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Estimates of N, P, and K availability to corn (Zea maysL.) 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−1yr−1on 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 MCaCl2solution 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.

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−1liquid 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−1occurred 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 NO3leaching occurred, NO3‐N/Cl ratios decreased with depth under the injection zone. The abundant supply of NO3and readily oxidizable C, combined with the high moisture environment, led to the conclusion that liquid manure injections created an environment conducive for denitrification.

Anaerobically digested liquid sewage sludge was applied to field plots at rates of 0, 3.75, 7.5, 15, 30, and 60 metric tons dry solids/ha on a Warsaw sandy loam and a Piano silt loam during the summer of 1971. Additional experiments were established at both locations in 1972 and 1973 using the same treatment rates. Following sludge application the 1971 and 1972 trials were planted to rye (Secale cerealeL.). After rye forage harvest the following spring, the residual crop responses were tested with corn (Zea maysL.) on the 1971 and 1972 experimental areas for up to 3 years. The 1973 plots were initially cropped to sorghum‐sudan (Sorghum bicolorL. Moench × S. sudaneseP. Stapf.) followed by 1 year of corn. Yields of the first crop following sludge application typically increased significantly up to the 7.5‐metric ton/ha rate on the silt loam soil, and up to the 15‐metric tons/ha rate on the sandy loam soil. This corresponded to an application of 190 and 380 kg/ha of available N, and 183 and 366 kg/ha of total P for the 7.5 and 15 metric tons/ha rates, respectively. In some cases, the 30‐ and 60‐metric tons/ha rates depressed the first crop yields, possibly because of large amounts of soluble salts in the sludge. Residual benefits from sludge were evident for at least 3 years at the higher treatment rates. Increasing rates of sludge generally resulted in marked increases in the concentration of N and P in plant tissue. Total recovery by up to four successive crops averaged about 50% for available N and 7% for P at the low treatment rate, and about 14% for N and 3% for P at the highest treatment rate.

Liquid digested sewage sludge applied at rates from 3.75 to 60 metric ton/ha significantly increased the concentrations of inorganic N, organic N, and Bray P1extractable P in a sandy loam and a silt loam soil in south‐central Wisconsin. Most of the applied inorganic N was as NH4‐N and was nitrified rapidly. At sludge rates of 30 metric ton/ha or more, substantial losses of sludge‐applied N occurred by leaching. Soil solution NO3‐N concentrations exceeded 100 mg/liter at the 120‐ to 150‐cm depth 10 weeks after the first sludge application on the permeable sandy loam, and after about 1 year on the silt loam. The N balance indicated that considerable amounts of N may have been lost by denitrification, volatilization, or both, where > 30 metric ton/ha were applied. Mineralization of organic N was more rapid than previously reported. Up to 50% of the applied organic N was mineralized within 3 weeks after the last sludge application. During the remaining 25 months of the experiment, the mineralization rate was essentially constant at about 250 mg organic N/kg of soil/year at the 60 metric ton/ha sludge rate, and 180 mg organic N/kg of soil/year at the 30 metric ton/ha rate. Sludge applications resulted in immediate marked increases in Bray P1extractable P. However, the extractable P levels decreased with time after sludge application, probably as a result of P fixation. Significant amounts of P remained available for at least 2 years at the higher treatment rates.

Metal concentrations in soil and plant tissue resulting from land application of liquid digested sewage sludge were examined by determining Cu, Zn, Cd, Ni, and Cr in rye (Secale cerealeL.) and sorghum‐sudan (Sorghum bicolorL. Moench × S. sudaneseP. Stapf.) forage tissue, in corn (Zea maysL.) grain and stover, and DTPA‐extractable metals in soil. Four crops were grown successively after the application of up to 60 metric ton/ha (dry solids basis) of liquid sewage sludge on a sandy loam and a silt loam in Wisconsin. In general, the addition of sludge increased the concentrations of Cu, Zn, Cd, and Ni in the vegetative tissue but, except for Zn, the additions had relatively little effect on the metal content of corn grain. Chromium did not accumulate in the tissue or grain. In all cases, concentrations of metals were below levels considered to be toxic to the crops grown. Total recovery of added metals by the four crops was < 1% for Cu, Cd, Ni, and Cr, and 1 to 3% for Zn. Levels of DTPA‐extractable Cu, Zn, Cd, and Ni, but not Cr, increased with sludge treatment. Regression analysis showed that DTPA might be useful as a predictor of metal concentrations in the vegetative portions of the plant. However, the relationships were not the same for different crops. The decreases in metal concentrations in the plant tissue and in DTPA extracts with successive crops indicated reversion to less available forms for Zn, Cd, and possibly Ni. The ratio of Cd:Zn in the tissue was about one‐third that of the sludge for all crops.