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Rototillage, Disking, and Subsequent Irrigation

Effects on Soil Nitrogen Dynamics, Microbial Biomass, and Carbon Dioxide Efflux

Francisco J. Calderón^,* and Louise E. Jackson

Department of Vegetable Crops, Univ. of California, One Shields Avenue, Davis, CA 95616

View larger version (23K): [in a new window]   Fig. 1. Mean gravimetric moisture content of the rototilled, disked, and control soils in the main experiment. The soils were tilled at 0 h. The time of irrigation (222 h) is indicated by the vertical dashed line. For reference, 110 g H2O kg-1 is equivalent to -50 kPa. The error bars are the standard error of the mean (n = 3).

View larger version (33K): [in a new window]   Fig. 2. Mean values for the nitrogen pools of the rototilled, disked, and control soils. (a) NH4–N, (b) NO3–N, (c) dissolved organic nitrogen (DON), and (d) microbial biomass nitrogen (MBN). The soils were tilled at 0 h. The time of irrigation (222 h) is indicated by the vertical dashed line. The error bars are the standard error of the mean (n = 3). There were no significant differences in MBN at any time.

View larger version (35K): [in a new window]   Fig. 3. Mean values for the microbial biomass carbon, respiration, and CO2 efflux of the rototilled, disked, and control soils. (a) Microbial biomass carbon (MBC), (b) respiration, and (c) CO2 efflux. The soils were tilled at 0 h. The time of irrigation (222 h) is indicated by the vertical dashed line. The error bars are the standard error of the mean (n = 3). The least significant difference (LSD) between the treatments is shown. There were no significant differences in MBC or respiration at any point during the experiment.

View larger version (32K): [in a new window]   Fig. 4. Mean gravimetric moisture content, respiration, and CO2 efflux of the rototilled, disked, and control soils in the ancillary experiment. (a) Gravimetric moisture, (b) respiration, and (c) CO2 efflux. The soils were irrigated at 0 h. The error bars are the standard error of the mean (n = 3). Different letters indicate significant differences (P < 0.05) using t tests between treatments at each time. No t tests were done for the moisture data since only one replicate per treatment combination was analyzed.