Ammonia (NH3) emissions from poultry farming operations have become a crucial concern due to their potential adverse effects on performance, birds and human health, and the environment. Due to genetic improvements, current commercial poultry require high quality balanced nutrition to maintain their rapid growth and production. Amino acids are components of protein nutrition that greatly influence the growth of the birds, and methionine is the first limiting essential amino acid in the high protein diets of poultry. However, excess or misuse of amino acid supplementation to poultry diets increases nitrogen (N) excretion and emissions to the environment. Currently, there are limited numbers of research publications regarding NH3 emissions from poultry manure, and few of them address manure enhancement by microbial nitrification. Therefore, the aim of this review is to evaluate the potential of soil nitrifying bacteria to reduce NH3 volatilisation and enhance N retention in poultry manure. This review presents the current status of knowledge regarding soil nitrifying bacteria, NH3 nitrification, and summarises the strategies to enhance microbial nitrification of poultry manure, and the environmental ramifications when using different techniques to control NH3 emissions. In spite of the fact that there are few research studies on reducing NH3 volatilisation through nitrification, it has been concluded that nitrification would be a sustainable method for mitigating N excretion and NH3 emission from poultry; however, further research is needed to identify the proper nitrifying bacteria to enhance microbial nitrification.

The main objective of this experiment was to monitor the impact of barn side and dietary crude protein (CP) on production performance, manure production and composition, and ammonia nitrogen (N) emission from a lactating dairy herd housed in a free-stall barn and managed under farm-like conditions throughout a number of months in each season of the year. The 78-cow lactating herd of the University of Wisconsin-Platteville (USA) was halved and each group was allocated to either the north or south side of the barn and either a recommended (REC) diet with 16.7 ± 1.3% CP dry matter basis (DM) or an excess (EXC) CP diet containing 1.5 units of CP above the REC diet (18.2 ± 1.5%). In 7 months between February 2004 and January 2005, total manure collection was conducted by manual scraping of the alleys and ammonia-N emission was calculated as intake N + bedding N – milk N – scraped manure N. Side of the barn (northern v. southern exposure) did not influence measurements and there was no effect of dietary CP on dry matter intake (DMI), milk, milk fat, and milk protein production, but a lower manure N concentration was observed for the group of cows fed the REC diet compared with the EXC diet (3.43% v. 3.66% of DM). Nitrogen intake was 63 g/day lower (643 v. 706 g/day), milk N was unaffected (157 g/day), manure N was 32 g/day lower (391 v. 423 g/day), and ammonia-N emission was 34 g/day lower (93 v. 127 g/day) for the group consuming the REC diet compared with the group consuming the EXC diet. There were larger variations in measured responses among months of the year than between level of dietary CP. Wet and dry manure excretions tended to be higher, but manure pH was reduced when corn silage became unavailable and the diet included additional corn grain and alfalfa silage as the only forage source. Prediction of manure N excretion for a group of cow determined as N intake – N milk was 9% higher than current prediction equations of the American Society of Agricultural Engineers. Ammonia-N loss averaged 110 g/day per lactating cow, but ranged from 64 g/day to 178 g/day with no clear seasonal pattern. There was no clear association between barn temperature, manure temperature or manure pH and ammonia-N emission; however, intake N explained 61% of the variation in ammonia-N emission.

Proper estimation of the nitrogen (N) content of poultry manure and proper manure handling are necessary to ensure that application rates minimize emissions from the manure and nitrate leaching into the cropland. Uric acid and undigested proteins are the two main N components in poultry manure that cause ammonia emissions and nitrate leaching in the ground water. The ammonia that is applied to cropland may be 50 to 90% of total N, depending upon the way the manure has been stored or treated. Ammonia and hydrogen sulphide contents have been proven to be useful alternative measures of odour reduction. The order of importance in influencing ammonia formation is : litter pH > temperature > moisture content. Total fixation of ammonia was achieved below pH 4 and temperatures down 10°C are necessary to have a negative effect on degradation and volatilisation. Adsorbants such as sawdust and straw enable the capture some of the readily available N and enable the microbial population to start immobilizing N. The organic fraction of poultry manure had a C/N ratio that varied from 1 to 27:1. Most of the N (approximately 60 – 70%) excreted in poultry manure is in the form of uric acid and urea. Total N, total Kjeldahl N (TKN), organic N, ammonium, nitrate and nitrite are significantly correlated with the amount of N mineralised as well as the fraction of organic N mineralised during incubation. Some useful equations are: Inorganic N (IN) = ammonium + nitrate + nitrite; Total N (TN) = TKN + nitrate + nitrite; Organic N = TKN – ammonium or TN – (ammonium + uric acid) or TN – IN; Available N (AN) = Inorganic N + 0.4 × organic N; Predicted available N (PAN) = 80% Inorganic N + 60% Organic N.