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To predict ammonia (NH)) volatilization from field-applied manure, factors affecting volatilization following manure application need to be known. A database of field measurements in the Netherlands was analysed to identify factors affecting the volatilization from manure applied to grassland by various techniques, and to quantify their effects. The application techniques were broadcast surface spreading, narrow-band application, and shallow injection. External factors considered were weather conditions, manure characteristics, soil type and soil moisture content, and grass height. Narrow-band application and shallow injection significantly reduced NH) volatilization, compared with broadcast surface spreading. The mean cumulative volatilization for surface spreading was estimated to be 77% of the total ammoniacal nitrogen (TAN) applied, 20% for narrow-band application and 6% for shallow injection. The TAN content of the manure, the manure application rate and the weather conditions significantly influenced the NH) volatilization rate. The volatilization rate increased with an increase in TAN content of the manure, manure application rate, wind speed, radiation, or air temperature. It decreased with an increase in the relative humidity. The identified influencing factors and their magnitude differed with the application technique. Grass height affected NH) volatilization when manure was applied in narrow bands. The results show that external factors need to be taken into account when predicting ammonia volatilization following manure application.

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Ammonia emission and nutrient load in outdoor runs oflaying hens were measured at a commercial farm with an outdoor run for 3000 hens, and at an experimental farm with two outdoor runs, each for approximately 250 hens. Ammonia emission was recorded at 5, ro, 15 and 20 m from the hen house, using the ventilated chamber technique. Nutrient load was determined by analysing the fresh droppings.The results show ammonia emission to decrease with increasing distance from the hen house. The average emission per hen was 2.0 mg h-I for the run of the commercial farm, and 0.95 and 0.86 mg h-I for the two runs of the experimental farm. The nutrient load within 20 m from the hen house exceeded the threshold value for nutrient supply from manure (170 kg Nand 44 kg P per hal by a factor 15 on both the commercial farm and the experimental farm. The results show that the ammonia emission from the outdoor run oflaying hens was relatively small compared with the emission from the hen house and that the nutrient load in the outdoor run near the house by far exceeded maximum acceptable levels.

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