Manure residual values

Volatilization is the term commonly used for the loss of ammonia gas from surficial soils to the atmosphere the ammonia gas produced has a lower value than the residual ammonium in the soU. Volatilization in farmlands results from applications of urea and manure to fields, and occurs within piles of manure the resulting organic matter may have 6 N values >20%o because of ammonia losses. Ammonium in precipitation derived from volatilazation from waste lagoons can have a distinctive low 6 N value. 

Denitrification causes the 6 N of the residual nitrate to increase exponentially as nitrate concentrations decrease, and causes the acidity of the system to decrease. For example, denitrification of fertilizer nitrate that originally had a distinctive 6 N value of A-0%c can yield residual nitrate with much higher 6 N values (e.g., -K5%o to - -30%o) that are within the range of compositions expected for nitrate from a manure or septic-tank source. Measured enrichment factors (apparent fractionations) associated with denitrification range from —40%o to —5%o hence, the fi N of the N2 is lower than that of the nitrate by about these values. The N2 produced by denitrification results in excess N2 contents in groundwater the fi N of this N2 can provide useful information about sources and processes (Vogel et al., 1981 Bohlke and Denver, 1995). 

Conservative values applicable to traditional farming would be at least 100 kg N/ha a year contributed by clover and 150 kg N/ha for alfalfa grown on cropland pastures—and at least as much as that when planted, as was common both in Europe and in Asia, as green manure winter crops. In contrast, fixation rates in common beans in Latin America, the crop s region of origin, could be less than 10 kg N/ha. Conservative rates for common pulses (lentils, peas, chickpeas) would be below 30 kg N/ha, while values for soybeans could be easily twice as high—but only when virtually all crop residues were also recycled (appendix C). ... 

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