How much nitrogen should I apply to corn?

Corn N rates depend on soil type, previous crop, and N:corn price ratio. On loamy high-yield soils following corn, MRTN rates range 135–190 lb N/acre. Following soybeans: 90–140 lb N/acre.

What is my manure worth in fertilizer value?

Manure value is calculated by multiplying available N, P2O5, and K2O per acre by current fertilizer prices. Use the Manure Nutrient Value Calculator on this page for a live-price calculation.

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.

📋 Nutrient Management · Economics · Crop Staging · Pest & Weed · Soil Health · State Stats

Agricultural Fast Facts

The complete on-farm reference — built on UW-Extension A2809 guidelines and integrated with live commodity and fertilizer prices. Corn N rates, manure nutrient value calculator, P&K by soil test, crop staging, GDU, pest thresholds, herbicide MOA, breakeven calculator, and state production data. Free for farmers.

N:Corn Price Ratio Calculator

Enter your corn price and N fertilizer cost. The ratio determines which MRTN table column to use.

⚡ N:Corn Price Ratio — Live Calculator

Corn Price ($/bu)

N Fertilizer

Fertilizer ($/ton)

$/lb N

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N:Corn Ratio

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Use Table Column

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Interpretation

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Before applying: Subtract legume, manure, and green manure N credits. On loamy soils >10% OM use low end. Sandy soils <2% OM use high end.

Soil Type & Previous Crop	N:Corn Price Ratio
Soil Type & Previous Crop	0.05	0.10	0.15	0.20
Loamy — High Yield Potential
Corn, forage legumes, legume veg, green manures	190 170–210	165 155–180	150 140–160	135 125–150
Soybean, small grains	140 125–160	120 105–130	105 95–115	90 80–105
Loamy — Medium Yield Potential
Corn, forage legumes, legume veg, green manures	145 130–160	125 115–140	115 105–125	105 95–110
Soybean, small grains	130 110–150	100 85–120	85 70–95	70 60–80
Sands / Loamy Sands — Irrigated
All crops	215 200–230	200 185–210	185 175–195	175 165–185
Sands / Loamy Sands — Non-Irrigated
All crops	140 130–150	130 120–140	120 110–130	110 100–120

Legume N Credits

Alfalfa — 1st Year (lb N/ac)

Stand Quality	Fine/Med >8"	Fine/Med <8"	Sandy >8"	Sandy <8"
Good — 4+ plants/ft²	190	150	140	100
Fair — 1.5–4 plants/ft²	160	120	110	70
Poor — <1.5 plants/ft²	130	90	80	40

2nd year after fair/good stand on fine/medium soil: 50 lb N/ac credit.

🌿Other Legume Credits

Soybean (field crop)20 lb N/ac

Pea / Snap / Lima bean20 lb N/ac

Sweet Clover (green manure)80–120 lb N/ac

Red Clover (green manure)50–80 lb N/ac

Alfalfa (green manure)60–100 lb N/ac

Green manure <6" growth40 lb N/ac

No soybean credit on sandy soils. Soybean credit already built into guidelines — do not double count.

Common Fertilizer Products — % Nutrient Content

Product	% N	% P₂O₅	% K₂O	Other	lbs/gal
Nitrogen Sources
Anhydrous Ammonia (AA)	82	0	0	—	—
Urea	46	0	0	—	—
UAN 32%	32	0	0	—	11.1
UAN 28%	28	0	0	—	10.6
Ammonium Sulfate (AMS)	21	0	0	24% S	—
Ammonium Nitrate	34	0	0	—	—
Phosphorus Sources
DAP	18	46	0	—	—
MAP	11	52	0	—	—
MAP + Sulfur (12-40-0-10S)	12	40	0	10% S	—
Triple Superphosphate (TSP)	0	46	0	—	—
10-34-0 liquid	10	34	0	—	11.6
Potassium Sources
MOP (Muriate of Potash)	0	0	60–62	—	—
SOP (Potassium Sulfate)	0	0	50	18% S	—
K-Mag	0	0	22	22% S, 11% Mg	—
9-18-9 starter liquid	9	18	9	—	11.1

Liquid weights: 1 gal water = 8.34 lb · UAN 28% = 10.6 lb/gal · UAN 32% = 11.1 lb/gal · 10-34-0 = 11.6 lb/gal

Live Market Prices

Corn

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$/bu CBOT

Soybeans

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$/bu CBOT

Wheat

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$/bu CBOT

Urea N

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$/ton dealer

P Source

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$/ton MAP+S

MOP (K)

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$/ton

Input Cost Builder

Build your projected cost per acre. N $/lb auto-fills from live fertilizer prices — edit to match your dealer.

🌽 Corn — Cost Per Acre

Nitrogen — Urea 46%

lb N/ac ×$/lb N =—

Phosphate (P₂O₅) — DAP/MAP

lb/ac ×$/lb =—

Potash (K₂O) — MOP

lb/ac ×$/lb =—

Seed

$/ac—

Herbicide / Chemical

$/ac—

Land Rent

$/ac—

Other (machinery, drying, overhead)

$/ac—

Total Cost Per Acre—

Take your cost total to the full break-even tool →
The Break-Even Calculator adds a what-if sensitivity table, profit gauge, and printable report.

→ Open Break-Even Calculator

Soil Test Interpreter

Enter your soil test values — get your P₂O₅ / K₂O recommendation. Uses Bray P1 (standard WI/MN). Olsen P users: multiply × 1.6.

🧮 Soil Test → Recommendation Calculator

Crop

Yield Goal

Bray P1 (ppm)

K (ppm)

P Category

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K Category

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Apply P₂O₅ (lb/ac)

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Apply K₂O (lb/ac)

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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
Corn Yield Goal (bu/ac)	V.Low	Low	Opt	High	V.High	Ex.High
Phosphate (P₂O₅) lb/ac
131–150	95	85	55	30	—	0
151–170	100	90	60	30	—	0
171–190	110	100	70	35	—	0
191–210	115	105	75	40	—	0
211–230	125	115	85	45	—	0
231–250	130	120	90	45	—	0
251–270	140	130	100	50	—	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
Yield Goal (bu/ac)	V.Low	Low	Opt	High	V.High	Ex.High
Phosphate (P₂O₅) lb/ac
46–55	80	70	40	20	—	0
56–65	90	80	50	25	—	0
66–75	95	85	55	30	—	0
76–85	105	95	65	35	—	0
86–95	110	100	70	35	—	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

Crop

Yield / Acre

Field Acres

P₂O₅ /ac

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K₂O /ac

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Total P₂O₅

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Total K₂O

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Plant Population by Row Width

Row Width	20"	28"	30"	32"	36"	38"	40"
Row length for 1/1000 ac	26'1"	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

lbs Harvested

Moisture %

Field Acres

Bu @ 15.5%

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Bu / Acre

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Available Nutrient Content by Manure Type

1st year [2nd year] N available. Solid = lb/ton; Liquid = lb/1,000 gal. Manure analysis strongly recommended — content varies considerably between farms.

Incorporate promptly. Each hour of surface exposure costs significant N through volatilization, especially in warm, windy conditions.

Manure Type	N — 1st yr [2nd yr]			P₂O₅	K₂O
Manure Type	>3 Days	1 hr–3 days	<1 Hour	P₂O₅	K₂O
Dairy
Solid >20% DM (lb/ton)	2 [1]	3 [1]	3 [1]	3	6
Solid 11–20% DM (lb/ton)	2 [1]	2 [1]	3 [1]	3	5
Liquid 4–11% DM (lb/1000 gal)	7 [2]	10 [2]	12 [2]	6	17
Liquid <4% DM (lb/1000 gal)	4 [1]	6 [1]	7 [1]	3	11
Beef
Solid (lb/ton)	3 [1]	4 [1]	5 [1]	6	10
Liquid (lb/1000 gal)	5 [2]	6 [2]	8 [2]	6	12
Swine
Solid (lb/ton)	7 [2]	9 [2]	12 [2]	10	8
Liquid finish indoor (lb/1000 gal)	17 [4]	22 [4]	28 [4]	14	22
Liquid finish outdoor (lb/1000 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

💰 Manure Nutrient Value Calculator

What is your manure worth at today’s fertilizer prices? Enter type, incorporation timing, and application rate — get dollar value per acre and total field savings.

$/lb Nfrom fert.json

$/lb P₂O₅~DAP market

$/lb K₂O~MOP market

Edit any price to match your dealer

Manure Type

Incorporation Timing

Application Rate

Unit

gal/acre

Field Acres

App. Cost ($/ac)

Manure Output by Animal

Animal & Weight	lb/day	ton/year	gal/day	1,000 gal/year
Dairy, 1,400 lb	148	27	17.7	6.5
Beef, 1,100 lb	80	15	9.5	3.5
Swine, 150 lb	9.5	1.7	1.2	0.44
Chicken, 2 lb	0.18	0.033	0.02	0.007
Horse, 1,000 lb	50	9.1	6.0	2.2

Application Rate Calculator

🐄 Application Rate Calculator

# Loads

Load Size

Units

Field Acres

Total Applied

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Application Rate

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Soil pH Targets

🎯Target pH by Crop

Alfalfa6.8

Red Clover6.3

Soybean6.3

Corn (grain or silage)6.0

Wheat / Small grains6.0

Potatoes5.4–5.8

Blueberries / Cranberries4.5–5.5

⚖️Liming Rules (Wisconsin)

Max lime rate (all soils)12 ton/ac

Max lime rate (potatoes)8 ton/ac

Min rate — sandy <1% OM1 ton/ac

Min rate — all other soils2 ton/ac

Lead time before alfalfa6–12 months

Equilibration time2–3 years

Lime Requirement Calculator

🪓 Lime Rate Estimator (SMP Buffer — WI Calibration)

SMP Buffer pH

Target pH

Lime Quality (% CCE)

Tons Pure CaCO₃/ac

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Tons Aglime/ac

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Guidance

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Est. Cost/Acre

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Based on WI A2809 SMP buffer calibration. MN soils may differ by 0.5–1.0 ton/ac — consult UMN Extension for MN-calibrated recommendations.

Micronutrient Reference — WI / MN

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. Note: soil S tests have poor predictive reliability — 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 soils in MN.

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	—
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	—

Corn Growth Stages — Interactive GDU Timeline

Click 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. Click any stage.

Select a stage above to view details

GDU Calculator

☀️ Daily GDU (Base 50°F)

Daily Max (°F)

Daily Min (°F)

Accumulated GDU

Today’s GDUs

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New Total

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Corn Stage

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Soybean Stage

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Spray Conditions

Scouting Conditions — What to Watch Now

Pest scouting priorities change by growth stage. Select your current corn and soybean stages to see what matters most.

Corn Stage

Soybean Stage

🔎 Priority Scouting Items

Select growth stages above to see priority scouting items for this week.

Economic Thresholds — Key Insects

Pest	Crop	Economic Threshold	Timing	Notes
Corn Pests
Black Cutworm	Corn	3 or more cut plants per 100	V1–V5	Monitor after adult flights. Cut plants at/below growing point = dead plant.
Corn Rootworm (adult)	Corn	0.75 beetles per plant + silk clipping <1/2"	VT–R1	Silk clipping at pollination is the critical damage window.
European Corn Borer	Corn	~20% whorl infestation with live borers — non-Bt only	V8–VT	Non-Bt hybrids: treat at ~20% infested plants with live borers (UW A3646). Bt hybrids provide good control — scout refuge strips only.
Western Bean Cutworm	Corn	8% egg mass infestation	Pre-tassel	Targets ear tip and kernels. WBC maps at extension sites.
Japanese Beetle	Corn	3+ beetles/ear, silk <1/2" with poor pollination	VT–R1	Treat only during active pollination (4–5 days).
Soybean Pests
Soybean Aphid	Soybean	250 aphids/plant on ≥80% of plants, increasing	V4–R5	Count 20 plants per field. Only treat if population increasing & before R5.
Bean Leaf Beetle	Soybean	20–30% defoliation	V stages	Pod feeding at R3–R5 can warrant action at lower thresholds.
Japanese Beetle (soybean)	Soybean	20% defoliation before bloom; 15% during/after	V–R6	Canopy closure reduces access — focus on field edges.
Soybean Gall Midge	Soybean	Any presence — no established ET	V1–R2	Emerging pest in MN/WI. Orange larvae at stem base. Scout field edges.
Two-Spotted Spider Mite	Both	25–50% leaf stippling, mites present, hot & dry	R1–R5	Hot dry conditions favor rapid buildup. Check field edges first.

Herbicide MOA Reference — Common Classes

MOA Group	Site of Action	Common AI / Products	Crops	Resistance Notes
Group 9	EPSPS inhibitor	Glyphosate (Roundup)	RR corn & soybean	Most common resistance in WI/MN — confirm weed ID before relying on glyphosate alone
Group 2	ALS inhibitor	Classic (chlorimuron), FirstRate (cloransulam), Pursuit (imazethapyr), Harmony GT (thifensulfuron)	Corn, soybean, others	Widespread resistance in waterhemp, horseweed, giant ragweed
Group 14	PPO inhibitor	Flexstar, Ultra Blazer, Cobra, Authority	Soybean, corn (Authority)	Increasing waterhemp resistance — rotate with other MOAs
Group 5	PSII inhibitor	Atrazine, Aatrex, metribuzin	Corn primarily; metribuzin on soybeans	Some resistance; 1 lb ai/ac annual limit in WI
Group 1	ACCase inhibitor	Select Max, Poast, Assure II	Broadleaf crops	Controls grasses. Little resistance currently in WI/MN
Group 3	Microtubule inhibitor	Treflan, Sonalan (trifluralin)	Soybean, corn	Pre-emergent only. Incorporate into soil.
Group 4	Synthetic auxin	2,4-D, dicamba, MCPA	Corn, small grains; Xtend soybeans	Drift risk high. Strict label requirements. Watch vapor temp.
Group 27	HPPD inhibitor	Callisto, Laudis, Impact, Balance	Corn	Excellent waterhemp activity. Rotate with Group 2 avoided fields.

Waterhemp management priority in WI/MN: Confirmed resistance to Groups 2, 5, 9, 14 (and in some populations, 27) makes waterhemp the highest-resistance-management priority in the region. Use 3+ MOA programs with effective soil residual, and do not rely on post-only programs.

Quick Reference — Conversion Factors

⚖️Volume / Weight

1 bushel corn56 lb

1 bushel soybeans60 lb

1 bushel wheat60 lb

1 bushel oats32 lb

1 bushel barley48 lb

1 gallon water8.34 lb

1 ton2,000 lb

1 MT (metric ton)2,205 lb

🗺️Land / Area

1 acre43,560 ft²

1 acre0.4047 ha

1 section640 acres

1 township36 sections

1 mile5,280 ft

1 ft0.3048 m

1 yd0.9144 m

1 rod16.5 ft

📅Grain Moisture Math

Corn dry @ 15.5%harvest wt × (100-moist)/(100-15.5)

Soybean dry @ 13.0%harvest wt × (100-moist)/87

Shrink (corn 1% moisture)~1.2%

Test weight corn (56 lb target)Low TW = dockage

Drying rule of thumb~0.02 gal propane / point / bu

1 bushel propane4.24 lb

Corn 25%→15.5% (9.5 pts)~0.19 gal propane/bu

1 gal liquid propane4.24 lb / 91,500 BTU

📈Rate / Application

1 oz ai/ac = oz product/acrate ÷ % ai × 100

gal/ac → oz/1000 ft²gal/ac ÷ 43.56 × 128

1 ppm in soil~2 lb/acre × soil wt

1 lb/gal119.8 g/L

Nozzle output (oz/min)speed(mph)×spacing(in)/5940

Seeds per pound — corn~1,400–1,900

Seeds per pound — soybeans~2,400–3,000

🌟Temperature

Soil temp ideal corn germination50°F+

Soil temp ideal soybean germ.50°F+

Frost kills corn (spring)28°F or below

Hard freeze kills soybeans28°F or below

GDU base temp (corn)50°F

GDU max cap (corn)86°F

°F → °C(°F − 32) ÷ 1.8

📙Extension Resources

UW-Extension Soil Fertility (A2809)uwex.edu

UMN Crop Nutrient Mgmtextension.umn.edu

Wisconsin Agronomy Handbooklearningstore.uwex.edu

MN IPM Scout Guideextension.umn.edu

WCROC Crop Reportsswroc.cfans.umn.edu

USDA NASS Crop Reportsnass.usda.gov

Important Dates — WI/MN Crop Calendar

Date / Window	Corn	Soybean	Notes
Apr 20 – May 15	Optimal planting window WI/MN	—	Soil temp ≥50°F at 2" depth for 3 consecutive days
May 1 – May 20	—	Optimal planting window WI/MN	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 north WI/MN
Sep 15	Average first frost (north WI/MN)	Harvest window opens	Frost before black layer can cause quality issues