Nitrogen Recalibration for Corn in North Dakota

Introduction-
This is a summary of the first year of field N rate experiments for corn to support a review and possible revision of current corn N recommendations. The objective is to gather corn yield data from N rate experiments over a large number of environments, mostly on grower fields, and use that data and ancillary data from relevant adjoining state regions to develop recommendations that will increase corn grower profitability in North Dakota.

Methods-
Nearly all sites conformed to similar protocols. The sites were in fields that were going to be planted to corn. The previous crop was noted, and the sites sampled to make sure that the residual nitrate was low enough for supplemental N to have some yield effect. The experimental design was a randomized complete block with 6 treatments (check, 40 lb N, 80 lb N, 120 lb N, 160 lb N and 200 lb N) with four replications. Each individual plot was 8-10 feet wide and 20 feet long, with a 5-foot alleyway between blocks. In most cases, the experimental plots were staked, the N treatments were applied (at Franzens sites with ammonium nitrate 34-0-0, at Ashley and Endres sites with urea) before grower tillage. The site corners were georeferenced with a GPS receiver and large metal washers were buried at the corners about 4 inches deep. The internal flags marking individual plots were removed, but large, 4 foot tall orange/red flags were left at the corners (with about a 10 foot buffer) to let the grower directed N applicator know where not to apply N fertilizer. After the field was fertilized and worked (in the conventionally tilled fields) the field was planted by the grower including the plot area. Any row starter of other fertilizer applied to the experimental plots was noted and the N it included was added to the known available N for the plots. When the plots were in an annual legume, such as soybean of dry bean, a 40 lb N credit was added to the known available N. After the corn emerged, the individual plot flags were again installed, using the corners as reference to the plot edges. When the corn was in about the 8 -12 leaf stage, a Greenseeker ® sensor was used over each plot in the 16 most eastern experiments. The results of the sensor readings, in relation to available N, are included in this report. Alleyways and access to the plots from the road were mowed or hoed at this time. An additional alleyway cleaning was required at most sites in mid-August. One interior row was hand-harvested. The ears were collected in a bag designated for the plot and carried to the field edge for transport back to campus. The ears were dried to about 10% moisture, and then shelled. The grain was weighed for yield, along with its moisture content and test weight.

Results and notes from individual experiments-

Sargent County-
This site was located at about 45^o 58.82’ north latitude, 97^o 26.9’ west longitude, southeast of Rutland, ND. The soil is an Overly silt loam (fine-silty, mixed, superactive, frigid, Pachic Hapludolls).The field was in wheat stubble, with a cover crop of forage radishes/turnips seeded directly after wheat harvest in fall 2009. The cover crop was grazed in the fall. Residual N as nitrate was 68 lb/acre to a 2 foot depth, P was 10 ppm. Soil pH was 7.8, Zn was 2.2 ppm, K was 340 ppm. OM was 6.8%. This field was tiled and has been in long-term (longer than 6 years) no-till or modified no-till. The field was spring strip-tilled after the experiment treatments were applied with 100 lb/acre of 10.5-46-3.5-1, for an additional 10.5 lb/acre of N. Corn variety was Pioneer Hi-Bred 38A56 seeded at 34,000 seeds/acre on 5/3. Harvest stand was about 34,800 plants/acre in 20 inch rows.
The corn was too tall to evaluate the Greenseeker at this site.

Table 1. Corn yield with N rate treatment at Rutland

Treatment, lb N/acre	Yield, bu/acre	Test Weight, lb/bu
Check	172	57.6
40	187	57.7
80	189	57.8
120	189	57.0
160	188	57.4
200	198	57.8
F	0.78	1.01
P	0.58	0.44
LSD	NS	NS

Figure 1. Although the relationship of yield to known available N shows a trend, it is not significant and the best summary would be to state that the study averaged about 188 bu/acre with no added N.

The analysis of these data show there was no response to N. If an additional 50 lb N/acre was added to the 68 lb residual N from the soil test, the 10 lb N from the strip-till P application, and the 50 lb N from long-term no-till, because of the OM being above 5.9%, that would provide a total of 178 lb total known N to the check plot, or about 1 lb N per productive bushel. This is close, and perhaps a little below the eastern plot average of about 1.1 lb N per productive bushel. The cover crops may have helped to improve the efficiency of N in this plot.

Barnes County
These two sites were located very close to each other about 5 miles SE of Valley City, ND on a Renshaw sandy loam, fine-loamy over sandy or sandy-skeletal, frigid Typic Calciaquolls. The field was in spring wheat the previous year and has been in no-till continuously for about 20 years. The residual N at site one was 51 lb N/acre to a 2 foot depth, P was 19 ppm, Zn 1 ppm, K 130 ppm, pH 6.2, OM 3.3%. Residual N at site 2 was 53 lb/acre, P was 17, Zn was 0.9, K was 115 ppm, pH was 5.8 and OM was 4.2%. The corn variety was Pannar 2E-409VT3 treated with Poncho 250/TrilexFL Maxim XL, seeded at 26,500 seeds/acre in 30 inch rows. The second site was embedded within a different experiment and consisted of a check, 50 lb additional N and 100 lb additional N.
There was an increase in yield from the check to the 40 lb N treatments and greater, but no difference from the 40 lb N rate to the higher treatments (Table 2). The total available N in the check at this site was 51 lb N from residual nitrate, 3 lb N from 10-34-0 with the planter, and 50 lb N/acre from long-term no-till for a total of 104 lb/acre known available N. With a yield of approximately 140 bu/acre, that would make the rate that maximized yield equal to about 1 lb N/bu, which is similar to the ratio at Rutland. The Greenseeker as used was not a good indicator of N status early in the season (Table 3). There were no differences in NDVI readings between treatments.

Table 2. Site 1 corn yield with 6 N treatments in Barnes County, 2010.

Treatment, lb N/acre	Yield, bu/acre	Test Weight, lb/bu
Check	111	55.9
40	133	56.1
80	144	56.4
120	131	56.2
160	142	56.2
200	145	56.4
F	7.92	0.44
P	0.001	0.81
LSD	13	NS

Table 3. NDVI at Site 1 in Barnes County

Treatment, lb N/acre	NDVI
Check	0.64
40	0.69
80	0.71
120	0.70
160	0.72
200	0.75
F	2.06
P	0.12
LSD	NS

At site 2, yields were maximized with the total available N rate of 153 lb/acre (Table 4). Test weight was not affected. The Greenseeker was not used at site 2.

Table 4. Yield with N rate at Barnes, site 2, 2010.

Treatment in terms of total known available N	Yield, bu/acre	Test Weight, lb/bu
Check, 103 lb/acre	85	55.3
153 lb/acre	125	55.7
203 lb/acre	123	56.0
F	9.0	0.3
P	0.0004	0.6
LSD 5%	20	NS

Walcott E, Richland County
This plot was located on soybean stubble southeast of Walcott, ND, about 3.5 miles south on County Road 1 from the Walcott Road at 46^o 29.7’ north latitude and 96^o 53’ west longitude. The soil was an Embden sandy loam (coarse-silty, loamy, mixed, superactive, frigid Pachic Hapludolls). The field has been historically In a conventional tilled system. The plot area was covered in the spring prior to tillage with a very thick stand of lambsquarter, which may have functioned as a cover crop. The residual nitrate was 24 lb/acre, P was 4 ppm, K was 135 ppm, OM was 2.1% and Zn was 2 ppm. Since the grower applied a mixed N fertilizer to the field, but not to the plot area, the plots were treated uniformly with 200 lb/acre 11-52-0 and 100 lb/acre 0-0-60 before the field was worked. The corn variety used was Pioneer Hi-bred 39N99, seeded on May 19 at 31,000 seeds/acre in 30 inch rows.

Table 5. NDVI, Walcott E, 2010 N rate trial.

Treatment	NDVI
Check	0.88
40	0.88
80	0.89
120	0.89
160	0.87
200	0.93
LSD 5%	NS

Table 6. Corn yield with N treatment, Walcott E, 2010 N rate trial.

Treatment, lb N/acre	Yield, bu/acre	Test Weight, lb/bu
Check	170	57.3
40	203	57.6
80	219	58.4
120	241	58.7
160	225	58.6
200	233	58.7
F	18.5	5.9
P	0.001	0.03
LSD	13	0.9

There were no differences in NDVI readings with treatment. There were significant increases in corn yield and test weight with N treatment. Check and 40 lb N/acre rates were lower in test weight than higher N rates. The highest yield was obtained with 120 lb N/acre, which is a total of 206 lb/acre of known available N (24 lb/acre residual N, 22 lb/acre fertilizer P, 40 lb/acre from soybean stubble).

Lidgerwood, Richland County
This field was located along Rt 18 N of Lidgerwood at about 46^o 10’ north latitude and 97^o 08’ west longitude. The field was in soybean in 2009, with the stubble remaining on the surface until it was worked in the spring just prior to planting. The field has been in conventional till historically. The soil was a Gardena loam (coarse silty, mixed, superactive, frigid Pachic Hapludolls). Residual nitrate was 35 lb N/acre, P was 5 ppm, K was 220 ppm, pH was 6.7, OM was 3.9%, and Zn was 1.8 ppm. Phosphate fertilizer was applied uniformly to the plot area at 100 lb 11-52-0 per acre. The field was in soybean stubble from 2009. Dekalb 4327 corn variety was seeded 4/28 at 29,000 seeds/acre in 30 inch rows. 3 gallon of 10-34-0 was applied in furrow as a starter. Total known available N was 35 lb residual N nitrate, 3 lb from starter and 40 lb soybeans = 78 lb/acre.

Table 7. NDVI, Lidgerwood, 2010 N rate trial.

Treatment	NDVI
Check	0.87
40	0.87
80	0.90
120	0.91
160	0.90
200	0.93
LSD 5%	NS

Table 8. Corn yield with N treatment, Lidgerwood, 2010 N rate trial.

Treatment, lb N/acre	Yield, bu/acre	Test Weight, lb/bu
Check	162	56.3
40	194	56.5
80	185	55.4
120	198	56.6
160	209	56.7
200	197	57.0
F	2.3	1.98
P	0.09	0.14
LSD	28 (10%)	NS

The N rate associated with the highest yield is not clear from Table 8. Graphing the response in Figure 2 and applying regression analysis gives us a polynomial equation seen in the figure. By taking the derivative of the equation and solving for x, the solution gives us the peak of the curve at 238 lb N/acre. Given that the highest yield was 209 bu/acre, this produces a formula of about 1.1 times achieved yield for optimal N rate, not considering economics.



Figure 2. Yield trend with N rate, Lidgerwood, 2010.

Christine, Richland County

This field was located about 3 miles west of the I29 Christine exit on Fargo silty clay soils (fine, smectitic, frigid Typic Epiaquerts). The field was previously in soybean. The plots were located well within the field to avoid possible early season flooding, which turned out to be a good plan. The residual soil nitrate was 42 lb/acre to a 2 foot depth, P was 15 ppm, OM was 4.7%, Zn was 1 ppm, K was 440 ppm. Phosphate at a rate of 100 lb 11-52-0 per acre was applied to the plots uniformly before the field was worked. The field worked up wet before planting and influenced final stands within the plot. Variety Pioneer P38M58 was seeded at 30,000 seeds/acre on April 28 in 22 inch rows. A row starter of 5 gal/acre 9-18-9 was applied.
Since there was variability in stand within the plots, the row with the highest population was noted and counts made. The stand count was used as a covariate in the final yield analysis for treatment differences. The noted row was the row harvested for yield.
There were no differences between treatments with Greenseeker NDVI readings (Table 9).

Table 9. NDVI, Christine, 2010 N rate trial.

Treatment	NDVI
Check	0.74
40	0.79
80	0.78
120	0.79
160	0.75
200	0.82
LSD 5%	NS

Table 8. Corn yield with N treatment, Lidgerwood, 2010 N rate trial.

Treatment, lb N/acre	Yield, bu/acre	Test Weight, lb/bu
Check	70	52.8
40	106	53.1
80	106	53.8
120	130	54.3
160	130	54.8
200	104	53.4
LSD	36	NS

Corn yield was increased with N, peaking at about 120 lb supplemental N. The total available N at this rate was 218 lb N/acre. This is about 1.6 lb N per achieved bushels which is similar to the ratio for the other heavy, wet soil in the study at Prosper South. If the real ratio of N to yield was similar to other conventional till eastern studies, this field lost about 75 lb N/acre through denitrification during the May-early June wet period.

Hankinson, Richland County

This site was located along Highway 11, about 4.5 miles west of Hankinson on Forman loams (fine-loamy, mixed, superactive, frigid Calcic Argiudolls). The field was in soybean in 2009 and tilled in the fall prior to freeze-up. The field has been in a conventional till system. The residual nitrate to 2 foot depth was 70 lb/acre, P was 10 ppm, K was 200 ppm, Zn was 2.2 ppm, OM was 4.3%, and pH was 7.9. P was applied uniformly to the plots as 100 lb/acre 11-52-0 on 4/16 prior to spring tillage along with fertilizer N treatments. Variety Dekalb 4327 was planted April 23 at 29,000 seeds/acre with 4.5 gal/acre 10-34-0 (about 5 lb N/acre). Total known available N for this site is 70 lb N from residual nitrate, 5 lb/acre for starter, 11 lb/acre as phosphate fertilizer and 40 lb/acre for soybean previous crop, totaling 126 lb N/acre. The plots were harvested September 14.

Table 9. Greenseeker NDVI, Hankinson, 2010 N rate trial.

Treatment	NDVI
Check	0.78
40	0.83
80	0.84
120	0.91
160	0.84
200	0.90
LSD 5%	NS

There were no differences in Greenseeker NDVI readings with N rate (Table 9). N application increased yield, but not test weight (Table 10). The regression analysis of the relationship between total known available N to corn yield suggests that corn yield may not have peaked with 326 lb N/acre (Figure 3). This suggests that some N losses through a combination of leaching and denitrification probably occurred early in the season.

Table 10. Corn yield with N treatment, Hankinson, 2010 N rate trial.

Treatment, lb N/acre	Yield, bu/acre	Test Weight, lb/bu
Check	158	56.8
40	178	56.3
80	180	56.6
120	200	57.0
160	201	56.8
200	213	57.0
LSD 5%	32	NS

Figure 3. Relationship of total available N to corn yield, Hankinson, 2010.

Embden, Cass county
This site was located about 2 miles southwest of the Embden exit of I-94. The soil was a Gardena loam (coarse-silty, mixed Pachic Udic Hapludolls). The previous crop was spring wheat. The residual nitrate to 2 foot depth was 42 lb/acre, P was 14 ppm, K was 180 ppm, OM 2.7%, pH was 7.4, and Zn was 0.6. Corn varieties Garst 89K64GT and Pioneer 8581R were planted April 27 at a population of 29,600 seeds/acre in 30 inch rows. 100 lb/acre of 11-52-0 was applied to the plot prior to spring tillage. The field has been conventionally tilled historically. The plots were harvested September 8.

Table 11. NDVI, Embden, 2010 N rate trial.

Treatment	NDVI
Check	0.85
40	0.85
80	0.87
120	0.93
160	0.87
200	0.89
LSD 5%	NS

Table 12. Corn yield with N treatment, Embden, 2010 N rate trial.

Treatment, lb N/acre	Yield, bu/acre	Test Weight, lb/bu
Check	166	56.1
40	178	56.9
80	166	56.1
120	165	57.1
160	196	56.4
200	199	56.9
F	2.0	4.0
P	0.14	0.02
LSD	33	0.8

There were no treatment differences in Greenseeker NDVI readings (Table 11). Test weight was maximized at 40 and 120 lb N/acre rates, but the trends were not consistent with N rate (Table 12). Corn yield was maximized with the 200 lb N rate. The total known available N at this rate was 242 lb/acre, or about 1.2 times achieved bushels/acre.

Prosper West, Cass county
This site was located about 1 mile west of the NDSU Prosper Research Station along the Amenia road. The soils were Bearden silt loams (fine-silty, frigid Aeric Calciaquolls). The field was in dry bean the previous year and the farm has been historically conventional till. Residual nitrate was 31 lb in the 2 foot depth. P was 24 ppm, K was 150 ppm, OM was 3%, Zn was 1.9 ppm.
Corn variety ProSeed 990GPCBLL was planted April 25 at 32,800 seeds/acre in 20 inch rows. Harvest stand was 28,100 plants/acre. Row starter was used at 4 gal/acre 10-34-0 (about 5 lb N/acre). Ears were harvested September 20. Total Known Available N was 31 lb residual N, 5 lb from starter and 40 lb from dry beans to a total of 76 lb N/acre.

Table 13. NDVI, Lidgerwood, 2010 N rate trial.

Treatment	NDVI
Check	0.81
40	0.69
80	0.76
120	0.78
160	0.77
200	0.77
LSD 5%	NS

There were no treatment differences in Greenseeker readings with N rate (Table 13). Corn test weight was not affected by N rate. Corn yield was maximized at 120 lb supplemental N, or 196 lb/acre total known available N. This is about 0.9 times achieved yield. The other corn plot that followed dry edible bean also had a relatively high efficiency N rate (Dwight).

Table 14. Corn yield with N treatment, Lidgerwood, 2010 N rate trial.

Treatment, lb N/acre	Yield, bu/acre	Test Weight, lb/bu
Check	179	55.1
40	181	56.5
80	190	55.5
120	219	55.0
160	217	55.2
200	217	54.5
F	3.0
P	0.05
LSD	15	NS

Arthur, Cass county
This site was located about 4 miles Northwest of Arthur, ND. The soils are Galchutt fine sandy loams (fine, smectitic, frigid Vertic Argialbolls). The previous crop was soybean and the field has been historically conventional till. Residual nitrate was 42 lb/acre to 2 foot depth, P was 10 ppm, K was 160 ppm, OM was 2.6%, and Zn was 0.8 ppm. P was uniformly applied to the plot at a rate of 100 lb/acre 11-52-0 directly after seeding. N treatments were applied prior to spring tillage. Variety 2P174 was planted April 23 at 33,000 seeds/acre in 20 inch rows with 3 gal 10-34-0 per acre as a row starter (about 4 lb N/acre). Harvest stand was about 28,100 plants/acre. Corn ears were harvested September 20. Total Known Available N was 42 lb residual N, 4 lb from starter, 11 lb from P, and 40 lb from bean stubble, for a total of 97 lb known available N.

Table 15. NDVI, Arthur, 2010 N rate trial.

Treatment	NDVI
Check	0.79
40	0.80
80	0.85
120	0.80
160	0.84
200	0.84
LSD 5%	NS

Table 16. Corn yield with N treatment, Arthur, 2010 N rate trial.

Treatment, lb N/acre	Yield, bu/acre	Test Weight, lb/bu
Check	162	56.8
40	178	57.9
80	196	58.3
120	202	57.6
160	208	58.0
200	228	58.0
F	6.9	1.90
P	0.02	0.14
LSD	26	NS

There were no Greenseeker reading differences due to N rate treatments (Table 15). There were no test weight differences due to treatments, but N rates increased yield. Maximum yields were achieved at an N rate of 200 lb/acre, or a total available N rate of 297 lb/acre (Table 16). The 1.3 times achieved yield was the least efficient non-heavier soil site. Perhaps 20-40 lb N may have leached from these soils during the May wet period.

Walcott west, Richland county
This site was located about 12 miles southwest of Walcott, ND on Embden sandy loams (coarse-loamy, mixed, superactive, frigid Pachic Hapludolls). The field has historically been conventional till and the previous crop was soybean stubble. Field had been chiseled in the fall. Residual nitrate to a 2 foot depth was 42 lb/acre. P was 7 ppm, K was 100 ppm, OM was 3.2%, and Zn was 1.3 ppm. P and K were uniformly and separately applied to the plots prior to the second spring tillage prior to seeding using 200 lb/acre 11-52-0 and 100 lb/acre 0-0-60. There was no row starter applied. Dekalb 4327 was seeded at 32,000 seeds/acre on April 27 in 30 inch rows. Total known available N was 42 lb residual, 40 for soybean stubble, and 22 for P fertilizer for a total of 108 lb N/acre.

Table 17. NDVI, Walcott West, 2010 N rate trial.

Treatment	NDVI
Check	0.86
40	0.88
80	0.91
120	0.90
160	0.91
200	0.90
LSD 5%	NS

Table 18. Corn yield with N treatment, Walcott West, 2010 N rate trial.

Treatment, lb N/acre	Yield, bu/acre	Test Weight, lb/bu
Check	158	56.1
40	201	57.0
80	181	56.9
120	203	57.1
160	207	56.7
200	214	57.0
F	3.9	1.04
P	0.02	0.4
LSD	11	NS

There were no Greenseeker NDVI differences due to treatment (Table 17). Test weight was not affected by treatment (Table 18). Grain yield was increased with N rate up to 120 lb supplemental N/acre or 228 lb total known available N. The optimal N rate results in a formula of about 1.1 lb N per achieved bushel.

Page, Cass county
This site was located on the Gardner road about 6.5 miles west of the Highway 18 intersection. The soil survey maps the area as Barnes loams, but the soil cores looked more like Embdens (coarse-loamy, mixed, superactive, frigid Pachic Hapludolls). The field had previously been in corn and the residue was burned early in spring 2010 before the study commenced. Very little stubble remained. N treatments were applied 4/15 and the crop was seeded 4/23. There was very poor emergence, so the field was worked again and replanted 5/29. Residual nitrate was 28 lb N/acre. The grower applied P and K to the plot area along with the field, but no nitrogen. The harvest stand was about 27,300 plants/acre in 20 inch rows. Ears were harvested September 30.

Table 19. NDVI, Page, 2010 N rate trial.

Treatment	NDVI
Check	0.47
40	0.50
80	0.52
120	0.52
160	0.54
200	0.52
LSD 5%	0.04

Table 20. Corn yield with N treatment, Page, 2010 N rate trial.

Treatment, lb N/acre	Yield, bu/acre	Test Weight, lb/bu
Check	129	53.6
40	148	53.5
80	166	53.7
120	158	54.1
160	162	53.6
200	165	54.1
F	7.2	0.21
P	0.001	0.95
LSD	9	NS

There was an increase in Greenseeker NDVI readings with N rate to about 80 lb supplemental N (Table 19). This field was sensed earlier in the season (about 2 feet tall) compared to later in the growing season (about 3-3.5 feet tall) for most other sites. Earlier reading appears to be essential to a better relationship of N status with Greenseeker readings; at least those taken above the canopy.
Corn grain yield was increased with N rate to about 80 lb N/acre (Table 20). Total known available N is 28 lb/acre residual nitrate. The grower P addition added at least 11 lb N/acre for a total of 39 lb N/acre. Total N applied and know was about 119 lb N/acre for a yield of about 165 bu/acre. This seems more efficient than reasonable. Since the corn residue was burned off, one would expect there to be substantially less N tie-up by residue and the field should act more like it would if it were bean stubble the year before. If we add a 40 lb N credit for no residue, or total N required to achieve 165 bu/acre becomes 159 lb/acre, which is reasonable compared with other conventional medium or lighter texture soil sites.

Wheatland, Cass county
This site was located about 3.5 miles west of the Wheatland road curve on Wyndmere sandy loams (coarse-loamy, mixed, superactive, frigid Aeric Calciaquolls). The field was in soybean stubble the previous year and the field has been historically conventional till. Residual nitrate was 24 lb N/acre, P was 3 ppm, K was 90 ppm, pH was 7.7, OM was 1.6%, Zn was 0.7 ppm. The grower had 160 lb/acre 11-52-0 and 210 lb/acre 0-0-60 applied to the field and plot area before spring tillage. Starter of 3 gal/acre of 10-34-0 was applied at planting, or about 4 lb N/acre. Total known available N was 24 lb residual nitrate, 18 lb/acre with P fertilizer , 4 lb/acre with starter and 40 lb/acre with bean stubble for a total of 86 lb N/acre. NK8977 corn variety was planted April 24 at a seeding rate of 32,000 seeds/acre in 22 inch rows. Harvest stand was about 26,400 plants/acre.

Table 21. NDVI, Wheatland, 2010 N rate trial.

Treatment	NDVI
Check	0.72
40	0.81
80	0.79
120	0.84
160	0.83
200	0.86
LSD 10%	0.08

Table 22. Corn yield with N treatment, Wheatland, 2010 N rate trial.

Treatment, lb N/acre	Yield, bu/acre	Test Weight, lb/bu
Check	112	56.5
40	137	56.8
80	162	56.9
120	184	56.4
160	186	57.1
200	180	56.9
F	26.7	0.68
LSD	17	NS

Greenseeker NDVI increased from the check to the 40 lb/acre supplemental N rate (Table 21). Corn
Grain yield increased up to the 120 lb/acre N rate, or a total of 206 lb N for a yield of about 185 bu/acre, or about 1.1 times achieved bushels.

Dwight, Richland county
This site was located about 1.5 southeast of the I-29 Dwight exit on Gardena loams (coarse-silty, mixed Pachic Udic Hapludolls). The field had previously been in dry edible bean in 2009. Residual nitrate to 2 foot depth was 73 lb/acre, P was 2 ppm, K was 90 ppm, pH was 8.2, Zn was 0.4, OM was 1.3%. P and K were uniformly and separately applied to the plot area at a rate of 200 lb/acre 11-52-0 and 100 lb/acre 0-0-60. Starter fertilizer was applied at planting by the grower at 5 gal/acre 6-24-6. Total known available N was 73 lb N from residual N, 22 lb/acre from 11-52-0, 3 lb/acre from 6-24-6 and 40 lb/acre from dry bean previous year for a total of 138 lb N/acre. Corn variety Pioneer 38A57 was planted at 33,000 seeds/acre on 5/19 in 30 inch rows.

Table 23. Greenseeker NDVI, Dwight, 2010 N rate trial.

Treatment	NDVI
Check	0.88
40	0.89
80	0.88
120	0.83
160	0.88
200	0.84
LSD 5%	NS

Table 24. Corn yield with N treatment, Dwight, 2010 N rate trial.

Treatment, lb N/acre	Yield, bu/acre	Test Weight, lb/bu
Check	183	59.1
40	206	59.1
80	198	60.1
120	206	59.2
160	213	60.3
200	210	59.9
F	33	1.26
P	0.03	0.33
LSD	18	NS

There were no Greenseeker NDVI differences with treatment (Table 23). Corn yield increased from the check to the 40 lb N rate, or a total known available N rate of 178 lb N/acre. This provides a formula of about 0.9 X achieved bushels/acre, similar to that of the Prosper west site which was also in dry bean the previous year. Perhaps the current credit for dry bean stubble is too low.

Prosper south, Cass county
This site was located about 1.5 miles southwest of Prosper on Bearden silty clay loams (fine-loamy, mixed, superactive, frigid Aeric Calciaquolls). Residual nitrate to 2 foot depth was 81 lb/acre. P was 21 ppm, K was 400 ppm, pH was 7.4, OM was 4.2% and Zn was 0.9 ppm. This site was originally seeded April 23, but emergence was poor, and the site was overseeded with Peterson Farm Seed variety 24M83RR at 36,000 seeds/acre in 22 inch rows. The original plants that survived the first planting were removed by hand-hoeing. The original planting received 5 gal/acre 10-34-0, or about 6 lb N/acre. The field was previously in soybean and the field has been historically conventional till. Total known residual N was 81 lb residual, 6 lb from starter and 40 from previous soybean for a total of 127 lb/acre.

Table 25. Greenseeker NDVI, Prosper South, 2010 N rate trial.

Treatment	NDVI
Check	0.67
40	0.71
80	0.72
120	0.75
160	0.74
200	0.74
LSD 5%	NS

There were no differences in Greenseeker NDVI due to treatment (Table 25).

Table 26. Corn yield with N treatment, Prosper South, 2010 N rate trial.

Treatment, lb N/acre	Yield, bu/acre	Test Weight, lb/bu
Check	125	55.3
40	145	56.0
80	154	55.6
120	158	56.5
160	184	57.2
200	179	56.4
F	1.81	1.8
P	0.11	0.18
LSD 5%	40	NS

Using LS means instead of an LSD, there was an increase in yield from the check (127 lb/acre total known available N) to the 40 lb rate (167 lb/acre total known available N).


Figure 4. Relationship between total known available N and corn yield at Prosper South, 2010.

Using regression analysis, the N rate that would maximize un realized yield of 199 bu/acre would be about 473 lb N/acre. If we are more conservative and accept 184 bu/acre as our highest achievable yield, it took 160 lb/acre added N plus the 127 lb total known available N or 287 total known available N to achieve 184 bu/acre. This is a formula of about 1.6 times achievable yield. To have the formula read 1.2 times achievable yield accepts that about 80 lb N/acre were lost to denitrification during the wet May period.

Amenia, Cass county
This site was located about 3.5 miles northwest of Amenia. There is no published soil survey of the field, but the soil cores looked like a Bearden silt loam (fine-loamy, mixed, superactive, frigid Aeric Calciaquolls). The field was previously in soybean and had a history of conventional tillage. Residual nitrate to a 2 foot depth was 40 lb/acre, P was 11 ppm, K was 140 ppm, pH was 6.3, OM was 2.4% and Zn was 0.4 ppm. Corn variety Pioneer Hi-Bred 39V07 was planted at a 34,500 seed/acre rate on April 28 in 22 inch rows. Plots were harvested September 3. Harvest stand was 32,940 plants/acre. Total known available N was 40 lb/acre residual N and 40 lb from previous soybean for a total of 80 lb N/acre.

Table 27. Greenseeker NDVI, Amenia, 2010 N rate trial.

Treatment	NDVI
Check	0.83
40	0.87
80	0.89
120	0.87
160	0.89
200	0.89
LSD 5%	NS

Table 28. Corn yield with N treatment, Amenia, 2010 N rate trial.

Treatment, lb N/acre	Yield, bu/acre	Test Weight, lb/bu
Check	162	55.9
40	194	56.1
80	181	56.4
120	197	56.2
160	200	56.2
200	192	56.4
F	4.0	0.44
LSD 5%	35	NS

There were no differences in Greenseeker readings with N rate (Table 27). Yield increased with N rate to about 120 lb N/acre, or 200 lb total known available N/acre. This would make the N formula to achieve maximum yield about 1 times achieved yield.

Carrington, dryland, Foster county

This study was conducted by Greg Endres and Paul Hendrickson at the Carrington R & E center under dryland (non-irrigated) conditions on Fram-Wyard loams (Coarse-loamy, mixed, superactive, frigid Aeric Calciaquolls and Typic Endoaquolls). Variety Dekalb 33-53 was seeded 5/4 at 26,000 seeds/acre into worked wheat stubble in a conventional tilled system in 30 inch rows. Starter fertilizer at a rate of 5 gal/acre 10-34-0 was used at planting. Residual nitrate to 2 foot depth was 37 lb/acre, P was 7 ppm, K was 148 ppm, OM was 3.7%, Zn was 0.6 ppm. Total known available N at planting was 43 lb/acre. The Greenseeker was not used at the Carrington sites. Corn ears were harvested 10/13. There were no significant yield effects of N at this site. Regression analysis showed that the maximum yield of about 163 bu/acre was achieved with 120 lb supplemental N, or about 163 lb/acre total known available N, or about 1 times yield achieved.

Table 29. Corn yield with N treatment, Carrington dryland, 2010 N rate trial.

Treatment, lb N/acre	Yield, bu/acre	Test Weight, lb/bu
Check	142	56.6
40	148	56.0
80	157	56.5
120	163	56.9
160	168	56.5
200	168	57.0
LSD 5%	NS	NS

Carrington irrigated, Foster county
This study was conducted on the Carrington R&E Center under irrigation on Heimdal-Emrick loams (coarse-loamy, mixed, superactive, frigid Calcic Hapludolls and Pachic Hapludolls). The previous crop was sunflower and the field has been under continuous conventional tillage. Residual N was 27 lb/acre, P was 11 ppm, K was 172 ppm, Zn was 1.1 ppm, pH was 7.9 and OM was 3 %. 5 gallon of 10-34-0 (6 lb N) was applied as a row starter at planting. Corn variety DK33-53 was planted at a 30,000 seeds/acre planting rate in 30 inch rows on 5/4. Harvest was on 10/13. Total known residual N was 33 lb/acre.

Table 30. Corn yield with N treatment, Carrington, irrigated, 2010 N rate trial.

Treatment, lb N/acre	Yield, bu/acre	Test Weight, lb/bu
Check	140	55.6
40	150	55.8
80	159	56.3
120	176	55.9
160	165	56.1
200	166	55.7
LSD 5%	22	NS

Yield was increased by N rate to the 120 lb/acre supplemental N rate or 153 lb N/acre to achieve about 176 bu/acre. This is about 0.9 lb N per achievable bushels/acre.

Golden Valley county
This study was conducted by Roger Ashley out of the Dickinson R & E Center. Residual nitrate was 46 lb/acre to 2 foot depth. P was 11 ppm, K was 460 ppm, pH 7.8, OM 3.8%, Zn 0.2 ppm. Other details of the study are not available at this time.

Table 31. Corn yield with N treatment, Golden Valley county, 2010 N rate trial.

Treatment, lb N/acre	Yield, bu/acre
Check	77
40	87
80	91
120	94
160	92
200	102
F
LSD 5%	9.7

The maximum yield achieved was 102 lb N/acre with a total available N rate, including supplemental N of 243 lb N/acre (Table 31). A similar statistical yield of 94 bu/acre was achieved with 163 lb N/acre. The economics of achieving a 3 bu/acre response going from supplemental N of 80 to `120 lb N/acre is questionable. The economic rate of total N was probably around 123 lb total available N/acre.

Grant county, New Leipzig
This study was also conducted by Roger Ashley out of the Dickinson R & E Center. Residual nitrate to 2 foot depth was 38 lb/acre. P was 23 ppm, K was 480 ppm, pH was 5.4, Zn was 1.2 ppm, OM was 4.9%.

Table 32. Corn yield with N treatment, Grant county, New Leipzig, 2010 N rate trial.

Treatment, lb N/acre	Yield, bu/acre
Check	84
40	93
80	90
120	94
160	102
200	93
LSD 5%	10

Corn yield increased with N treatments. The highest yield of 102 bu/acre was achieved with a total known available N including applied N of 198 lb/acre.

Summary of entire study together, then separated-

With all of the yield vs total known available N, there is a reasonable upward relationship (Figure 5). However, the relationship improves as similar studies are combined and taken out of the entire database and considered separately. The relationship west-river is provided in Figure 6, with an r² of over 0.6 compared to about 0.2 in Figure 5.

Figure 5. Corn yield with N rate, all 20 experiments, 2010.



Figure 6. Corn yield with total known available N for west-river sites only.



Figure 7. Application of the Return to N model to west-river sites.

The rate of N providing maximum return west-river at $3/bushel corn and 40 cent N is 63; at $4 corn, the rate becomes 118 lb/acre; at $5 corn it is 153 lb/acre and at $6 corn it is 174 lb/acre. At 60 cent N, the rate at $3/bushel corn is 0; at $4 corn 35 lb/acre, at $5 corn 83 and at $6 corn 117 (Figure 7). The importance of corn price dominates the analysis. N cost is of some consideration, but does not change profitability or influence rate as much as corn price.



Figure 8. Eastern ND data (without west-river) total known available N vs corn yield, 2010 plots.
When the west-river data is removed from the data set (Figure 8), the relationship in eastern sites is improved.


Figure 9. Eastern sites without the heavy clay sites, 2010.


Figure 10. Eastern non-heavy clay sites, 2010 return to N analysis.

Analysis of Eastern sites without the Prosper South and Christine heavy clay sites provides a better relationship (Figure 9). Analysis of return to N shows that $3 corn rates should be from 200-250 lb total known available N, whereas with $5 corn, the rates range from 250-300 lb/acre total known available N (Figure 10).

Figure 11. Eastern clay sites only, 2010.


Figure 12. Eastern clay sites only, 2010, return to N analysis.

Combining the data from the heavy clay sites, Prosper South and Christine show that possible yield is probably not realized at these sites due to N losses in the season (Figure 11). The return to N analysis shows that rates on these sites should have been higher than 300 lb/acre total known available N for profits to peak (Figure 12). Of course, if losses had not occurred, yield potentials would have been reached at rates far less than this. These data suggest that perhaps these fields might benefit from application timing that delays N application until after early spring wetness, such as sidedress.

Figure 13. Eastern no-till sites, 2010.


Figure 14. Eastern no-till sites, return to N analysis using 50 lb N long-term no-till credit.


I think that the graph of relationship of total known available N in Figure 13 is misleading. The total N rates that peaked yield in the individual analysis were around 150 lb total available N/acre. The total available N calculated for these sites also incorporated the long-term no-till 50 lb N/acre credit established during the spring wheat and durum N recommendation review in 2009. If this credit was not worked into the total known available N formula, the eastern no-till sites would peak about 50 lb N/acre less N than their conventional tillage study counterparts (Figure 14).

Summary-
A new recommendation of N for corn cannot and should not be produced just from the 2010 data. Two more years and about 40 more site years of ND data should be generated before a new recommendation system is attempted. There are some consistencies, however, between this corn data set and the spring wheat and durum data sets from 2005-2009. There is a need to incorporate the long-term no-till credit into the corn recommendations. Different parts of the state (east and west) should be considered separately. Within a region, textural differences between soils may need to be considered.