Enter your soil test values. Get your P₂O₅ / K₂O recommendation. Uses the Bray P1 method (common across the Corn Belt). High-pH or Western soils tested by Olsen P: multiply × 1.6.
Soil Test → Recommendation Calculator
P Category
-
K Category
-
Apply P₂O₅ (lb/ac)
-
Apply K₂O (lb/ac)
-
P₂O₅ Cost
-
K₂O Cost
-
Total P+K $/ac
-
Priced from the MAP and potash $/lb in the Economics tab
Soil Test Category Breakpoints (ppm)
Category
Bray P1 (ppm)
K (ppm)
Interpretation
Very Low
<11
<61
Deficient: yield loss likely
Low
11–15
61–90
Below optimum: good response likely
Optimum
16–25
91–130
Sufficient: maintenance rate
High
26–50
131–200
No response expected: reduce or eliminate
Very High
51–75
201–300
No response: draw down levels
Extremely High
>75
>300
Do not apply
Corn P₂O₅ & K₂O Recommendation Tables
Corn Yield Goal (bu/ac)
Soil Test Level
V.Low
Low
Opt
High
V.High
Ex.High
Phosphate (P₂O₅) lb/ac
131–150
95
85
55
30
n/a
0
151–170
100
90
60
30
n/a
0
171–190
110
100
70
35
n/a
0
191–210
115
105
75
40
n/a
0
211–230
125
115
85
45
n/a
0
231–250
130
120
90
45
n/a
0
251–270
140
130
100
50
n/a
0
Potash (K₂O) lb/ac
131–150
85
70
40
20
10
0
151–170
90
75
45
25
10
0
171–190
95
80
50
25
15
0
191–210
105
90
60
30
15
0
211–230
110
95
65
35
15
0
231–250
115
100
70
35
20
0
251–270
120
105
75
40
20
0
Soybean P₂O₅ & K₂O Recommendations
Yield Goal (bu/ac)
Soil Test Level
V.Low
Low
Opt
High
V.High
Ex.High
Phosphate (P₂O₅) lb/ac
46–55
80
70
40
20
n/a
0
56–65
90
80
50
25
n/a
0
66–75
95
85
55
30
n/a
0
76–85
105
95
65
35
n/a
0
86–95
110
100
70
35
n/a
0
Potash (K₂O) lb/ac
46–55
115
100
70
35
20
0
56–65
130
115
85
45
20
0
66–75
145
130
100
50
25
0
76–85
155
140
110
55
30
0
86–95
170
155
125
65
30
0
Olsen P users: Multiply Olsen P × 1.6 to approximate Bray P1.
Nutrients Removed at Harvest
Crop & Component
Yield Unit
lb P₂O₅
lb K₂O
Corn
Corn, Grain
per bu (56 lb @ 15.5%)
0.38
0.29
Corn, Silage
per ton (65% moisture)
3.6
8.3
Corn Stover
per ton DM
4.6
32
Soybean
Soybean, Grain
per bu (60 lb @ 13%)
0.80
1.4
Soybean Straw
per ton DM
5.4
19
Alfalfa & Forage
Alfalfa / Red Clover
per ton DM
13
60
Small Grain Silage
per ton DM
11
44
Small Grains
Wheat, Grain
per bu (60 lb @ 13.5%)
0.50
0.35
Barley, Grain
per bu (48 lb @ 14.5%)
0.40
0.35
Oats, Grain
per bu (32 lb @ 14%)
0.29
0.19
Nutrient Removal Calculator
Field Nutrient Export Estimator
P₂O₅ /ac
-
K₂O /ac
-
Total P₂O₅
-
Total K₂O
-
Plant Population by Row Width
Row Width
20"
28"
30"
32"
36"
38"
40"
Row length for 1/1000 ac
26'2"
18'8"
17'5"
16'4"
14'6"
13'9"
13'1"
Formula: Count plants in that row length × 1,000 = plants/acre. Count at least 3 rows.
Bu/Acre Calculator: Shelled Corn
Corn Yield Calculator
Bu @ 15.5%
-
Bu / Acre
-
Available Nutrient Content by Manure Type
First-year available N [second-year N in brackets] by time to incorporation, then P₂O₅ and K₂O. Solid in lb/ton, liquid in lb/1,000 gal. Book values from UW Extension A2809. Farm manure varies a lot, so a manure test beats this table.
Work it in fast. Manure left on the surface loses N to the air, most in warm, windy weather. The columns show how much.
Manure type
N: 1st yr [2nd yr]
P₂O₅ 1st yr
K₂O 1st yr
Not in 3 days
1 hr–3 days
Within 1 hr
Dairy
Solid, over 20% dry matter (lb/ton)
2 [1]
3 [1]
3 [1]
3
6
Solid, 11 to 20% dry matter (lb/ton)
2 [1]
2 [1]
3 [1]
3
5
Liquid, 4 to 11% dry matter (lb/1,000 gal)
7 [2]
10 [2]
12 [2]
6
17
Liquid, under 4% dry matter (lb/1,000 gal)
4 [1]
6 [1]
7 [1]
3
11
Beef
Solid (lb/ton)
3 [1]
4 [1]
5 [1]
6
10
Liquid (lb/1,000 gal)
5 [2]
6 [2]
8 [2]
6
12
Hog
Solid (lb/ton)
7 [2]
9 [2]
12 [2]
10
8
Liquid, finishing, indoor pit (lb/1,000 gal)
17 [4]
22 [4]
28 [4]
14
22
Liquid, finishing, outdoor storage (lb/1,000 gal)
7 [2]
9 [2]
12 [2]
6
8
Poultry
Chicken, solid (lb/ton)
24 [5]
27 [5]
29 [5]
35
26
Turkey, solid (lb/ton)
26 [5]
28 [5]
31 [5]
35
25
Horse
Solid (lb/ton)
2 [1]
3 [1]
4 [1]
5
6
What is it worth in dollars?Full manure value page: the first-year N, P and K in dollars per 1,000 gal and per ton for every type at dated dealer prices, a worked dairy example on 80 acres, and a calculator that takes your own manure test.
Manure Value Calculator
The N, P₂O₅ and K₂O in the manure at dated dealer prices: an acre, per 1,000 gal or ton, and for the field. Book pounds are first-year; type your own test and every pound counts. The same calculator as on the manure value page.
The calculator needs JavaScript.
Manure Output by Animal
As excreted, before bedding, wash water or rain get in. What goes to storage runs higher.
Cost uses the price you type, for the lime you picked. Aglime prices swing with haul distance, so I don't guess one. With the 98% pelletized option and no price typed, it uses our dealer quote for pelletized lime. Based on UW Extension A2809 SMP-buffer calibration (Upper Midwest). Other regions vary; consult your state land-grant extension for locally calibrated lime recommendations.
Micronutrient Reference: Upper Midwest
Nutrient
Responsive Crops
Deficient
Method
Typical Rate
Key Notes
S
Soybeans, alfalfa, small grains
<10 ppm
KCl
10–20 lb S/ac
Sandy soils, low OM, high rainfall. AMS (24% S) common source. Soil S tests predict response poorly. Apply S on sandy/low-OM soils as insurance regardless of test result.
Zn
Corn, beans, soybeans
<0.5 ppm DTPA
DTPA
1–2 lb Zn/ac
High pH (>7.0), high P, cold wet spring. Corn “white bud.”
B
Alfalfa, clover, sunflower
<0.5 ppm
Hot water
0.5–1 lb B/ac
Sandy soils, low OM. Toxic range narrow. Do not over-apply.
Mn
Soybeans, oats, wheat
<5 ppm DTPA
DTPA
0.5–1 lb Mn foliar
High pH (>6.5), organic soils. Foliar preferred.
Fe (IDC)
Soybeans
pH >7.3 + CaCO₃
SPAD
IDC-tolerant varieties
Most common on calcareous (high-pH) soils.
Tissue Test Critical Levels
Corn: Ear Leaf at R1 (Silking)
Nutrient
Deficient
Sufficient
Excess
N %
<2.7
2.7–3.5
>4.0
P %
<0.25
0.25–0.50
>0.60
K %
<1.7
1.7–2.5
>3.0
S %
<0.15
0.15–0.50
n/a
Zn ppm
<15
15–60
>200
Soybean: Uppermost Trifoliate at R3
Nutrient
Deficient
Sufficient
Excess
N %
<4.0
4.5–5.5
>6.0
P %
<0.22
0.26–0.50
>0.70
K %
<1.4
1.7–2.5
>3.0
Zn ppm
<15
21–55
>100
Fe ppm
<50
51–350
n/a
Corn Growth Stages: Interactive GDU Timeline
Tap any stage to see GDU accumulation, crop description, and key management windows. Based on base 50°F GDUs.
Select a stage above to view details
Soybean Growth Stages: Interactive Timeline
Vegetative (V) and reproductive (R) stages with GDU accumulation from emergence. Tap any stage.
Excellent waterhemp activity. Rotate with Group 2 avoided fields.
Waterhemp management priority across the Corn Belt: Confirmed resistance to Groups 2, 5, 9, 14 (and in some populations, 27) makes waterhemp the highest resistance-management priority in most corn and soybean regions. Use 3+ MOA programs with effective soil residual, and do not rely on post-only programs.
A central Corn Belt timeline. Planting and maturity windows shift roughly one to two weeks per ~150 miles of latitude. Check your state Extension or USDA NASS Crop Progress for local dates.
Date / Window
Corn
Soybean
Notes
Apr 20 – May 15
Optimal planting window
n/a
Soil temp ≥50°F at 2" depth for 3 consecutive days
May 1 – May 20
n/a
Optimal planting window
Soil temp ≥50°F; avoid Sudden Death Syndrome risk from cold early planting
June 1
Significant yield drag begins
Moderate yield drag
~1% yield loss per day after June 1 for corn; beans more flexible to June 10
Late June – July
Critical pollination window
Bloom & pod set
Drought or heat stress during this window has largest yield impact
Late Aug – early Sep
Black layer / physiological maturity
R7 (begin maturity)
Monitor for early frost risk: especially in northern areas
Sep 15
Average first frost (northern areas)
Harvest window opens
Frost before black layer can cause quality issues
State-Level Production Data
U.S. crop production at a glance, with per-state detail from USDA NASS: the national source for acreage, yield, and production across all 50 states.
U.S. Corn: 2025
Production17.0 B bu
Avg yield186.5 bu/ac
Harvested91.3 M ac
U.S. Soybeans: 2025
Production4.26 B bu
Avg yield53.0 bu/ac
Harvested80.4 M ac
National totals: USDA NASS Crop Production 2025 Summary (final). Select any state for its full USDA NASS profile.
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Common questions
How much nitrogen should I apply to corn?
Corn N rates depend on soil type, previous crop, and N:corn price ratio. Corn after corn needs more nitrogen than corn after soybeans, and a high N:corn price ratio points to the low end of the range. Enter your prices in the N:corn ratio calculator and read the MRTN rate tables on this page for your soil and rotation.
What is my manure worth in fertilizer value?
Multiply the first-year available N, and the P2O5 and K2O, in each ton or 1,000 gallons by what those nutrients cost as urea, MAP and potash. The Manure tab has the pounds by manure type and a calculator at live dealer prices. The manure value page at agsist.com/manure-value prices every manure type, an acre and for a whole field.
What is the economic threshold for soybean aphid?
250 aphids per plant on 80% or more of plants, with an increasing population, before R5 growth stage.
How do I calculate growing degree units for corn?
GDU (base 50°F) = [(daily max temp, capped at 86°F) + (daily min temp, floor at 50°F)] / 2 - 50. Accumulate daily from planting.