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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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warm (April to October) seasons. Table D-2 reports the results of our calculations.

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The first finding, which is readily apparent, is the seasonal (i.e. temperature) effect on the mineralization rates. The rates are much lower in winter and early spring months than during the growing season. The authors report that 1993 had a cold wet spring and much moisture into June and July. One might anticipate denitrification under these conditions, but the greater yield for the November manure application would seem to indicate that the problem was lack of N mineralization. The authors estimated that only 75 lbs ac-1 (84 kg ha-1) was available from the November manure applications and only 40 lbs ac-1 (45 kg ha-1) for the winter and spring manure applications. Our figures indicate that even less N was available for the April manure application in 1993.

In all, the N mineralization rates indicated by the data from the Wisconsin study are probably low because additional N was likely mineralized and either leached as nitrate or denitrified as nitrogen gases to the atmosphere. Nevertheless, the k values calculated for the growing season (i.e. the April manure application) certainly fall within the range of those calculated from the Pratt et al. (1973) decay series (0.00061 to 0.0038 day-1). The effect of temperature is evident by the N mineralization rates of cold (Nov – April) and warm (April through October) seasons as well as the problems encountered in the years 1993 and 1995 with cold wet springs and early summers. In addition to soil temperature, the other factors highlighted in the literature as influencing microbial activity and mineralization are soil moisture, pH, characteristics of the substrate, and management practices.

D-4 A study from Stephenville, Texas (Haney et al., 1996) was also used for comparison of k values. Dairy manure, not described further, was applied at rates of 0, 75, 150, and 300 lbs N per acre (84, 168, 337 kg ha-1) on plots used either to grow coastal Bermuda grass or a dual crop of wheat and coastal Bermuda grass. Considering the similarities in climatic conditions and dairy operations in Texas and California, the dairy manure in Texas would be comparable to solid dairy manure collected in Central Valley of California. The investigators measured the initial inorganic N in the soil, the total N uptake by the crops, and the N mineralized. The N mineralized may be determined by mass balance that included the initial soil N, the N from the manure, and N uptake by plants. Thus, total N mineralized from dairy manure treated plots minus the N mineralized in the control plots equals the N mineralized from manure. Haney et al.

(1996) results are reproduced in Table D-3 and the resulting k values and N mineralization half-life are summarized in Table D-4.

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D-5 Again, assessment of the data from the Texas study show that the k values calculated for the growing season certainly fall within the range of those calculated from the Pratt et al.

(1973) decay series (0.00061 to 0.0038 day-1). Using Haney et al. (1996) data for total N mineralized there seems to be a pattern of decreasing N mineralization rates as the total N in the manure increases. This is logical as the microbial decomposition processes may be affected by factors other than amounts of substrates. Excessive application of manure may simply overload the system and not provide additional available N to the crops.

Van Kessel and Reeves (2002) represents perhaps the most complete recent study on the mineralization of nitrogen in dairy manure. They collected 107 samples of manure from five eastern states, which had wide ranges of composition: 14 to 386 g dry matter kg-1;

0.9 to 9.5 kg total N m-3; and 0.3 to 4.9 kg NH4+-N m-3. These samples were incubated aerobically for 56 days at 25 °C and sampled for NH4+-N and NO3--N on days 2 and 56.

Net N mineralization ranged from –29.2% (i.e. immobilization of NH4+-N) to +54.9% of total N. There appeared to be no simple straightforward relationship between the composition of manure and the extent of N mineralization. Even though there is no significant correlated relationship with the components, one of the better r-values obtained was the C/N ratio with r =0.348. The histogram of the results appears to provide a normal relationship with an average mineralization of 12.8%. Calculation of k values and half-life from this provides k = 0.0024 day-1 with a half-life of 283 days -easily comparable to the results from the field studies presented earlier. The range in half-life is from infinite to 49 days.

Van Kessel et al. (2000) provided data for the mineralization of components found in manure. Calculations for the k values and half-life of these components are presented in Table 6-5 below. One may observe a close but not perfect relationship between the C to N ratio and the half-life for nitrogen mineralization. The values for neutral detergent fiber (NDF) and acid detergent fiber (ADF) were not calculated since there was a net immobilization of N for these components. One might expect this from material that had high C/N ratio.

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Nakamura and Harter (Appendix H) used field data from a study in Merced County (Harter et al., 2001; Campbell-Mathews, 2004). They constructed a site-specific fully transient unsaturated zone flow and transport model that was calibrated against a threeyear time series of soil moisture and soil ammonia measurements and against groundwater nitrate measurements. The program HYDRUS (Šim nek et al., 1998) was used for the modeling. It operates similar to ENVIRO-GRO (Appendix E), except that it does not allow for simulation of plant stress conditions. Transient water flow and nitrogen transformation and transport was modeled. The model also accounted for plant nitrogen uptake assuming that the crop was neither water nor nutrient stressed.. Nitrogen transformations were handled as described above and also accounted for the sorption of organic N and ammonia-N.

The model was used to estimate mineralization, nitrification, and denitrification rates by calibration against a large set of soil nitrogen and groundwater nitrate data. A sensitivity analysis was implemented to investigate the sensitivity of the estimated parameters to the model structure. The results confirmed that denitrification and/or volatilization from the root zone and even during the application of the diluted manure water was negligible at the site and that nitrification of ammonia is relatively rapid (less than 2-3 months half-life) and affected all of the organic manure. This apparently rapid mineralization of organic N may be partly due to high permeability and hence good aeration of the fine sandy textured soils at the field site. It is possibly due also to mineralization of residual organic N from manure applications in years prior to the experiment, which had seen significantly higher amounts of organic N applications.

Several other studies have shown cases in which manure led to significant denitrification (Calderon et al., 2004). However, the work by Nakamura and Harter was for very sandy, excessively drained soils.

D-7 With respect to mineralization rates (eq. D-1), the analysis by Nakamura and Harter (Appendix H) also indicates that mineralization of the applied organic manure was relatively rapid (less than 2-3 months half-life) and affected all of the organic manure (all manure organic N was found labile). This apparently rapid mineralization of organic N may be partly due to high permeability and hence good aeration of the fine sandy textured soils at the field site. It is possibly also due to mineralization of residual organic N from manure applications in years prior to the experiment, which had seen significantly higher amounts of organic N applications.

In support of complete, relatively rapid mineralization under California conditions is a recent review of biosolids N mineralization by Crohn (Appendix I). Biosolids (human waste from wastewater treatment plants) are essentially similar in organic N composition to animal manure. Hence, the mineralization rates of organic N in animal manure would be expected to be of similar order of magnitude as that of organic N in biosolids.

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2. Calderon, F.J., G.W. McCarty, J.A.S. van Kessel, and J.B. Reeves, III. 2004.

Carbon and nitrogen dynamics during incubation of manured soil. Soil Sci. Soc.

Am. J. 68(5): 1592-1599.

3. Campbell-Mathews, M., 2004. Principles of recycling dairy manures through forage crops. Proceedings, National Alfalfa and Forage Symposium, 14-15 December, 2004, San Diego, CA, http://alfalfa.ucdavis.edu. 8 pages.

4. Deans, J.R., J.A.E. Molina and C.E. Clapp. 1986. Models for predicting potentially mineralizable nitrogen and decomposition rate constants. Soil Sci. Soc.

Am. J. 50:323-326.

5. Haney, R.L., F.M. Hons, M.A. Sanderson, G.W. Evers and D.A. Zuberer. 1996.

Nitrogen mineralization from dairy manure and associated coastal bermudagrass nitrogen uptake. pp 77-84 In G. W. Evers ed. Forage Research in Texas, 1996.


6. Harter, T., H. Davis, M.C. Mathews and R.D. Meyer. 2002. Shallow groundwater quality on dairy farms with irrigated forage crops. J. of Contaminant Hydrology 55 (3-4), pp. 287-315.

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8. Paustian, K., W.J. Parton and J. Persson. 1992. Modeling soil organic matter in organic amended and nitrogen fertilized long-term plots. Soil Sci. Soc. Am. J.


9. Pratt, P.F., F.E. Broadbent and J.P. Martin. 1973. Using organic wastes as nitrogen fertilizers. California Agriculture, June (pp.10-13).

10. Pratt, P.F., S. Davis and R.G. Sharpless. 1976b. A four-year field trial with animal manures I. Nitrogen balances and yields. II. Mineralization of nitrogen.

Hilgardia 44:99-125.

11. Pratt, P.F., S. Davis, R.G. Sharpless and S. E. Bishop 1976a. Nitrate contents of sudangrass and barley forages grown on plots treated with animal manures.

Agron. J. 68:311-314.

12. Salter, R.M. and T.C. Green. 1933. Factors affecting the accumulation and loss of nitrogen and organic carbon in cropped soil. J. Am. Soc. Agron. 25:622-630.

13. Šimùnek, J, M. Sejna, and M.Th. van Genuchten. 1998. The HYDRUS-1D software package for simulating the one-dimensional movement of water, heat, and multiple solutes in variably-saturated media Version 2.0. U.S. Salinity Laboratory: 178p.

14. Smith, J.L., B.L. McNeal, H.H. Cheng and G.S. Campbell. 1986. Calculation of microbial maintenance rates and net nitrogen mineralization in soil at steady-state.

Soil Sci. Soc. Am J. 50:332-338.

15. Smith, S.J. and E.A. Paul. 1990. The significance of soil microbial biomass estimations p 357-396. In J.M. Bollag and G. Stotzky (ed.) Soil Biochemistry.

Vol. 6, Marcel Dekker, Inc. New York, N.Y.

16. Stanford, G. and S.J. Smith.1972. Nitrogen mineralization potentials of soils. Soil Sci. Soc. Am. Proc. 36:465-472.

17. Talarczyk, K.A., K.A. Kelling and T.M. Wood. 1996. Timing of manure applications to cropland to maximize nutrient value In Core4 Conservation for Agricultures Future.


18. Van Kessel, J.S., J. B. Reeves III and J.J. Meisinger. 2000. Nitrogen and carbon mineralization of potential manure omponents. J. Environ. Qual. 29:1669-1677.

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G. L. Fenga, J. Leteya*, A.C. Changa, and M. Campbell-Mathewsb a Department of Environmental Sciences, University of California, Riverside, CA 92521 b University of California Cooperative Extension, 733 Country Center III Ct. Modesto, CA 95355 Abstract Large scale dairy operations are common. In many cases the manure is deposited on a paved surface and then removed with a flushing system, after which the solids are separated, the liquid stored in ponds, and eventually the liquid applied on adjacent crop land. Management of liquid manure to maximize the fertilizer value and minimize water quality degradation requires knowledge of the interactive effects of mineralization of organic N (ON) to NH4+, crop uptake of mineral N, and leaching of NO3 on a temporal basis. The purpose of the research was to use the ENVIRO-GRO model to simulate how the amount of applied N, timing of N application, ON mineralization rates, chemical form of N applied, and irrigation uniformity affected (1) yields of corn (Zea mays) in summer and a forage grass in winter in a Mediterranean climate and (2) the amount of NO3 leached below the root zone. This management practice is typical for dairies in the San Joaquin Valley of California. The simulations were conducted for a ten-year period.

Steady state conditions, whereby an equivalent amount of N applied in the organic form will be mineralized in a given year, are achieved more rapidly for materials with high mineralization rates. Both timing and total quantity of N application are important in affecting crop yield and potential N leaching. Major conclusions from the simulations are as follows. Frequent low applications are preferred to less frequent higher applications. Increasing the amount of N application increased both the crop yield and the amount of NO3 leached. Increasing irrigation uniformity increased crop yields but had variable effects on the amount of NO3 leached. A winter forage crop following a summer corn crop effectively reduced the leaching of residual soil N following the corn crop.

Key words: Nitrate, manure, groundwater, organic nitrogen, mineralization, leaching.

* Corresponding author. John.Letey@ucr.edu E.1 Introduction Livestock and dairy production around the world is progressively moving toward congregating a large number of animals into small land areas. For example, dairies in California have a total herd size of 1.5 million cows. In 1999 the average size of California's 2200 dairy farms was over 650 milk cows, not including dry stocks, heifers, and calves (CDFA, 2000).

The feed rations for animals in the confined animal operations are formulated to maximize production. As a result, the large amount of nitrogen-rich wastes produced by the animals must be properly managed to avoid environmental degradation.

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