IMPACT OF TILLAGE AND RESIDUE MANAGEMENT ON SOIL HEAT-FLUX

The quantity and percent cover of a crop residue in no-tillage (NT) af fects the transmission of radiation through the residue layer and alte rs soil heat flux compared with conventional moldboard tillage (CT). I t has been shown that NT results in cold soil temperature and reduced germination. A residue-free strip over the center of planting row can improve the thermal regime of NT but, limited information has been pub lished on the potential changes in heat flux density in no-tillage soi l with different residue management practices. Therefore, we conducted a study on simulated NT plots (with no crop) in 1986 and 1987 to eval uate the impact of tillage and residue-free strips in NT practices on heat flux density of soil-residue systems on Piano silt loam soil. The treatments were NT with a 0.31 kg m(-2) residue areal density with 5 (NT5), 15 (NT15), and 30 cm (NT30) wide residue-free strips. These tre atments were compared with 0.61 kg m(-2) residue areal density with 15 (NT15') and 30 cm (NT30') wide residue-free strips. A second large fi eld-scale (including crop) experiment was conducted in 1987 and 1988, where the NT30 and NT5 were compared with CT. Heat fluxes for soil and soil residue systems were measured or calculated from 1986 to 1988. I n the simulated NT study, soil surface heat flux (G(s)) in the center of the residue-free strip and conductive (G(mr)), and convective (G(ma )) heat flux at 15 cm away from the center of the residue-free strip a cross the residue layer were significantly greater in the NT30 than in the other treatments. Increases in G(s), G(mr) and G(ma) of NT30 comp ared with NT5, NT15' and NT15 were associated with increased temperatu re in-the-row and between-the-row at the soil surface and 5 cm depth. In the large field-scale study, the G(s) was within the range of - 123 .1 to 313.4 W m(-2) in CT, - 101.3 to 247.1 W m(-2) in NT30 and -69.8 to 209.1 W m(-2) in NT5 for 0-5 cm soil layer during 8-21 May 1987 and 1988. The G,, values at 15 cm away from the row center were significa ntly greater in treatments with 0.31 kg m(-2) residue areal density th an in treatments with 0.62 kg m(-2) residue areal density. The G(ma) i n NT30 and NT30' were significantly greater than in NT15, NT15' and NT 5. The 15 and 30 cm residue-free strips in NT30, NT30', NT15 and NT15' displayed greater heat input into the soil surface than the NT5 syste m. There was more heat input into the soil surface in no-tillage soil with residue-free strips in the spring which conserves soil and water because of a layer of the residue maintained between-the-rows. These m odified residue management systems could prove beneficial for early sp ring plant germination in cold regions. (C) 1997 Elsevier Science B.V.