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Nitrogen is the most widely used fertilizer nutrient. There are several myths about nitrogen fertilizers used to promote various agronomic concepts. For example, that “anhydrous ammonia makes the ground hard”. This Crop File summarizes results of a twenty‐year Kansas State University study that evaluated the impact of different nitrogen fertilizers on soil chemical properties.
After ten and twenty years of measurement, many – but not all ‐ chemical properties were unchanged with nitrogen fertilizer use. The study compared both surface and subsurface chemical properties.
Surface soil acidity increased from long‐term nitrogen applications. Nitrogen use increased grain yields, increasing nutrient removal, and reducing surface concentrations of phosphorus and other essential nutrients. Final results of the study are shown in Tables 1 (ten years) and 2 (twenty years).
¶ Table 1. Chemical Properties of Disturbed Soil Samples as Influenced by 10 Years of Fertilizer Nitrogen Application |
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| Measurement: | Soil pH | Organic matter | CEC* | Nitrate‐ nitrogen | Ammonium‐ nitrogen | Phosphorus | Potassium | Calcium | Magnesium | Sodium | Zinc | Iron | Copper | Manganese | |
| Bray‐1 | Ammonium acetate exchangeable | DTPA extractable | |||||||||||||
| Reporting Unit: | OM% | mEq/100g | NO3‐N ppm | NH4‐N ppm | P ppm | K ppm | Ca ppm | Mg ppm | Na ppm | Zn ppm | Fe ppm | Cu ppm | Mn ppm | ||
| Surface: 2.5 to 5.5 in. | |||||||||||||||
| Check (no N) | 6.4 | 2.3 | 22 | 4 | 10 | 27 | 179 | 3540 | 732 | 46 | 0.86 | 53.4 | 1.6 | 23 | |
| Anhydrous ammonia | 5.7 | 2.3 | 22 | 9 | 24 | 23 | 142 | 3401 | 667 | 30 | 0.72 | 67.2 | 2.0 | 36 | |
| Ammonium nitrate | 5.7 | 2.4 | 22 | 8 | 26 | 22 | 156 | 3355 | 695 | 29 | 0.73 | 56.9 | 1.9 | 38 | |
| Urea | 5.7 | 2.4 | 21 | 11 | 25 | 22 | 141 | 3407 | 659 | 30 | 0.72 | 53.9 | 1.8 | 39 | |
| UAN solution | 5.7 | 2.4 | 22 | 12 | 31 | 22 | 150 | 3480 | 633 | 33 | 0.69 | 64.0 | 1.8 | 37 | |
| Significant difference? | |||||||||||||||
| Check vs. fertilizers | yes | no | no | no | yes | no | no | no | no | no | yes | no | no | yes | |
| Within fertilizers | no | no | no | no | no | no | no | no | no | no | no | no | no | no | |
| Subsurface: 8.3 to 11.5 in | |||||||||||||||
| Check (no N) | 6.4 | 2.0 | 25 | 4 | 9 | 14 | 148 | 4372 | 1034 | 81 | 0.58 | 49.0 | 1.9 | 19 | |
| Anhydrous ammonia | 5.9 | 2.1 | 26 | 7 | 28 | 12 | 140 | 4521 | 1001 | 50 | 0.54 | 54.3 | 2.2 | 28 | |
| Ammonium nitrate | 5.8 | 2.2 | 25 | 7 | 27 | 14 | 131 | 3764 | 876 | 41 | 0.47 | 53.9 | 2.0 | 28 | |
| Urea | 5.8 | 2.1 | 24 | 9 | 29 | 13 | 139 | 4053 | 891 | 53 | 0.50 | 52.4 | 1.8 | 27 | |
| UAN solution | 5.9 | 2.1 | 24 | 7 | 30 | 15 | 130 | 4185 | 910 | 56 | 0.47 | 50.5 | 1.8 | 27 | |
| Significant difference? | |||||||||||||||
| Check vs. fertilizers | yes | no | no | yes | yes | no | no | no | no | no | no | no | no | no | |
| Within fertilizers | no | no | no | yes | no | no | no | no | no | no | no | no | yes | no | |
| *CEC = Cation Exchange Capacity | |||||||||||||||
¶ Table 2. Chemical Properties of Disturbed Soil Samples as Influenced by 20 Years of Fertilizer Nitrogen Application |
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| Measurement: | Soil pH | Organic matter | CEC* | Nitrate‐ nitrogen | Ammonium‐ nitrogen | Phosphorus | Potassium | Calcium | Magnesium | Sodium | Zinc | Iron | Copper | Manganese | |
| Bray‐1 | Ammonium acetate exchangeable | DTPA extractable | |||||||||||||
| Reporting Unit: | OM% | mEq/100g | NO3‐N ppm | NH4‐N ppm | P ppm | K ppm | Ca ppm | Mg ppm | Na ppm | Zn ppm | Fe ppm | Cu ppm | Mn ppm | ||
| Surface: 2.5 to 5.5 in. | |||||||||||||||
| Check (no N) | 6.2 | 2.0 | 23 | 4 | 5 | 38 | 220 | 2949 | 548 | 25 | 1.23 | 52.8 | 1.63 | 15 | |
| Anhydrous ammonia | 5.2 | 1.8 | 23 | 27 | 9 | 27 | 217 | 2601 | 459 | 15 | 1.20 | 75.9 | 1.99 | 40 | |
| Ammonium nitrate | 5.2 | 2.3 | 22 | 21 | 11 | 26 | 220 | 2443 | 432 | 14 | 1.11 | 73.4 | 2.10 | 44 | |
| Urea | 5.1 | 2.3 | 23 | 31 | 12 | 24 | 210 | 2566 | 478 | 15 | 1.07 | 75.7 | 2.10 | 51 | |
| UAN solution | S.2 | 2.0 | 22 | 20 | 8 | 28 | 204 | 2494 | 425 | 15 | 1.02 | 77.8 | 1.89 | 38 | |
| Significant difference? | |||||||||||||||
| Check vs. fertilizers | yes | no | no | yes | yes | yes | no | yes | yes | yes | no | yes | yes | yes | |
| Within fertilizers | no | no | no | no | no | no | no | no | no | no | no | no | no | no | |
| Subsurface: 8.3 to 11.5 in | |||||||||||||||
| Check (no N) | 6.4 | 1.5 | 33 | 1 | 5 | 8 | 210 | 3893 | 822 | 71 | 0.48 | 44.7 | 1.94 | 9 | |
| Anhydrous ammonia | 6.0 | 1.3 | 32 | 13 | 5 | 6 | 199 | 3823 | 733 | 40 | 0.36 | 49.4 | 1.90 | 10 | |
| Ammonium nitrate | 6.2 | 1.5 | 34 | 9 | 5 | 6 | 208 | 4060 | 815 | 41 | 0.42 | 43.1 | 1.93 | 7 | |
| Urea | 6.0 | 1.5 | 33 | 10 | 6 | 6 | 212 | 3666 | 719 | 42 | 0.38 | 45.4 | 1.99 | 16 | |
| UAN solution | 6.2 | 1.4 | 31 | 9 | 5 | 5 | 209 | 3949 | 808 | 40 | 0.33 | 39.0 | 1.80 | 7 | |
| Significant difference? | |||||||||||||||
| Check vs. fertilizers | yes | no | no | yes | no | no | no | no | no | yes | no | no | no | no | |
| Within fertilizers | no | no | no | no | no | no | no | no | no | no | no | no | no | no | |
| *CEC = Cation Exchange Capacity | |||||||||||||||
Darusman, Stone, Whitney, Janssen, and Long. 1991. Soil properties after twenty years of fertilization with different nitrogen sources. Soil Sci. Soc. Am. Journ. 55:1097‐1100.
Intrawech, Stone, Ellis, and Whitney. 1982. Influence of fertilizer nitrogen source on soil physical and chemical properties. Soil Sci. Soc. Am. Journ. 46:832‐836.