Changes in Soil Attributes Following Low Phosphorus Swine SlurryApplication to No-Tillage Sorghum

lar amounts of total P as TC, but a larger proportion of that P exists as phosphate rather than phytate (Ertl Swine (Sus scrofa) slurry can serve as an excellent fertilizer source. et al., 1998). Bioavailability of P in LPC is higher than Application at rates to meet crop N requirements can result in excess soil P due to low manure N/P ratios. Low phytate corn (LPC) (Zea in TC for nonruminant animals such as swine (Baxter mays L.) stores a greater proportion of P as phosphate than does et al., 1998) and poultry (Ertl et al., 1998). Increased traditional corn (TC) increasing bioavailability of P in pig feed grain. bioavailability of feed P reduces the need for suppleImproved utilization of feed P reduces P concentration in manure and mental P in the diet and results in less P being excreted soil P accumulation. However, the potential effects of LPC manure on by the animal (Baxter et al., 1998). In a laboratory study, other soil properties are not known. Changes in soil attributes over Gollany et al. (2003) found that P content of LPC swine 3 yr were compared for soils receiving LPC manure, TC manure, manure was 42% lower than TC swine manure, but P inorganic fertilizer, and no nutrients in no-tillage sorghum [Sorghum availability was similar. However, potential effects of bicolor (L.) Moench] on a Sharpsburg clay loam (fine, smectitic, mesic LPC swine manure on soil properties have not been Typic Argiudolls). Soil physical properties exhibited values that should adequately assessed in the field. not inhibit crop growth. Several soil chemical properties differed by year and treatment. Particulate organic matter (POM), NO3–N, pH, In addition to nutrients, manure contains organic matand extractable P increased with manure additions. Extractable P conter and minerals. Addition of manure to soils can ditent was greater with addition of TC than LPC manure. Soil chemical rectly or indirectly affect soil physical, chemical, and properties exhibited values acceptable for crop production, but increasbiological properties. Direct effects include changes in ing extractable P increases the potential for environmental contaminanutrient status or pH. Indirect effects may result from tion. Biological soil properties varied in their response to treatments. altered microbial activity, soil organic matter status, and Microbial biomass C decreased in the control and increased in manure rates of nutrient mineralization. In a laboratory study, treatments. The Soil Management Assessment Framework (SMAF) Dendooven et al. (1998) reported that immediately after was used to conduct a dynamic soil quality assessment. The SMAF addition of swine slurry soil pH increased from 6.2 to index values were similar across years in the control and inorganic 7.1, increased to 8.3 after 3 d, and then declined to 7.4 fertilizer treatments and increased in both manure treatments. Manure additions improved soil properties affecting crop production, with P after 28 d. Dendooven et al. (1998) also reported no accumulation and the potential for environmental contamination beincrease in soil NO3–N concentration 28 d after slurry ing lower with LPC manure. LPC manure applied at rates to meet application. Several studies have reported short-term crop N requirements will have slower soil P accumulation rates and increases in microbial biomass C (Lalande et al., 2000; a lower potential for P contamination of the environment. Rochette et al., 2000a), increased enzyme activity (Lalande et al., 2000), and increased C mineralization (Dendooven et al., 1998) following swine slurry addition, but S slurry contains nutrients essential for plant these increases did not persist. Rochette et al. (2000a) growth and when applied to soil at proper rates can described two phases in swine slurry organic matter serve as an excellent source of essential plant nutrients. decomposition. Initial rates of decomposition were When applied to land at rates in excess of that needed rapid, proportional to application rates, and involved by the crop, the potential exists for water soluble P and readily decomposable organic compounds. During the NO3–N to leach and for increased runoff losses of all second phase, decomposition was slower and involved fractions of N and P (Sharpley et al., 1998). Application more recalcitrant compounds. Two months after slurry of swine manure to meet crop N needs can result in the application, microbial biomass C concentrations in soils accumulation of inorganic P because the N/P ratio in receiving swine slurry were similar to those receiving swine manure is lower than that needed by most crops. inorganic fertilizer. Flowers and Arnold (1983) reported The low N/P ratio in swine manure results from the that N-mineralization rates in swine-slurry-amended soil inability of swine to efficiently utilize phytate P, the were similar to untreated controls. Since the chemical primary form of P stored in TC. Low phytate corn concomposition of TC and LPC manure differs (Wienhold tains a mutant gene that results in grain containing simiand Miller, 2004), studies are needed to determine if these manure types differ in their effects on soil quality. Assessing management effects on soil quality is comUSDA-ARS, Soil and Water Conservation Research Unit, Lincoln, NE 68583. Contribution of USDA-ARS and Univ. of Nebraska-Linplicated by the often conflicting results exhibited by coln. Journal Ser. no. 14104. U.S. Department of Agriculture, Agriculindividual soil attributes (Andrews et al., 2002). Manture Research Service, Northern Plains Area, is an equal opportunity/ agement assessment is best done using a dynamic assessaffirmative action employer and all agency services are available withment so that temporal variation in attributes and trends out discrimination. Received 15 Mar. 2004. *Corresponding author ([email protected]). Abbreviations: Db, bulk density; EC, electrical conductivity; Gw, gravimetric water content; LPC, low phytate corn; PD, particle density; Published in Soil Sci. Soc. Am. J. 69:206–214 (2005). © Soil Science Society of America POM, particulate organic matter; SMAF, soil management assessment framework; TC, traditional corn; WFPS, water-filled pore space. 677 S. Segoe Rd., Madison, WI 53711 USA