Estimates of N, P, and K availability to corn (Zea mays L.) from injected dairy manure on three field sites in south central Wisconsin were made using a fertilizer equivalence approach. Nutrient uptake from treatments of a control, three rates of manure (approx. 53, 97, and 138 Mg ha−1 yr−1 on a wet basis), and three rates of broadcast fertilizer were evaluated. Crop nutrient recoveries of fertilizer N, P, and K were generally higher than crop recoveries of manure total N, P, and K. Estimates of first year N, P, and K availability showed substantial variability across rate, location, and year with standard deviations often about 50% of the mean. Ranges for N, P, or K availability were 12 to 63, 12 to 89, and 24 to 153%, respectively. These data do not identify those factors responsible for differences in nutrient availability from one site‐year to another. Biological or chemical availability indices of a 1‐wk anaerobic incubation at 40 °C or a 16‐h autoclaving in 0.01 M CaCl2 solution were evaluated as measures of N availability and compared with field results. Correlations between measured changes in NH4‐N from these indices, as well as total Kjeldahl N and inorganic N levels in the top 30 cm of soil 4 to 6 wk after treatment application, and N uptake indicated inorganic N levels to be a better index of N availability than the other indices examined. However, to determine nutrient availability on a routine basis, more reliable biological or chemical indices are necessary. A simple model may help to simulate environmental effects and the contribution of residual nutrients in the soil.

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A field experiment was conducted on a Piano silt loam (Typic Argiudoll) in southcentral Wisconsin to monitor N transformations following liquid manure injections. Liquid manure with and without a nitrification inhibitor [nitrapyrin, 2‐chloro‐6‐(trichloromethyl)pyridine, 13 mg a.i. L−1 liquid manure] was injected into an uncropped area in June 1985. Soil samples were taken using a grid placed over the vertical cross‐section of the injected bands permitting spatial sampling in the vertical plane. Sampling was done 5, 12, 26, 39, 67, 99, and 350 d after manure application by progressive exposure of the band. Soil water content, pH, NH4‐N, (NO2 + NO3)‐N, Cl, and water‐soluble C were determined. The synagraphic computer program, SYMAP, was used to evaluate spatial changes in inorganic N concentrations in the manure injection zone. Nitrapyrin was not effective in inhibiting nitrification at the rate used. Nitrification occurred at the outer fringes of the band within 5 d; maximum concentrations of 300 to 800 mg NO3‐N kg−1 occurred throughout the injection zone at 26 d. High respiratory activity in the injection zone was indicated by an almost threefold decrease in water‐soluble C between day 5 (750 mg C kg−1) and day 12 (270 mg C kg−1). Water content remained higher than the surrounding soil in the injection zone for 99 d. Once NO3 leaching occurred, NO3‐N/Cl ratios decreased with depth under the injection zone. The abundant supply of NO3 and readily oxidizable C, combined with the high moisture environment, led to the conclusion that liquid manure injections created an environment conducive for denitrification.

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Combining septic tank effluent and animal wastes (mixed wastes) for eventual application to land is being proposed as an alternative wastewater disposal system. Both types of waste are spread on land separately, and private practice may be to mix and spread them together, but in most of the United States mixing of these wastes for land disposal is illegal. No research has been done to assess the hazards associated with spreading mixed wastes on land. The concern is with the impact on public health of adding septic tank effluent to animal wastes for disposal as animal wastes. The effects of pathogens already present in animal waste are presumably allowed for in current U.S. regulations. Pathogens in mixed wastes include viruses, bacteria and parasites. Viruses are not always present in on-site waste disposal systems, but when present are in high numbers. Most viral particles will pass through the septic tank and will remain viable. Transmission will be prevented if these particles are retained in soil or other solids until any of several factors deprive them of infectivity. As animals are the chief reservoir of most enteric bacteria that are pathogenic to man, no additional hazards from bacteria are expected in a mixed waste system. Some parasite eggs and cysts will settle into the bottom of the septic tank, but significant numbers will pass through and will remain viable. Retention with solids will minimize transmission through food and water. In all instances it is important to match land use and waste disposal carefully.