Nitrogen in the Environment: Sources, Problems, and Management

Nitrogen (N) is applied worldwide to produce food. It is in the atmosphere, soil, and water and is essential to all life. N for agriculture includes fertilizer, biologically fixed, manure, recycled crop residue, and soil-mineralized N. Presently, fertilizer N is a major source of N, and animal manure N is inefficiently used. Potential environmental impacts of N excreted by humans are increasing rapidly with increasing world populations. Where needed, N must be efficiently used because N can be transported immense distances and transformed into soluble and/or gaseous forms that pollute water resources and cause greenhouse effects. Unfortunately, increased amounts of gaseous N enter the environment as N2O to cause greenhouse warming and as NH3 to shift ecological balances of natural ecosystems. Large amounts of N are displaced with eroding sediments in surface waters. Soluble N in runoff or leachate water enters streams, rivers, and groundwater. High-nitrate drinking water can cause methemoglobinemia, while nitrosamines are associated with various human cancers. We describe the benefits, but also how N in the wrong form or place results in harmful effects on humans and animals, as well as to ecological and environmental systems

Potential Tetany Hazard of N-Fertilized Bromegrass as Indicated by Chemical Composition

The objective of this field experiment was to determine the effect of N fertilization on yield and chemical composition of smooth bromegrass (Bromus inermis L.) and the potential for grass tetany hazard in the northern Great Plains as indicated by chemical composition of bromegrass forage. Chemical components of forage considered in relation to the hazard of tetany (a metabolic disorder of ruminants resulting from forage with low Mg availability) were inorganic cations, organic anions, aconitate, and % total N/% total water-soluble carbohydrate ratio (N/TWSC). Soil was Parshall fine sandy loam, a pachic haploborall. Yields and chemical composition of oven dried forage from plots not previously harvested were determined at approximately 3-week intervals beginning May 9. Differences between the sum (in meq/kg) of inorganic cations (Na+, K+, Ca²+, Mg²+) and inorganic anions (Cl-, No?-, H?PO?-, SO?²-) in forage was defined as the concentration of organic anions (C-A). Mature forage yield obtained from the unfertilized check plot treatment on July 29 was only 29 and 22% of yields obtained from plot treatments fertilized with 90 and 270 kg N/ha, respectively. The K/(Ca+Mg) ratios and K concentrations increased during May and early June, resulting in a K/(Ca+Mg) ratio near or above 2.2 during June and early June in oven dried forage from fertilized treatments. Potassium, expressed as a fraction K/C of the total cations (C), accounted for 35 to 74% of the cationic charge. Fertilization with N increased total N and K concentration and K/C in the forage. As K/C increased, Mg/C and Ca/C decreased and K/(Ca+Mg) increased. Aconitate and C-A concentration correlated highly with K concentration and were increased by N fertilization. Aconitate levels exceeded 1% on May 28; the 270 kg N-treatment remained above 1% through July. Nitrogen fertilizer increased N/TWSC in spring-harvested forage, compared to unfertilized forage, and greatly accentuated the peak N/TWSC values occurring in late spring samples. This study indicated that although potential for increased forage and livestock-carrying capacity with N fertilization is tremendous, N-fertilization may result in a potential tetany hazard to ruminants. Therefore, management practices are needed which minimize tetany hazard while bromegrass yields are increased by N fertilization

nitrogen in the environment : sources, problem, and management

xvi, 702hlm,;21c

Soil fertility and organic matter as critical componennnts of production systems

ix+166hlm.;23c