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«University of California Division of Agriculture and Natural Resources Committee of Experts on Dairy Manure Management September 2003 February 2004, ...»

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-2 -2 Figure 12(f): Contour maps of root mean square error between measured and calculated total NH4-N concentrations and NO3-N concentrations in soil (kOrg-N = 10000.0).

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-2 -2 Figure 12(g): Contour maps of root mean square error between measured and calculated total NH4-N concentrations and NO3-N concentrations in soil (kOrg-N = 100000.0).

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0.1 0.1 –3 –3

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0.1 0.1 –3 –3

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0.1 0.1 –3 –3

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0.1 0.1 –3 –3

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Figure 20: Cumulative NO3-N flux at the bottom boundary for each crop year. NO3-N loads into groundwater for Corn 99, Winter 00, Corn 00, and Winter 01 were smaller than for Corn 98 and Winter 99. Targeted management of manure was effective for controlling the nitrate groundwater contamination.

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Figure 22: NO3-N load at the bottom (3m depth) into groundwater for each crop year.High NO3-N load for Corn 01 is due to high irrigation water amount (Fig.4).

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I.1 Introduction The Clean Water Act charges the United States Environmental Protection Agency (USEPA) with regulating the disposal of sewage sludges generated during wastewater processing. These sludges are formed by concentrating the inert and organic solids that are either collected with the wastewater or generated during treatment. To help communities dispose of them, the USEPA actively promotes land application of sludges as an economical alternative to landfilling or incineration. Because sludges contain large amounts of the nitrogen, phosphorus, and trace elements needed by growing plants, they are promoted as fertilizers. They also can improve soils as organic amendments in the same way as animal manures (“Standards” 1993). To encourage public acceptance of land application, the USEPA and the wastewater treatment industry often refer to sewage sludges as biosolids (“Biosolids” 1994, “Plain” 1994, Sorber 1994).

Due to their origin in wastewater, biosolids contain a number of pollutants that require special attention. Biosolids contain pathogens, heavy metals, and toxic organic chemicals, along with nutrients that, if over-applied, can harm both people and the environment (“Standards” 1993, “Process” 1995, Committee 1996, Crohn 1996, Harrison et al. 1997).

In general, the relative presence of pathogens, metals, and toxic organics will determine if a product may be put to a particular use, such as forage fertilization or backyard gardening, while the quantity actually applied in a given year or growing season is constrained by the nutrient content, or fertilizer value, of the biosolids.

Because California depends heavily on groundwater, nitrogen limits most land application rates. Over-fertilization with nitrogen often pollutes groundwater with nitrate (Patrick et al. 1987, Follett et al. 1991). Biosolids contain one to ten percent nitrogen on (a dry weight basis) the majority of which is in organic form (“Process” 1995). The balance consists of inorganic nitrogen is in the form of ammonium ( NH 4 ), much of which can volatilize to the atmosphere during the application process, or nitrate ( NO3 ), which leaches readily and can also be lost to the atmosphere through denitrification (“Process” 1995, Crohn 1996). Only inorganic forms are immediately plant-available, but some of the organic nitrogen is converted each year to ammonium in a process called mineralization. Designers add the expected mineralized nitrogen to the inorganic nitrogen contained in the incorporated biosolids to determine application rates appropriate for specific crops.

Little information is available about the rate at which biosolids organic nitrogen is miner

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I.2 Mineralization and Related Processes The organic fraction of biosolids nitrogen refers to that portion that is bound up with carbon compounds. Because plants cannot take it up, organic nitrogen is often referred to as immobilized nitrogen. To be used by plants, organic must be converted, or mineralized, to ammonium ions ( NH 4 ) by soil microbes. Under aerobic, or oxygen rich, conditions, other bacteria may convert the ammonium to nitrate ( NO3 ), a process referred to as nitrification. Both nitrate and ammonium are plant available.

During mineralization, biosolids are used as food by bacteria and other microorganisms.

Soil microbes use biosolids carbon as an energy source while biosolids nitrogen serves primarily as a nutrient for building proteins in new and growing cells. As carbon is used for energy, it is converted to CO2 and released from the soil as a gas. This steadily depletes carbon from the soil. As carbon decomposes, any associated organic nitrogen is mineralized to ammonium. Different forms of carbon are metabolized at different rates, however. Carbohydrates and proteins are decomposed readily while more recalcitrant forms, such as lignin and cellulose, break down more slowly (Terry et al. 1979, Boyle 1990, Lerch et al. 1992).

Environmental conditions also affect mineralization rates which can vary considerably.

The most important factors are biosolids type (Epstein et al. 1978, Parker and Sommers 1983, Garau et al. 1986, “Process” 1995), soil temperature (Terry et al. 1981), soil type (Tester et al. 1977, Magdoff and Amadon 1980, Garau et al. 1986, Dendooven et al.

1995), and moisture (Stanford and Epstein 1974). Other factors, such as application rate and soil pH are generally less important (Tester et al. 1977). Warm well-drained soils promote rapid mineralization rates. Such soils are common in California.

The USEPA has published a table of typical mineralization rates for biosolids (Table 1).

Values found in Table 1 were loosely developed from a series of sixteen week laboratory incubations (Sommers et al. 1981), rather than from field studies. Although Sommers et al. (1981) maintained conditions they considered optimal for mineralization, conditions favoring mineralization can persist well beyond sixteen weeks in many parts of California. Sommers et al. (1981) recommended annual mineralization rates of 40% for aerobically digested biosolids, 15% for anaerobically digested biosolids, and 8% for composts.

They did not specifically develop second year recommendations. The USEPA reduces mineralization rates by half for each additional year after application (Table 1). No justification is given for this approach, although a precedent similar to this began in California.


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Pratt et al. (1973) invented the idea of the decay series to describe the decomposition of biosolids and manure in California soils. They predicted that biosolids from a source they were familiar with would release 35% of its organic nitrogen during the first year after application, 10% of the remaining organic nitrogen during the next year and 5% over the third. An application containing 1000 kg organic nitrogen would therefore mineralize 350 kg, 65 kg, and 29 kg during the first, second, and third years after application. The USEPA included this fundamental approach, which is simple, reasonable, and intuitive, in Table 1. Note that the biosolids product considered by Pratt et al. (1973) was anaerobically digested and that their California decay series is therefore significantly higher than the USEPA’s (“Process” 1995). The particular values that make up the decay series are in doubt, however. Pratt et al. (1973) warn that their decay series “should not be considered appropriate for all municipal sludges.” They admit freely that their values were never tested in the field and recommended long-term trials to validate them. Although the USEPA has not subjected the decay series described in Table 1 to rigorous field testing either, these values for the basis for many, and probably most, current designs.

Mathematical modeling presents a more conceptually coherent alternative to the decay series approach. Mathematical models attempt to summarize the many complex processes we call decay using tractable and measurable parameters. First-order models are most often used to predict decay. The simplest form of first order model lumps all organic nitrogen into a single compartment (Stanford and Smith 1972, Parker and Sommers 1983, Garau et al. 1986, Boyle and Paul, 1989, Federle et al. 1997), N m N o 1 e kt, (1) where N m is the nitrogen mineralized during year t (kg/ha/yr), N o is the initial organic nitrogen mass (kg/ha), and k is the annual mineralization rate (yr-1), a constant. Other investigators represent two compartments (Molina et al. 1980, Lindeman and Cardenas 1984, Lerch et al. 1992, Gilmour et al. 1996), one for a rapidly metabolized, or labile, fraction, and the other for more recalcitrant materials. Both compartments decompose as first order processes, N m N o S 1 e kl t N o 1 S 1 e k r t, (2) where S is the biosolids labile fraction, and kl and k r are annual mineralization rates for the labile and recalcitrant fractions (yr-1), respectively. Gilmour et al. (1996) favor a variation on (2) based on sequential, rather than simultaneous, decomposition of the labile and recalcitrant compartments, an approach similar to Crohn (1996).

I-3I.3 Field Studies

Data from field studies are needed to develop parameter values suitable for California if (1), (2), or similar models are to be used to design application rates. Few such studies have appeared in the literature, however. Artiola and Pepper (1992) conducted a five-year study of land application to a sandy irrigated soil in Arizona. Laboratory tests suggested annual mineralization rates of 65% or greater. Accelerated mineralization was confirmed in the field where it was observed that applications failed to significantly increase the soil total nitrogen pool. Nitrate levels increased substantially, however, confirming that almost all of the applied biosolids had mineralized.

Barbarick et al. (1996) published a study of mineralization rates from biosolids applied to dryland wheat in Colorado. They applied 5 to 6 application during the 11 year study which was hampered since no record was made of the nitrogen present in the experimental plots before applications began. Mineralization rates varied greatly according to application rates and ranged from 13 to 67% during the first year. Experimental error and environmental variability account for much of the observed variability.

Chang et al. (1988) incorporated a biosolids compost and two anaerobically digested biosolids products into a sandy loam soil plots as well as a loam soil plots located at the University of California field station in Moreno Valley, California. Between 1975 and 1983, the investigators harvested three sorghum and eight barley crops. The study included control plots as well as the biosolids-amended plots. The uncomposted biosolids decomposed very rapidly (Decay series: 0.89, 0.30, 0.10, 0.05) while the compost mineralized more slowly (Decay series: 0.47, 0.20, 0.10, 0.05). The authors did not model decomposition as a first-order process.

I.4 Discussion Chang et al. (1988) developed the only scientifically rigorous mineralization values available for designing land application rates field tested in California. The hot irrigated desert climate of Moreno Valley strongly favors mineralization. The decay series reported by Chang et al. (1988) probably overestimates decay in dryland or cooler climates.

Additional studies would help to validate or refute the Moreno Valley numbers.

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Barbarick, K. A., Ippolito, J. A., and Westfall, D. G. (1996). “Distribution and mineralization of biosolids nitrogen applied to dryland wheat.” J. Environ. Qual., 25(4), 796Biosolids recycling: beneficial technology for a better environment.” (1994). EPA 832/R-94/009, U.S. Envir. Protection Agency, Ofc. of Water, Washington, D.C.

Boyle, M. (1990). “Biodegradation of land-applied sludge.” J. Environ. Qual. 19, 640Boyle, M. and Paul, E. A. (1989). “Nitrogen transformations in soils previously amended with sewage sludge.” Soil Sci. Soc. Am. J., 53(3), 740-744.

Chang, A. C., Page, A. L, Lund, L. J., Pratt, P. F. and Warneke, J. E. (1988). “Leaching of nitrate from freely drained-irrigated fields treated with municipal sludges.” Planning now for irrigation and drainage in the 21st century, D. R. Hay, ed., American Society of Civil Engineers, New York, 455-467.

Committee on the Use of Treated Municipal Wastewater Effluents and Sludge in the Production of Crops for Human Consumption, Water Science and Technology Board, Commission on Geosciences, Environment, and Resources, National Research Council. (1996). “Use of reclaimed water and sludge in food crop production.” National Academy Press, Washington, D.C. http://www.epa.gov/owmitnet/pipes/sludmis.htm Crohn, D. M. (1996). “Planning land application rates for agricultural systems.” J. Envir.

Engrg., 122(12), 1058-1066.

Dendooven, L. Merckx, R., and Vlasak, K. (1995). “Limitations of a calculated N mineralization potential in studies of the N mineralization process.” Plant and Soil, 177, 175-181.

Epstein, E., Keane, D. B., Meisinger, J. J., and Legg, J. O. (1978). “Mineralization of nitrogen from sewage sludge and sludge compost.”.” J. Environ. Qual., 7(2), 217-221.

Federle, T. W., Gasior, S. D., Nuck, B. A. (1997). “Extrapolating mineralization rates from the Ready CO2 screening test to activated sludge, river water, and soil.” Environmental Toxicology and Chemistry, 16(2), 127-134.

Follett, R. F., Keeney, D. R., and Cruse, R. M. eds. (1991). Managing nitrogen for groundwater quality and farm profitability, Soil Sci. Soc. Am., Madison, Wisc.

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Gilmour, J. T., Clark, M. D., and Daniel, S. M. (1996). “Predicting long-term decomposition of biosolids with a seven-day test.” J. Environ. Qual., 25(4), 766-770.

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