials

“represented a broad cross section of soils, hybrids, climate, and management practices”. In these

plots a single application of 225 kg ha-1 (200 lb ac-1) N was applied either at planting, the V6

11

growth stage, or two or three times post V6. Nitrogen application was delayed no longer than

growth stage 15.5 in any plot. Additional on-farm plots received rates ranging from 0 to 335 kg

ha-1 (300 lb ac-1) N at planting. These plots were established in order to determine yield response

to N and verify that the 225 kg ha-1 (200 lb ac-1) rate was sufficient. On-farm plots were planted

in four rows at a length of 12 m. Applications of ammonium nitrate were made at growth stage

V6 using a hand push spreader with drop tubes. Ammonium nitrate applications at later growth

stages were made by hand. Chlorophyll meter readings were taken at each N application time. At

maturity, plots were end trimmed, and the center two rows of each plot were harvested by hand.

Grain was shelled and weighed to determine yield. Using a quadratic-plateau function, a plateau

yield was established from the yield response to N. Relative yield for on-farm plots was

calculated by dividing mean treatment yield by the plateau yield.

In this study, the average yield response to N fertilizer was calculated to be 3.1 Mg ha-1 (1.22 bu

ac-1). This value included plots that were nonresponsive to N application. Overall five out of 28

plots showed no response to N fertilizer. These five plots either had either received manure

earlier in the season, or had high soil nitrogen levels.

In two of the three on-station plots and two of the on-farm experiments, N application timing

was determined to be a significant predictor of crop yield. In these four experiments, as the delay

in nitrogen application increased so did yield loss. This frequency in correlation between timing

and yield was greater in on farm experiments due to the extended application delay until silking,

which was not a treatment in the on-station tests. When treatments, including application delay

until silking, were removed from the analysis, it was determined that nitrogen application timing

was not a significant predictor of yield for any of the three on-station experiments.

12

When observing the regression analysis of all 28 treatments it is apparent that yield loss begins to

occur at V10 and significantly larger losses begin to occur when nitrogen application is delayed

until growth stage V15 (Figure 9). Overall, no irreversible yield loss occurred if N was applied

prior to growth stage V11 in these experiments.

In these experiments, there was no indication that delaying the timing of N application in corn

growing systems will increase yields. However, it is important to take into consideration that

nitrogen applications were made in single sum applications. This means that plants received no

supplemental N until the treatment application was made.

Effect of Delayed Nitrogen Fertilization on Corn Grain Yields (Walsh, 2006)

This study was conducted at three locations in Oklahoma during the growing seasons of 2005

and 2006. Locations involved are referred to in the results as Efaw, Lake Carl Blackwell (LCB),

and Haskell. In this study, 14 combinations of preplant and sidedress N fertilizer application

rates and timings were evaluated to determine their effect on yield. Parameters for nitrogen

application rates and timings for each treatment are located in Table 1.

Prior to planting, soil samples were collected at each site and analyzed for N03-N, NH4-N, total

N, organic C, P, and K in order to characterize a baseline fertility for the sites. In 2005 Pioneer

33B51 was established at the Efaw, and Lake Carl Blackwell, and Triumph 1416Bt was

established at Haskell. In 2005 seeding rates of 59,280 seeds ha-1 (24,000 seeds ac-1) were

established at Efaw and Haskell. Planting population was increased to 74,100 seeds ha-1 (30,000

seeds ac-1) for the Lake Carl Blackwell site in 2005 due to the presence of irrigation. In the 2006

study, Pioneer 33B51 was established at all sites. In 2006, seeding rate was 54,340 plants ha-1

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(22,000 seeds ac-1) at Efaw, 79,040 seeds ha-1 (32,000 seeds ac-1) at Lake Carl Blackwell and

61,750 seeds ha-1 (25,000 seeds ac-1) at Haskell.

In 2005, preplant N fertilizer was broadcast applied in the form of ammonium nitrate (34%N)

and incorporated into the soil at planting. In 2006, instead of ammonium nitrate, urea (46%N)

was soil incorporated for preplant fertilizer application. In both 2005 and 2006 sidedress

applications were made in the form of urea ammonium nitrate (UAN) (28%N) at the base of

plant rows.

The center two rows of each for row plot were harvested and oven dried. Grain weight, total N

content, total N uptake, and nitrogen use efficiency were calculated.

Yield results from the 2005 and 2006 growing seasons are found in Table 2. Lack of

precipitation in 2006 resulted in water stress and higher temperatures that reduced N uptake and

decreased pollination and grain development. The effect environmental conditions have on the

crop are apparent when yield results from 2005 and 2006 are compared. Overall, when N

fertilizer was applied at planting and the second application was applied at V6, yields were

generally higher than other treatments. In most cases, yield increased as N application rate

increased, however at certain locations, significant yield decreases were observed when N was

increased from 90 to 180 kg ha-1 (80 to 160 lb ac-1).

The greatest nitrogen use efficiencies were observed in treatments that received preplant nitrogen

followed by sidedress application that occurred between the V6 and V10 growth stages, followed

by preplant applications, followed by applications after the V10 growth stage.

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2016 Virginia On-Farm Corn Test Plots - 2016 Evaluation of Late Season Nitrogen

Application on Corn (Balderson & Moore, 2016)

This study was an on-farm evaluation of the effects of the addition of late season application of

nitrogen to corn at five locations in Virginia. At location one, 67 kg N ha-1 (60 lb N ac-1) was

applied prior to planting. Corn was planted on April 15, and an additional 112 kg N ha-1 (100 lb

N ac-1) was applied at side dress. On June 16 the field reached the V12 developmental stage and

three late season plots were established on which 34 kg (30 lb) additional nitrogen was applied in

the form of urea. Three check plots on which no additional nitrogen was applied were also

established within the same field. Plots were harvested with commercial equipment on

September 5.

At location two, 20 kg N ha-1 (18 lb N ac-1) was broadcast prior to planting on April 27.

Following planting two separate nitrogen applications were made to the entire field resulting in a

total of 168 kg N ha-1 (150 lb N ac-1) applied. On June 30 at the VT developmental stage, 50 kg

(45 lb) additional N was applied in the form of urea. Three check plots were also established

within the field. Plots were harvested on September 13.

At location three, 4.5 Mg ha-1 (two tons) of poultry litter was incorporated into the soil prior to

planting on April 26. On July 12 at the VT reproductive stage 50 kg (45 lb) additional nitrogen

was applied in the form of urea. Three check plots were established within the same field on

which no additional nitrogen was applied. Plots were harvested on September 15.

At location four, 78 kg N ac-1 (70 lb N ac-1) was broadcast prior to planting on May 24. An

additional 168 kg N ha-1 (150 lb N ac-1) was applied to the entire field as a side dress application.

On June 30 at the VT reproductive stage 50 kg (45 lb) of additional nitrogen were applied in the

15

form of urea. Three check plots were established within the same field on which no additional

nitrogen was applied. Plots were harvested on September 14.

At location five, 90 kg (80 lb) of nitrogen was applied prior to planting on April 20. Following

planting, 123 kg (110 lb) of nitrogen was applied as a side dress application. On June 29 at the

VT reproductive stage, 50 kg (45 lb) additional nitrogen was applied in the form of urea. Three

check plots were established within the same field on which no additional nitrogen was applied.

Plots were harvested on September 13.

At all locations, individual plots were weighed using a weigh wagon. Grain moisture for each

plot was measured using a hand-held moisture meter. Yields for each plot were adjusted to 15.5

g kg-1 moisture.

Location one plots that received an additional 34 kg (30 lb) of nitrogen on June 16 yielded 11.4

Mg ha-1 (182 bu ac-1) and those that did not averaged 11.1 Mg ha-1 (177 bu ac-1), but this

difference was determined to have no statistical significance (Table 1).

Location two plots that received an additional 50 kg (45 lb) of nitrogen at the VT developmental

stage yielded much higher than those that did not receive additional nitrogen (Table 1). On

average, plots that received additional nitrogen on June 30 yielded 11.5 Mg ha-1 (183.5bu ac-1)

while those that did not receive additional nitrogen yielded 10.5 Mg ha-1 (167.4 bu ac-1) a

significant difference.

At location three, plots that received additional nitrogen averaged a yield of 10.7 Mg ha-1 (170.7

bu ac-1) while control plot yields averaged 10.6 Mg ha-1 (170.2 bu ac-1), a non-statistical

difference.

16

At location four, plots that received 50 kg (45 lb) of additional nitrogen on June 30 on average

yielded 14.8 Mg ha-1 (236.1 bu ac-1) while control plots averaged 14.8 Mg ha-1 (231.1 bu ac-1)

(Table 1). There was no statistical difference between treatment and check plot yields.

At location five there was no statistically significant yield difference between plots that received

an additional 50 kg (45 lb) of nitrogen on June 29. Treatment plots averaged 11.0 Mg ha-1 (174.7

bu ac-1) while control plots averaged 10.9 Mg ha-1 (174.3 bu ac-1).

At all five locations at which the 2016 Evaluation of Late Season Nitrogen Application on Corn

work was completed, treatments plots that received additional nitrogen at the VT developmental

stage produced higher average numerical yields than control plots that did not receive additional

nitrogen. However, location two was the only location at which yield increases that resulted from

late season nitrogen application were found to be statistically significant when compared to the

average yield of the control plots.

When the on-farm study performed in Virginia was further reviewed, it was determined that

when comparing treatments at all five locations, N added treatments outperformed their paired

check 8 of 15 times. Further statistical analysis was performed on the 136 kg ha-1 (5 bu ac-1)

average yield difference across all locations to determine at what point the yield difference

would be considered statistically significant. It was determined that when p<0.25 the 136 kg ha-1

(5 bu ac-1) yield increase averaged across all sites would be considered statistically significant.

While additional nitrogen at all five locations was applied as the crop entered the VT

developmental stage, other management practices were not standardized across all five locations.

One of the main differences between location two and the other four locations is the timing and

rate of application of nitrogen. At location two, three nitrogen applications were made prior to

17

the “late season” treatment application. At location two only 20 kg (18 lb) of nitrogen was

broadcast prior to planting, 56 kg (50 lb) was applied with pesticide applications and an

additional 112 kg (100 lb) was applied as a side dress application prior to the 50 kg (45 lb)

applied at the VT growth stage. Locations one, four and five applied much higher rates of

nitrogen prior to planting and locations one, three, and four only applied one additional

application following planting. It is possible that splitting corn nitrogen needs into multiple

applications at location two provided the crop nitrogen as it was needed increasing its use

efficiency response.

Conclusions

From the studies reviewed in this paper, it is apparent that N rate and timing have great influence

over the yield potential of corn plants. Timing of application and the total amount of N applied

throughout a growing season strongly influence potential yield. It should be noted however, that

application timing and total amount of N applied are dependent on one another and a number of

other limiting factors when relating to yield. As made apparent in Hammad et al, (2018), simply

increasing nitrogen application rates will not infinitely increase yield. Though it is apparent

nitrogen has a major impact on yield potential, no definite conclusion can be drawn from the

studies reviewed that directly relates the application of nitrogen to statistically significant

positive yield response. Studies performed by Scharf and Walsh suggest that irreversible yield

loss related to postponing N application does not occur until the V10 developmental growth

stage, however it is not certain that these results will translate to Virginia soils.

18

Of the treatments evaluated in this paper, only location two of “Evaluation of Late Season

Nitrogen Application on Corn” (Balderson & Moore, 2016) reported higher yield supporting the

application of late season nitrogen application in corn. This location was unique when compared

to most other plots evaluated, in that a total of four separate applications of nitrogen were made

throughout the growing season compared to fewer applications made in other plots. By splitting

N application into a total of four applications there was far less likelihood that N would be lost to

the environment. Instead, it was made available to the plant when it was needed. This concept is

supported in Walsh 2006 where further splitting applications of N proved to increase crop yield

when compared to the yields of plots that received single applications of N within a growing

season. Additionally, at location two in Balderson & Moore’s study, a much lower rate of

nitrogen was applied at planting compared to other treatments examined. Because plant nitrogen

needs are smaller in early developmental growth stages, greater N rates at planting and fall are

more prone to environmental loss. This is supported by Hammad’s treatment T2 where no

nitrogen was applied until the V2 developmental growth stage. Hammad suggests that the

seedlings are able to sustain themselves entirely on soil stores and the energy stored in

cotyledons until V2 application was made.

Numerous factors work together to influence crop yield. It is expected that response to late

season application of N would be greater in plots that do not receive high rates of N early in the

season, when organic nitrogen levels within fields are low, and when the growing system itself

has high yield potential without limiting factors. In the Virginia on-farm study locations one,

two, and three each received lower rates of N early in the season when compared to locations

four and five. Location two however, is the only location that resulted in a statistically significant

yield difference. It is possible that locations two and three did not respond to the application of

19

additional N later in the season as a result of other required factors being absent within the field.

Locations four and five were less likely to respond to late season treatment because they received

higher rates of N earlier in the season that were able to sustain the plant throughout the growing

season.

Averaging yield results from all five locations in “Evaluation of Late Season Nitrogen

Application on Corn” (Balderson & Moore, 2016) treatments that received additional nitrogen

later in the season averaged 12.7 Mg ha-1 (189.4 bu ac-1), and treatments that did not receive

additional nitrogen averaged 12.4 Mg ha-1 (184.0 bu ac-1). Resulting in a 363.2 kg ha-1 (5.4 bu ac-

1) increase when additional N was applied. Using the 2019 average corn market closing price of

$3.85, plots that received additional N generated $20.79 per acre. With N costs averaging $0.50

per pound, additional application of 50 kg N ha-1 (45 lb N ac-1) would cost $22.50. Without

considering labor, and application cost, under these conditions, the additional application of 50

kg N ha-1 (45 lb N ac-1) would not be profitable until prices reached $4.17 per bushel.

Location two of “Evaluation of Late Season Nitrogen Application on Corn” (Balderson &

Moore, 2016) reported average yields of 12.3 Mg ha-1 (183.5 bu ac-1) in plots that received an

additional 50 kg N ha-1 (45 lbs N ac-1) and 11.3 Mg ha-1 (167.4 bu ac-1) in plots that did not. A

statistically significant difference of 1082 kg ha-1 (16.1 bu ac-1). At location two additional N

application resulted in additional revenue of $61.99 per acre. This additional revenue covers the

$22.50 cost of N as well as cost of labor and application.

While there is no conclusive evidence that suggests yield will be consistently increased when N

applications are made later in the season, other benefits of late season application were identified

in this review. Additionally, it was determined that delaying nitrogen sidedress applications up to

V10 did not negatively impact corn yield in Missouri and Oklahoma. Though results may not

20

translate to Virginia soils, supplement benefits may be considered by Virginia corn growers.

When nitrogen is applied in several smaller applications throughout the growing season as it is

needed by the plant, as opposed to one or two lump sum applications, the plant readily absorbs

the nutrient. This reduces the potential for negative impacts associated with nitrogen lost to the

environment. Additionally, further splitting N application allows the producer the opportunity to

monitor their crop in season to determine the plants actual needs and address those needs with

accurate N applications later into the growing season. Finally, splitting nitrogen applications later

in the season allows producers to spread their work load to a period when other work

requirements are not as high.

In Virginia, irrigation of corn is not common so if late season application of nitrogen is to be

explored further with the intent of application in actual production scenarios, fertigation is not a

likely delivery option. Instead, nitrogen delivery methods such as aerial application, or ground

applications with high clearance vehicles should be considered as corn plants are too tall to make

N applications with normal equipment without significantly damaging the crop.

Ultimately producers must decide if potential yield increases, the ability to assess plant needs

within the growing season, the spread of work load throughout the season, and reduced negative

environmental impact are enough of a benefit to further split applications of nitrogen into later

crop physiological growth stages beyond what is current common practice. Growers should use

the information compiled here, as well as in other replicated studies to make individual decisions

about the adoption of late season N application based on specific cost of implementation and

perceived return on investment.

21

Literature Cited

Alley, Mark, Reiter, Scott, Thomason, Wade, Reiter, Mark. Pop-up and/or Starter Fertilizers for

Corn. Virginia Cooperative Extension, 2018,

www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/3002/3002-1438/SPES-77.pdf.

Balderson, Keith, and Moore, David. “2016 Evaluation of Late Season Nitrogen Application on

Corn.” 2016 Virginia On-Farm Corn Test Plots, Virginia Cooperative Extension, 2016,

www.sites.ext.vt.edu/newsletter-archive/corn-test-plots/2016.pdf

Beegle, Douglas. Nitrogen Fertilization of Corn. PennState Extension, 2019,

extension.psu.edu/nitrogen-fertilization-of-corn.

Bender, Ross R, Haegele, Jason W, Ruffo, Matias L, Below, Fred E. “Modern Corn Hybrids’

Nutrient Uptake Patterns.” Better Crops, vol. 97, no. 1, 2013, pp. 7–10.

Camberato, Jim, and Nielsen, Robert. “Applied Crop Research Update.” Applied Crop Research

Update, Purdue University Department of Agronomy, Mar. 2019,

https://www.agry.purdue.edu/ext/corn/news/timeless/NitrogenMgmt.pdf.

Carroll, Mike. Keys to Successful Corn Production. North Carolina Cooperative Extension,

2014, craven.ces.ncsu.edu/keys-to-successful-corn-production/.

Hammad, Hafiz Mohkum, Abbas, Farhat, Ahmad, Ashfaq, Farhad, Wajid, Wilkerson, Carol Jo,

Hoogenboom, Gerrit. “Evaluation of Timing and Rates for Nitrogen Application for

Optimizing Maize Growth and Development and Maximizing Yield.” Crop Ecology and

Physiology, vol. 110, no. 2, 1 Mar. 2018, pp. 565–571.

22

International Plant Nutrition Institute, “The Nitrogen Cycle.” Plant Uptake and Removal Image

Database, 2019.

John E Sawyer. Nitrogen Use in Iowa Corn Production. Iowa State University, March 2018,

store.extension.iastate.edu/Product/Nitrogen-Use-in-Iowa-Corn-Production.

Larson, Erick, Golden, Bobby, Oldham, Larry. How to Get the Best Return on Your Corn

Nitrogen Dollars. Mississippi State Univeristy, 5 May 2016, www.mississippi-

crops.com/2016/05/05/how-to-get-the-best-return-on-your-corn-nitrogen-dollars/.

Macrotrends. Corn Prices - 10 Year Historical Chart. 2019, www.macrotrends.net/2532/corn-

prices-historical-chart-data.

Nielson, Robert L. “Historical Corn Grain Yields for the U.S.” Corny News Network, Purdue

University, May 2017, www.agry.purdue.edu/ext/corn/news/timeless/YieldTrends.html.

Sawyer, John E. Iowa State University Extension and Outreach, Mar. 2018,

https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcseprd355421.pdf.

Scharf, Peter C,Wiebold, William J., Lory, John A. “Corn Yield Response to Nitrogen Fertilizer

Timing and Deficiency Level.” Agronomy Journal, vol. 94, no. 3, May 2002.

Thomason, Wade E, Youngman, Rod E, Hagood, E Scott, Stromberg, Erik L, Alley, Mark M,

Wyser W.G. Successful No-Tillage Corn Production. Virginia Cooperative Extension,

2019, www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/424/424-030/424-030.pdf.

USDA, National Agricultural Statistics Service. “State Summary Highlights: 2017.” 2017

Census of Agriculture - State Data, USDA, National Agricultural Statistics Service,

23

2018,www.nass.usda.gov/Publications/AgCensus/2017/Full_Report/Volume_1,_Chapter

_2_US_State_Level/st99_2_0001_0001.pdf.

Walsh, Olga, Raun, William, Klatt, Arthur, Solie, John B, Emslie, A Gordon. “Effect of Delayed

Nitrogen Fertilization on Maize Grain Yields and Nitrogen Use Efficiency.” Journal of

Plant Nutrition, vol. 35, no. 4, 3 Feb. 2012, pp. 538–555.,

doi:10.1080/01904167.2012.644373

Virginia Department of agriculture and Consumer Services. “Virginia Agricultural Facts and

Figures.” Agricultural Facts and Figures, Virginia Department of Agriculture and

Consumer Services, 2019, www.vdacs.virginia.gov/markets-and-finance-agriculture-

facts-and-figures.shtml.

24

Table 1. Treatment structure for experiments conducted at Efaw, Lake Carl Blackwell, and

Haskell, OK 2005-2006

Source: Walsh, 2006

Table 2. Treatment parameters and mean grain yields and SED’s for experiments conducted at

Efaw, Lake Carl Blackwell, and Haskell, OK 2005-2006

Source: Walsh, 2006

25

Table 3. Evaluation of late season nitrogen application on corn – Results from locations 1-5

Location

N applied Prior to

Treatment

Establishment

Additional N

Applied to

Treatments

(lbs.)

Average

Treatment

Yield (bu/a)

Average

Untreated

Yield (bu/a)

Statistically

Significant

1 160 lbs. 30 182.0 187.0 No

2 168 lbs. 45 183.5 167.4 Yes

3 2 Tons Poultry Litter 45 170.7 170.2 No

4 220 lbs. 45 236.1 231.1 No

5 190 lbs. 45 174.7 174.3 No

Source: Balderson & Moore, 2016

26

Figure 1. US corn grain yield trends since 1866

Source: Nielson, 2017

Figure 2. US corn prices – 10 year historical chart

Source: Macrotrends, 2019

27

Figure 3. Illustration of pop-up and starter fertilizer placement for corn

Source: Alley et al, 2018

Figure 4. Yield of corn in continuous corn (CC) and corn following soybean (SC) across time

with multiple rates of actual N fertilizer applied

Source: Sawyer, 2018

28

Figure 5. Nitrogen Cycle: Transformations between N forms

Source: International Plant Nutrition Institute, 2019

Figure 6. Total maize N uptake and partitioning across four plant stover fractions: leaf, stalk,

reproductive, and grain tissues. Each value is a mean of six hybrids across two site-years at

Urbana, IL (2010) and DeKalb, IL (2010). GGDF = growing degree days (Fahrenheit)

Source: Bender et al, 2013

29

Figure 7. Photosynthetic rate of corn over time, days after planting

Source: Hammad et al, 2018

30

Figure 8. Yield response of corn to treatments and N application rates T1, T2, and T3. Where

Treatment 1 (T1) applied 1/3 N at seedbed preparation, 1/3 N at V6, and 1/3 N at VT. Treatment

2 (T2) applied 1/3 N at V2, 1/3 N at V16, and 1/3 N at R1. Treatment 3 (T3) applied 1/3 N at seed

bed preparation, 1/3 N at V12, and 1/3 N at R2.

Source: Hammad et al, 2018

Figure 9. Relative yield as a function of timing of a single N application to corn

Source: Scharf et al, 2002