Nitrogen Application to Irrigated Soybean during Early Reproductive Growth

Impact on Soybean Production and Value

Currently, we have inconsistent evidence for a high probability of yield increases due to soil application of N at R3 if yields are above 60 bu/Ac and strong evidence of no advantage for lower yield situations. This study will help growers make an informed decision as to whether to apply nitrogen to soybeans or not.

Charles Wortmann (2010)

Key Terminology

R3 growth stage is beginning pod fill

Study Objectives

The objectives of this research were to determine for high yield (>60 bu/ac) soybean in eastern and south central Nebraska the probability of response to soil application of N at R3 for high yield soybean and the conditions where response is most likely to occur, and to develop a practical framework for N management in high yield soybean in Nebraska.

Findings

Yield increases due to application of N at R3 were small. Assuming a fertigation cost of 10% of the purchase price of urea ammonium nitrate, the results indicated that N application at R3 is on average profitable when the price ratio of soybean ($/bu) to N ($/lb) is > 12 in south central Nebraska and > 19 in northeast Nebraska. There was no indication of profitability in southeast Nebraska. Recovery of applied N in the grain was 30 and 19% for south central and northeast Nebraska sites, respectively.

The results of this study indicate a probability of about 60% of increasing soybean yield by >1.5 bu/ac with application of 27 lb/ac N at R3 for soybean of >60 bu/ac yield, but only 32% for southeast Nebraska. Depending on the price of N relative to the expected soybean price, N application to soybean at R3 is likely to be profitable for fields in south central or northeast Nebraska that are equipped for fertigation. Soil and leaf tissue analysis results were not related to response and are not likely to be useful in predicting response.

Area

Trials

0 N&S

27N

54 N

27N,5S

Diff†

P†

 

 

Yield, bu/ac

 

All trials included

Northeast

20

64.9

66.4

66.7

65.8

1.5

0.02

Southeast

30

68.6

68.3

68.2

68.2

-0.3

0.36

South central

6

67.8

70.6

70.4

66.8

2.8

0.06

Trials with >60 bu/ac yield

Northeast

17

69.5

71.1

71.1

70.4

1.6

0.01

Southeast

22

72.3

72.6

72.6

72.6

0.3

0.64

South central

5

69.6

72.1

73.5

70.4

2.5

0.00

†The difference in yield for 27 lb/ac N applied compared with no N applied.