Conclusions• Fall application of urea and ammonium

sulfate produced lower corn yield and greater nitrate losses than when spring-applied.

• Averaged across N rates, fall application of ammonium sulfate increased nitrate loss by 36% (8 lb/A) while reducing net return to fertilizer by 16% ($23/A).

Developing Nitrogen BMPs from Field ResearchGyles W. Randall* and Jeffrey A. Vetsch, Univ. of Minnesota, Waseca, MN

AbstractBest management practices (BMPs) for nitrogen (N) and their implementation are critical to achieving profitable crop production while minimizing nitrate losses to ground and surface waters. Nitrogen BMPs for corn (Zea mays) grown after soybean (Glycine max) in south-central Minnesota were developed from long-term, subsurface tile drainage research conducted at the University of Minnesota’s Southern Research and Outreach Center at Waseca. A four-year study showed significantly greater nitrate losses in tile drainage accompanied by no increase in corn yield or profitability when applied N rates exceed the University’s recommended rate. A 15-year study indicated that spring application of ammonia produced greatest yield and profit while minimizing nitrate loss to drainage compared with fall-applied ammonia without N-Serve, and thus is a preferred BMP. Fall application of ammonia with N-Serve also significantly reduced nitrate losses but is considered a BMP with RISK because yields and economic return were lower in years when May and/or June were very wet. Results from these studies clearly show application rates in excess of University recommendations and fall application of ammonia without N-Serve are not BMPs for south-central Minnesota.

Experimental Procedures

Soil: Canisteo clay loam, Typic Endoaquoll

Years: 1987 – 2003

Tile plots: 36; 16 corn, 16 soybean and 4 grass

Plot size: 30 ft. by 20 ft. simulating 50 ft. tile spacing. Isolated to a depth of 6 ft. by 12 mil plastic sheeting.

Tile depth: 3.5 ft.

Slope: 0 – 1 %

Tile drainage research facility at Waseca.

Schematic diagram of drainage plot details.

20’

30’

5’

Collection sump

Rate and Time of Application

Nitrogen Source and Time of Application

Time of N Application and Nitrification Inhibitors

Region Specific BMPs for N

Date

10

15

20

25

30

35

40

Nitr

ate

Co

nc

(mg

/L)

80 lb N/A 120 160

Effect of N rate for corn after soybean on NO3-N concentration in tile drainage water in 2001.

Purpose

• To determine the effect of N rate, time of application, and nitrapyrin (N-Serve) on nitrate losses to subsurface, tile drainage and on corn production.

• To develop best management practices (BMPs) for N for south-central Minnesota based on long-term field research.

Proposed BMPs for South-Central Minnesota

• Recommended– Spring preplant applications of ammonia or

urea and split applications of ammonia, urea, or UAN are highly recommended.

• Incorporate broadcast urea or UAN within three days.

• Apply sidedress application before corn is 12 inches tall.

• Inject or incorporate sidedress applications of urea or UAN to a minimum depth of 3 inches.

• Recommened, but with greater risk– Fall application of AA+N-Serve after soil

temperature at 6-inch depth is below 50° F.– Single, spring preplant application of UAN.– Side dressing all N before corn is 12 inches

tall.• Not recommended

– Fall application of urea, ammonium sulfate, UAN, or anhydrous ammonia without N-Serve.

References

Randall, G.W., and D.J. Mulla. 2001. Nitrate-N in surface waters as influenced by climatic conditions and agricultural practices. J. Environ. Qual. 30:337-344.

Randall, G.W., and J.A. Vetsch, and J.R. Huffman. 2003. Nitrate losses in subsurface drainage from a corn-soybean rotation as affected by time of nitrogen application and use of nitrapyrin. J. Environ. Qual. 32:1764-1772.

Randall, G.W., J.A. Vetsch, and J.R. Huffman. 2003. Corn production on a subsurface-drained Mollisol as affected by time of nitrogen application and nitrapyrin. Agron. J. 95:1213-1219.

Randall, G.W., and J.A. Vetsch. 2005 Nitrate losses in subsurface drainage from a corn-soybean rotation as affected by fall vs. spring application of nitrogen and nitrapyrin. J. Environ. Qual. 34(2):590-597.

Randall, G.W., and J.A. Vetsch. 2005. Corn production on a subsurface-drained Mollisol as affected by fall versus spring application of nitrogen and nitrapyrin. Agron. J. 97:472-478.

Acknowledgement

Sincere appreciation is extended to Dow AgroSciences for their financial contribution to this research.

Conclusions

• Applying 120 lb N/A in the spring (a BMP) increased corn yield 5% and reduced nitrate losses in drainage water by 27% compared to a fall application of 160 lb N/A.

• Reducing the N rate from 120 lb/A to 80 lb/A reduced yield by 17% and nitrate loss by 13%.

• Forty-six percent of the nitrate lost in tile drainage from a corn-soybean rotation was lost in the year soybeans were grown.

Effect of N rate and time of application on nitrate-N losses to subsurface

drainage and continuous corn yield.

14316034Fall180168

150131

66bu/AYield

5-Yr Average

26

1927

7lb N/A/yr

in drainageof nitrate

Annual loss

154Spring180

135Spring120100Fall120- -- -0$/Alb/A

Net returnTimeRateN treatment *

* Ammonium sulfate applied to continuous corn about Nov. 1 or May 1.

Corn yield and N recovery in the whole plant as influenced by time of application

and N source, 1997-99.

63170Yes““60168NoAmmonia“47158Yes““

8112182185

152bu/AYield

3-Yr Average

- -- -None- -84NoAmmonia“

LSD (0.10):

76NoUreaSpr. PP

43NoUreaFall%

N RecoveryN-ServeSourceTimeN Management

Effect of time of N application and N-Serve on corn yields after soybean, 1987–2001.

12.012.214.115-Yr Avg. FW NO3-N Conc. (mg/L)

* Corn = $2.00/bu; N = $0.25/lb N (fall) & $0.275/lb (spring).

** Seven years when statistically significant differences occurred.

$51.00$22.50---7-Yr Avg. Economic return over fall N ($/A/yr) *

1581461317-Yr Avg. Yield (bu/A) **

$18.80$9.30---15-Yr Avg. Economic return over fall N ($/A/yr) *

15615314415-Yr Avg. Yield (bu/A)

SpringFall+N-ServeFallParameter

Time of N Application

Corn production and nitrate loss as affected by time of N application and N-Serve, 1987-93.

14.656145NoSplit

13.747139NoSpring

4LSD (0.10):

13.743139Yes“

16.834131NoFall

- mg/L -$/Abu/A

Drainage *return to NyieldN-ServeTime

conc. in tileEconomicCornN treatment

FW NO3-N7-Yr Average

* Across the 4-cycle corn (1990-93) – soybean (1991-94) rotation.

Conclusions• Compared to late fall N application without

N-Serve over the 15-year period:– Corn yields were increased 9 and 12 bu/A/yr (6

and 8%) by either fall N+N-Serve or spring preplant N, respectively.

– Nitrate losses were decreased 14 and 15% by either fall N+N-Serve or spring preplant N, respectively.

• Spring-applied N-Serve did not improve water quality.

• No consistent evidence showing split or sidedress application to be superior from a water quality perspective.

Effect of N rate on yield of corn after soybean, net return to fertilizer N, and nitrate-N

concentration in tile drainage, 2000–2003.4-Yr FWNet4-Yr YieldN Treatment

120

160

120

80

0

lb/A

Rate

Spr.

“

“

Fall

---

Time

No

“

“

Yes

---

N-Serve

14105180

1878172

1370166

1230144

------111

mg/L$/A/Yrbu/A

NO3-N conc.ReturnAvg.