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¶ Corn, Field (Zea mays)
| Table No: | Growth Stage: | Plant Part: |
| Table A | Emergence to 4-leaf (VE - V4) | Whole plant |
| Table B | 6-leaf to 10-leaf (V6 - V10) | Youngest, mature leaves |
| Table C | 12-leaf to pre-tassel (V12 - V18) | Youngest mature leaves |
| Table D | Tasseling (VT) | Ear leaf |
| Table E | Silking (R1) | Ear leaf |
| Table F | Blister to milk (R2 - R3) | Ear leaf |
| Table G | Post-season (1 to 3 weeks after 80% of kernels have formed black-layer) | Lower stalk segment |
| Table H | Corn Nutrient Uptake |
¶ A. Emergence to 4-leaf (VE - V4)
Plant Part: Whole plant
Sampling Procedure: Collect 20 to 25 plants, cut off at ground level
| Analysis | Tissue Concentration Guidelines (from long-term survey data) | ||||||||
| Very Low to Low | Typical Range | High to Very High | |||||||
| Nitrogen, % N | 3.10 | - | 3.65 | 3.65 | - | 4.80 | 4.80 | - | 5.15 |
| Phosphorus, %P | 0.27 | - | 0.32 | 0.32 | - | 0.48 | 0.48 | - | 0.57 |
| Potassium, % K | 2.60 | - | 3.35 | 3.35 | - | 4.55 | 4.55 | - | 5.00 |
| Calcium, % Ca | 0.35 | - | 0.40 | 0.40 | - | 0.70 | 0.70 | - | 0.85 |
| Magnesium, % Mg | 0.16 | - | 0.18 | 0.18 | - | 0.33 | 0.33 | - | 0.41 |
| Sulfur, % S | 0.20 | - | 0.23 | 0.23 | - | 0.31 | 0.31 | - | 0.35 |
| Zinc, ppm Zn | 22 | - | 28 | 28 | - | 57 | 57 | - | 75 |
| Iron, ppm Fe | 140 | - | 185 | 185 | - | 550 | 550 | - | 890 |
| Manganese, ppm Mn | 45 | - | 60 | 60 | - | 115 | 115 | - | 145 |
| Copper ppm Cu | 6 | - | 8 | 8 | - | 14 | 14 | - | 17 |
| Boron, ppm B | 6 | - | 7 | 7 | - | 17 | 17 | - | 23 |
| Nitrogen-to-sulfur ratio (N:S) | 11 | - | 13 | 13 | - | 17 | 17 | - | 19 |
| Nitrogen-to-potassium ratio (N:K) | 0.8 | - | 0.9 | 0.9 | - | 1.20 | 1.20 | - | 1.40 |
| Sodium, % Na | less than 0.010 | 0.01 | - | 0.015 | 0.015 | - | 0.028 | ||
¶ Figure B.
¶ B. 6-leaf to 10-leaf (V6 - V10)
Plant Part: Youngest, mature leaves
Sampling Procedure: Collect 15 to 20 leaves. Start at the top of the whorl and remove the first leaf with a fully-formed collar (i.e., the "joint" between the leaf and the stem sheath. Discard the collar and submit the leaf blade for analysis.
| Analysis | Tissue Concentration Guidelines (from long-term survey data) | ||||||||
| Very Low to Low | Typical Range | High to Very High | |||||||
| Nitrogen, % N | 2.80 | - | 3.15 | 3.15 | - | 4.20 | 4.20 | - | 4.65 |
| Phosphorus, %P | 0.24 | - | 0.27 | 0.27 | - | 0.37 | 0.37 | - | 0.43 |
| Potassium, % K | 1.95 | - | 2.50 | 2.50 | - | 3.75 | 3.75 | - | 4.00 |
| Calcium, % Ca | 0.25 | - | 0.30 | 0.30 | - | 0.60 | 0.60 | - | 0.75 |
| Magnesium, % Mg | 0.13 | - | 0.15 | 0.15 | - | 0.29 | 0.29 | - | 0.37 |
| Sulfur, % S | 0.17 | - | 0.20 | 0.20 | - | 0.29 | 0.29 | - | 0.33 |
| Zinc, ppm Zn | 17 | - | 20 | 20 | - | 38 | 38 | - | 50 |
| Iron, ppm Fe | 100 | - | 120 | 120 | - | 280 | 280 | - | 400 |
| Manganese, ppm Mn | 45 | - | 55 | 55 | - | 110 | 110 | - | 140 |
| Copper ppm Cu | 6 | - | 8 | 8 | - | 13 | 13 | - | 16 |
| Boron, ppm B | 6 | - | 7 | 7 | - | 17 | 17 | - | 24 |
| Nitrogen-to-sulfur ratio (N:S) | 11 | - | 13 | 13 | - | 17 | 17 | - | 18 |
| Nitrogen-to-potassium ratio (N:K) | 0.9 | - | 1 | 1 | - | 1.30 | 1.30 | - | 1.55 |
| Sodium, % Na | less than 0.010 | 0.01 | - | 0.013 | 0.013 | - | 0.024 | ||
¶ Figure B.
¶ C. 12-leaf to pre-tassel (V12 - V18)
Plant Part: Youngest mature leaves
Sampling Procedure: Collect 15 to 20 leaves. Start at the top of the whorl and remove the first leaf with a fully-formed collar (i.e., the "joint" between the leaf and the stem sheath. If the ear leaf is evident, collect the ear leaf. Discard the collar and submit the leaf blade for analysis.
| Analysis | Tissue Concentration Guidelines (from long-term survey data) | ||||||||
| Very Low to Low | Typical Range | High to Very High | |||||||
| Nitrogen, % N | 2.55 | - | 2.80 | 2.80 | - | 3.40 | 3.40 | - | 3.60 |
| Phosphorus, %P | 0.23 | - | 0.27 | 0.27 | - | 0.35 | 0.35 | - | 0.38 |
| Potassium, % K | 1.80 | - | 2.15 | 2.15 | - | 2.80 | 2.80 | - | 3.10 |
| Calcium, % Ca | 0.23 | - | 0.27 | 0.27 | - | 0.41 | 0.41 | - | 0.51 |
| Magnesium, % Mg | 0.11 | - | 0.13 | 0.13 | - | 0.24 | 0.24 | - | 0.30 |
| Sulfur, % S | 0.16 | - | 0.18 | 0.18 | - | 0.23 | 0.23 | - | 0.25 |
| Zinc, ppm Zn | 16 | - | 19 | 19 | - | 32 | 32 | - | 39 |
| Iron, ppm Fe | 80 | - | 95 | 95 | - | 155 | 155 | - | 200 |
| Manganese, ppm Mn | 40 | - | 50 | 50 | - | 85 | 85 | - | 105 |
| Copper ppm Cu | 6 | - | 7 | 7 | - | 11 | 11 | - | 13 |
| Boron, ppm B | 7 | - | 9 | 9 | - | 22 | 22 | - | 30 |
| Nitrogen-to-sulfur ratio (N:S) | 12 | - | 13 | 13 | - | 17 | 17 | - | 18 |
| Nitrogen-to-potassium ratio (N:K) | 0.9 | - | 1.0 | 1.0 | - | 1.4 | 1.4 | - | 1.6 |
| Sodium, % Na | less than 0.010 | 0.01 | - | 0.011 | 0.011 | - | 0.02 | ||
¶ Figure C.
¶ D. Tasseling (VT)
Plant Part: Ear leaf
Sampling Procedure: Collect 15 to 20 ear leaves. Break off at base of leaf, but do not include collar.Do not sample if brown silks are present.
| Analysis | Tissue Concentration Guidelines (from long-term survey data) | ||||||||
| Very Low to Low | Typical Range | High to Very High | |||||||
| Nitrogen, % N | 2.55 | - | 2.80 | 2.80 | - | 3.40 | 3.40 | - | 3.60 |
| Phosphorus, %P | 0.23 | - | 0.27 | 0.27 | - | 0.35 | 0.35 | - | 0.38 |
| Potassium, % K | 1.80 | - | 2.15 | 2.15 | - | 2.80 | 2.80 | - | 3.10 |
| Calcium, % Ca | 0.23 | - | 0.27 | 0.27 | - | 0.41 | 0.41 | - | 0.51 |
| Magnesium, % Mg | 0.11 | - | 0.13 | 0.13 | - | 0.24 | 0.24 | - | 0.30 |
| Sulfur, % S | 0.16 | - | 0.18 | 0.18 | - | 0.23 | 0.23 | - | 0.25 |
| Zinc, ppm Zn | 16 | - | 19 | 19 | - | 32 | 32 | - | 39 |
| Iron, ppm Fe | 80 | - | 95 | 95 | - | 155 | 155 | - | 200 |
| Manganese, ppm Mn | 40 | - | 50 | 50 | - | 85 | 85 | - | 105 |
| Copper ppm Cu | 6 | - | 7 | 7 | - | 11 | 11 | - | 13 |
| Boron, ppm B | 7 | - | 9 | 9 | - | 22 | 22 | - | 30 |
| Nitrogen-to-sulfur ratio (N:S) | 12 | - | 13 | 13 | - | 17 | 17 | - | 18 |
| Nitrogen-to-potassium ratio (N:K) | 0.90 | - | 1.00 | 1.00 | - | 1.40 | 1.40 | - | 1.60 |
| Sodium, % Na | less than 0.010 | 0.01 | - | 0.011 | 0.011 | - | 0.02 | ||
¶ Figure D.
¶ E. Silking (R1)
Plant Part: Ear leaf
Sampling Procedure: Collect 15 to 20 ear leaves. Break off at base of leaf, but do not include collar.
| Analysis | Tissue Concentration Guidelines (from long-term survey data) | ||||||||
| Very Low to Low | Typical Range | High to Very High | |||||||
| Nitrogen, % N | 2.20 | - | 2.45 | 2.45 | - | 3.05 | 3.05 | - | 3.20 |
| Phosphorus, %P | 0.21 | - | 0.24 | 0.24 | - | 0.32 | 0.32 | - | 0.36 |
| Potassium, % K | 1.65 | - | 1.90 | 1.90 | - | 2.45 | 2.45 | - | 2.65 |
| Calcium, % Ca | 0.30 | - | 0.35 | 0.35 | - | 0.50 | 0.50 | - | 0.60 |
| Magnesium, % Mg | 0.11 | - | 0.13 | 0.13 | - | 0.21 | 0.21 | - | 0.26 |
| Sulfur, % S | 0.14 | - | 0.15 | 0.15 | - | 0.20 | 0.20 | - | 0.21 |
| Zinc, ppm Zn | 14 | - | 16 | 16 | - | 29 | 29 | - | 36 |
| Iron, ppm Fe | 85 | - | 95 | 95 | - | 140 | 140 | - | 185 |
| Manganese, ppm Mn | 35 | - | 45 | 45 | - | 90 | 90 | - | 115 |
| Copper ppm Cu | 6 | - | 7 | 7 | - | 11 | 11 | - | 13 |
| Boron, ppm B | 6 | - | 7 | 7 | - | 18 | 18 | - | 24 |
| Nitrogen-to-sulfur ratio (N:S) | 12 | - | 14 | 14 | - | 17 | 17 | - | 18 |
| Nitrogen-to-potassium ratio (N:K) | 0.90 | - | 1.00 | 1.00 | - | 1.45 | 1.45 | - | 1.60 |
| Sodium, % Na | less than 0.010 | 0.01 | - | 0.015 | 0.015 | - | 0.032 | ||
¶ Figure E.
¶ F. Blister to milk (R2 - R3)
Plant Part: Ear leaf
Sampling Procedure: Collect 15 to 20 ear leaves. Break off at base of leaf, but do not include collar.
| Analysis | Tissue Concentration Guidelines (from long-term survey data) | ||||||||
| Very Low to Low | Typical Range | High to Very High | |||||||
| Nitrogen, % N | 1.80 | - | 2.25 | 2.25 | - | 2.95 | 2.95 | - | 3.20 |
| Phosphorus, %P | 0.16 | - | 0.22 | 0.22 | - | 0.33 | 0.33 | - | 0.38 |
| Potassium, % K | 1.55 | - | 1.75 | 1.75 | - | 2.40 | 2.40 | - | 2.65 |
| Calcium, % Ca | 0.30 | - | 0.37 | 0.37 | - | 0.61 | 0.61 | - | 0.71 |
| Magnesium, % Mg | 0.12 | - | 0.14 | 0.14 | - | 0.26 | 0.26 | - | 0.32 |
| Sulfur, % S | 0.12 | - | 0.15 | 0.15 | - | 0.20 | 0.20 | - | 0.23 |
| Zinc, ppm Zn | 13 | - | 16 | 16 | - | 30 | 30 | - | 40 |
| Iron, ppm Fe | 85 | - | 100 | 100 | - | 165 | 165 | - | 210 |
| Manganese, ppm Mn | 30 | - | 40 | 40 | - | 90 | 90 | - | 120 |
| Copper ppm Cu | 5 | - | 7 | 7 | - | 12 | 12 | - | 15 |
| Boron, ppm B | 4 | - | 7 | 7 | - | 18 | 18 | - | 27 |
| Nitrogen-to-sulfur ratio (N:S) | 11 | - | 13 | 13 | - | 16 | 16 | - | 18 |
| Nitrogen-to-potassium ratio (N:K) | 0.75 | - | 1.00 | 1.00 | - | 1.45 | 1.45 | - | 1.65 |
| Sodium, % Na | less than 0.010 | 0.01 | - | 0.015 | 0.015 | - | 0.027 | ||
¶ Figure F.
¶ G. Post-season (1 to 3 weeks after 80% of kernels have formed black-layer)
Plant Part: Lower stalk segment
Sampling Procedure: Collect 12 to 15 stalk segments throughout field area with similar soil type and mangement history. Using garden shears suggested. Cut 14 inches above ground level. Collect the 8-inch long stalk segment from between 6 to 14 inches above ground level. Do not collect diseased or damaged stalks.Collect separate samples from field areas that differ in soil type or management history.
| Analysis | Tissue Concentration Guidelines (from long-term survey data) | |||||||||
| Low | Marginal Range | Optimal | Excess | |||||||
| Nitrate, ppm NO3-N | ||||||||||
| Iowa State | < 250 | 250 | - | 700 | 700 | - | 2000 | >2000 | ||
| Purdue University | < 450 | 450 | - | 2000 | >2000 | |||||
| Univ. of Nebraska | < 250 | 250 | - | 700 | 700 | - | 2000 | > 2000 | ||
| Wilhelm (Univ. of Nebr.) | < 900 | 900 | - | 2700 | >2700 | |||||
¶ Figure G.
¶ Interpretations
Low: Nitrogen was very likely deficient; additional nitrogen could have likely improved current year's yield.
Marginal: Nitrogen uptake was very close to minimum requirement; evaluate current year and next year's nitrogen management strategy; increase nitrogen?
Optimal: Nitrogen uptake was within range for maximum profits; if yields were low, factors other than nitrogen deficiency are likely causes.
Excess: Nitrogen uptake exceeded requirement for this year's yield; evaluate current nitrogen management strategy for possible adjustments.
NOTE: Interpretations have been developed for corn grown under Midwest Corn Belt conditions. Guidelines and interpretations may differ in other areas, but have not been researched.
Alternative sampling method: Locate first full joint above above brace-root ring. Cut half-way between this joint and next joint up the stalk. Cut half-way between this joint and brace-root ring.
¶ References:
http://www.extension.iastate.edu/Publications/PM1584.pdf
http://www.agry.purdue.edu/ext/corn/news/articles.03/StalkNitrateTest-0915.pdf
Wilhelm, et.al. 2005. Agronomy Journal 97:1502-1507, http://cropwatch.unl.edu/web/cropwatch -- archives 09/12/08