Effect of a Nitrification Inhibitor on the K, Ca, and Mg Composition of Winter Wheat Forage¹

Abstract

Winter wheat (Triticum aestivum L.) is an important forage for cattle in much of the Southern Great Plains. However, death losses in wheat pastures due to grass tetany of nursing and pregnant older cattle, and frothy bloat of younger cattle, often occur. Forages from fields moderately or heavily fertilized with N are generally more hazardous than forages from unfertilized fields. As regards grass tetany, high rates of N fertilization are particularly hazardous when soil K is high. The objective of the present study was to determine the effect of the nitrification inhibitor nitrapyrin (N‐serve) on the relative uptake of K, Ca, and Mg by winter wheat growing in pots in the greenhouse. When nitrapyrin was added, the plants took up less NO−3‐N because nitrapyrin inhibited nitrification of the added NH+4. The plants also had lower concentrations of K, Ca, and Mg. However, the depression effect was greater for the divalent cations Ca and Mg, than for the monovalent cation K, so the K/(Ca + Mg) ratio was increased. Therefore, when nitrapyrin was added, the forage was more likely to cause grass tetany. Nitrapyrin also decreased plant organic acid concentrations and this probably decreased Mg and Ca uptake. The concentration of K was higher and Mg and Ca was lower during periods of rapid growth. Therefore, the forage was more likely to cause tetany during these periods. Nitrapyrin was effective in delaying nitrification, and this could be useful for supplying N to wheat later in the growing season. However, other steps might have to be taken to avoid an increased incidence of grass tetany.

Management Practices to Overcome the Incidence of Grass Tetany

“…The major difference in N fertilizer sources relating to grass tetany appears to be the relative amounts of NI-l~4 -and NO 3 -N in the fertilizers. Studies with wheat grown in nutrient solutions (Cox and Reisenauer, 1977) and with wheat in soil in the greenhouse (Mathers et al, 1982) showed that NO 3 -N stimulated Mg uptake and increased the concentration of Mg more than did NH~ -N. A study in Louisiana (Table 2) showed similar results with ryegrass in the field (Robinson et al, 1987). Nitrogen fertilizers were applied in multiple applications, at planting in October and after each harvest throughout the growing season.…”

Effect of dicyandiamide on growth and nutrient uptake of cotton

“…The decreased growth resulting from urea fertilization would explain the increases in leaf Ρ, Κ, and Mn concentrations. In addition, NH4 + -N uptake from urea would be expected to increase Ρ concentration (14,15,16) and reduce concentrations of Ca, Mg, and Κ (14,16,17). The inhibitory effect of NH4 + -N uptake on Κ concentrations was diminished by reductions in growth.…”

Influence of Nitrogen Nutrition on the Ionic Balance of Maize Grown in Calcareous Soil

“…It has been reported that the Ratio of (K/Ca + Mg) in forage has a special significance. A ratio of more than 2.2 is considered hazardous and might cause grass tetany (Mathers et al, 1989), the maize in the first stages used forage for animal.…”