Black oat cover crop management effects on soil temperature and biological properties on a Mollisol in Texas, USA

Abstract

Management of a black oat ( Avena strigosa [Schreb.]) cover crop by mowing method (none, flail mowing, or sickle bar mowing) affected soil micro environmental conditions and soil microbial and chemical properties. Soil temperatures at depths of 0, 5, 10 and 20 cm were highest in flail mowed treatment plots (up to near 45 °C at 5 cm depth), followed by sickle bar mowed plots (averaging 10 °C lower at 5 cm depth). Lowest soil temperatures were maintained in plots that were not mowed; averaging 5 °C lower at 5 cm depth than the sickle bar mowed plots. Increasing temperature convergence was observed below 5 cm, with the highest temperature (flail mowed treatment) at 32 °C and the lowest (not mowed) at 27 °C. Microbial biomass increased significantly ( P < 0.05) from < 100 mg C kg − 1 soil in the late spring, to > 150 mg C kg − 1 in the early fall. β-glucosidase and alkaline phosphatase activities decreased slowly throughout the experiment, and were significantly greater ( P < 0.05) only when comparing the not mowed treatment to both mowing treatments. Dissolved organic C (DOC) decreased sharply, perhaps due to rainfall. Similarly, soil inorganic N decreased sharply, from approximately 0.025 mg N kg − 1 soil in the not mowed plots, to approximately 0.005 mg N kg − 1 during a rainy period. Immobilization of N during rapid microbial biomass growth could also explain the decrease in inorganic N. While resin-extractable P was significantly higher in the not mowed treatment, few differences in extractable P were detected between either mowing treatment during the experiment. Standing oat residues maintained higher levels of soil enzyme activities and the lowest microbial biomass, suggesting that controlling contact of crop residues with the soil may introduce a rate limiting factor for residue decomposition. The timing of residue decomposition in this system may be delayed by leaving most of the plant biomass above the ground (i.e. not mowed or sickle bar mowed). These residue management factors may be important in controlling soil nutrient transformations and soil organic matter maintenance in subtropical climates.