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Phosphorus Fertilizer Correlation to Kansas Soybeans
Robert Florence and Dave Mengel Kansas State Soil Testing Lab
What is a fertilizer correlation?
• Compare yields of non-fertilized areas to fertilized areas • across a range of soil nutrient levels – low to high • measured by a nutrient extractor – Bray, Mehlich... • Relative yields are used to compare across environments
• “Critical level”
• Where a non-fertilized yield almost equals a fertilized yield
Relative Yield % = Yield of plot with no fertilizer
Maximum yield from fertilized plot x 100
Fertilizer Correlation Graph (Ideal)
Soil test (ppm)
Re
lati
ve Y
ield
%
No
n f
ert
ilize
d p
lot
100
50
0
Deficient Sufficient
North Central Soybean Critical Levels
Source Term used Mehlich-3 or Bray-P1 Soil depth
ppm Inches
Kansas State Univ. Critical Level 20 6
North Dakota State Univ. Critical Level 15 6
South Dakota State Univ. Critical Level 15 6
Nebraska Univ. Critical Level 12 8
Iowa State Univ. Optimum 16-20 6
Michigan State Univ. Maintenance Fertilizer 15-30 8
NCERA-13
Our Goals
1) Review past P fertilizer applications on soybeans. 2) Conduct a current study evaluating soybean response to P fertilizer. 3) Examine if starter P fertilizer enhances yield above broadcast alone.
Past Data
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30 35 40 45
Re
lati
ve Y
ield
Pe
rce
nt
Bray P1 or Mehlich 3 P (ppm)
< 30 bu/acre average
> 30 bu/acre average
Kansas Fertilizer Reports – Agronomy Dept. from 1966 to 1988
Current Trials
2012 2013 2011
2
2
2
Sites
2011 2012 and 2013
Lbs P2O5 / acre
0 0
20 20
40 40
60 60
80 80
100
P broadcast as MAP (11-52-0)
Treatments
4 replications per site
Measured
Soils samples before fertilizer
Harvest
15’ (6-30” Rows)
Set up
Weighed on site
Broadcast Results
------------------- P2O5 lbs / acre ---------------
Location Mehlich 3 P 0 20 40 60 80 100 Probability
County ppm -------------------- Yield bu / acre ---------------
Woodson - 2011 5 32 B† 38 A 37 A 37 A 37 A -- 0.07
Lyon 8 17 17 18 17 19 18 0.57
Douglas 11 43 43 41 43 46 45 0.90
Atchison 11 48 B 41 C 50 B 48 B* 53 AB 58 A 0.00
Woodson - upland 16 32 36 37 34 33 34 0.42
Woodson - lowland 16 60 61 61 61 60 61 0.76
Cherokee - 2011 16 28 26 28 29 29 -- 0.66
Riley - Manhattan 21 53 51 54 53 51 56 0.65
Riley - Randolph 23 56 59 57 59 58 62 0.32
* Plot 203 removed
Correlation
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30 35 40
Re
lati
ve Y
ield
Pe
rce
nt
Mehlich 3 P (ppm)
2011
2013
Treatment Broadcast MAP
Starter APP
Total
---------------- P2O5 lbs/ac ----------------
1 20 0 20
2 0 20 20
3 40 0 40
4 20 20 40 5 60 0 60
6 40 20 60 7 80 0 80 8 60 20 80 9 100 0 100
10 80 20 100
Broadcast alone vs starter
Split Results
60
65
70
75
80
85
90
95
20 40 60 80 100
Re
lati
ve Y
ield
lbs P2O5 / acre
Broadcast Alone with Starter
Across All 2013 sites except Lyon Co.
Summary Correlation Data
Broadcast vs with starter
No response was seen above 16 ppm in 2013 The critical level could be between 15 and 20 ppm P
No difference was observed when similar amounts of P were applied
Remember phosphorus removal
0.8 lb P2O5 / bushel
Thanks to…
Kansas Fertilizer Research Fund
Co-operating Farmers
Fellow research group workers
