Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2007
Publication Date: 5/12/2008
Citation: Franzluebbers, A.J., Stuedemann, J.A. 2008. Early response of soil organic fractions to tillage and integrated crop-livestock production. Soil Science Society of America Journal. 72:613-625. Interpretive Summary: Integration of crops and livestock could provide economic benefits to producers by intensifying land use and improving resource efficiency, but how this management might affect soil organic matter and its characteristics is not known. Scientists at the USDA-Agricultural Research Service in Watkinsville Georgia conducted a 3-year field experiment, whereby annual crops were grown following termination of perennial pasture. Two tillage systems were tested: (1) moldboard plow initially to break sod and disking thereafter) and (2) no tillage with herbicide application only. Two cropping systems were tested: (1) sorghum and corn in summer with rye as winter cover crop and (2) winter wheat with pearl millet as summer cover crop. Two cover crop management strategies were tested: (1) cover crops grazed by cattle and (2) cover crops left unharvested to mulch the soil. Tillage system had the most dominating influence on soil organic matter and microbial properties. If not tilled, soil organic matter remained very high near the soil surface and remained equivalent to long-term pasture. With plowing, soil organic matter was uniformly distributed within the plow layer and eventually was reduced in content due to greater decomposition. Cattle grazing cover crops did not have any major negative influences on soil organic matter, and sometimes even had positive influences on soil organic matter due to faster cycling of cover crop biomass to the soil through manure. The quality of soil, as evidenced by soil organic matter properties, was greater with no tillage than with conventional tillage. Therefore, crop and cattle producers who adopt integrated crop-livestock systems are encouraged to utilize conservation tillage management techniques to help retain soil organic matter and build soil quality. This recommendation can be applicable to small- and medium-sized farms throughout the southeastern USA.
Technical Abstract: Tillage, cropping system, and cover cropping are important management variables that control the quantity, quality, and placement of organic matter inputs to soil. How soil organic matter and its different fractions respond to management has not been comprehensively studied in integrated crop-livestock systems. We conducted a 3-yr field experiment on a Typic Kanhapludult in Georgia, in which long-term pasture was terminated and converted to annual crops. Tillage systems were conventional (CT, moldboard plow initially and disking thereafter) and no tillage (NT). Cropping systems were summer grain / winter cover crop and winter grain / summer cover crop. Cover crops were either grazed by cattle or left unharvested. Total organic C was highly stratified with depth under NT and relatively uniformly distributed with depth under CT. All soil C and N fractions were greater under NT than under CT at a depth of 0-6 cm. Tillage system had the most dominating influence on all soil C and N fractions and cropping system the least. At the end of 3 yr, total organic C at a depth of 0-30 cm was lower under CT than under NT [42.6 vs. 47.4 Mg ha-1 (P < 0.001)]. Potential C mineralization was also lower under CT than under NT [1240 vs. 1371 kg ha-1 24 d-1 (P = 0.02)]. Grazing of cover crops by cattle had both positive and negative effects on soil C and N fractions within the surface 6 cm. To preserve high surface-soil C and N fractions and total plow-layer contents, NT cropping following termination of perennial pasture is recommended. In addition, since cattle grazing cover crops did not consistently influence soil C and N fractions, integrated crop-livestock systems are recommended as a viable conservation approach while intensifying agricultural land use.