Introduction The microorganisms in agricultural soils are affected by several factors, such as manuring, cultivation, croprotation and weather conditions. The factors all affect soil fertility and productivity (Alexander, 1977). Soil microorganisms play an important role in the growth of plants and they are responsible for e.g. the decomposition of dead material and for nutrient transformation. The understanding of nutrient transformations (e.g. carbon and nitrogen turnover) in complex systems such as a soil requires information about microbial biomass, microbial activity and enzymatic activity as well as nitrogen processes. In most soils the microbial biomass comprises about 1-3% of the total soil organic matter and there is a reasonably close linear relationship between amounts of biomass and amounts of soil organic matter (Jenkinson & Ladd, 1981). The microbial biomass responds much more quickly than does soil organic matter as a whole to changes in soil management. The long-term effects of organic manure and NPK fertilizers on soil microorganisms have been examined to some extent in long-term fertilization experiments at Askov Experimental Station (e.g. Eiland 1980, 1981). Furthermore, the effects on soil microorganisms of the addition of various compounds (e.g. sewage sludge, heavy metals, pesticides and oil) to the fields can be evaluated by microbiological methods. In pig- and cattle buildings, the dry powder Stalosan ® F (Sta.-F) is used as a hygiene agent. The residues from the product remaining in the slurry will be transported from the animal house to the slurry tank and finally to the field. The positive effect of Sta.-F as a hygiene agent in reducing the number of bacteria, fungi, virus and sporulation rates of unsporulated coccidians oocysts from infected chickens (the coccidians infect the intestinal or blood cells and causing coccidioses) has been documented in several studies performed at different international and national laboratories for the company Stormøllen A/S. The effect of Sta.-F is obtained by an adsorptive bond of the pathogens to the minerals in the product, which is suppose to cause a strong reduction of the these organisms on surfaces of animal houses (Methling et al., 1997). Furthermore, the disinfectant has proved useful in reducing moisture, ammonia emission and H2S in animal buildings. It has also been shown that adding Sta.-F to cattle slurry can reduce ammonia emission by up to 60% (Anderson, 1994). The product both absorbs ammonia and reduces the conversion of urea to ammonia. However, very little has been known about the long-term effect of Sta.-F on the soil environments, when the residues of the product will be applied to the field through the slurry for many years. The main purpose of this study was to examine the microbiological and chemical conditions in the soil after using St.-F in animal houses with pigs (sows and piglets) and after adding Sta.-F directly to the slurry immediately before the slurry was transferred to field plots. The experiment also included plots receiving only inorganic fertilizer and a combination of inorganic fertilizer and Sta.-F. In addition, chemical and microbiological tests were performed on the different slurry types, and crop yields and Cu content in the crop were also measured. Material and methods Slurry types and addition of Stalosan ® F Slurry 1 (Foulum slurry) Different amounts of Sta.-F. were added to the slurry from a pigfarm: 1) without addition of Sta.- F, 2) addition of 0.5 kg Sta.-F T -1 slurry (normal amount) and 3) addition of 5 kg Sta.-F T -1 slurry (10 times normal amount). This farm does not use Sta.-F in the animal building. The amount of Sta.-F added to the slurry to reflect the real situation in agriculture, was calculated from the amount of Sta.-F given as 50 g per m 2 and number of times per week in the animal building. Slurry 2. From a pigfarm (sows with piglets), where the farmer frequently used Sta.-F in the animal building.
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