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Short-Term Dynamics of Nitrogen, Microbial Activity, and Phospholipid Fatty Acids after Tillage

^a Edificio Julio Garcia Diaz 102, Departamento de Biologia, Universidad de Puerto Rico, PO Box 23360, San Juan, PR 00931-3360
^b Dep. of Vegetable Crops, Univ. of California, One Shields Avenue, Davis, CA 95616
^c Dep. of Land, Air and Water Resources, Univ. of California, One Shields Avenue, Davis, CA 95616

View larger version (16K): [in a new window]   Fig. 1. Mean gravimetric moisture content of the rototilled and control Pico silt loam soils. The error bars are the standard error of the mean . The dashed lines show the soil matric potential of the highest and lowest values

View larger version (21K): [in a new window]   Fig. 2. Mean values for the nitrogen pools and rates of nitrogen transformations of the rototilled and control Pico silt loam soils. (a) NO3-N, (b) nitrification potential, (c) MBN, and (d) denitrification rate with acetylene block. Day zero is the time of tillage. The sample at 0.04 d was obtained in the field immediately after tillage, while later samples were taken from intact cores incubated in the 20°C growth chamber. The error bars are the standard error of the mean. The Least Significant Difference (LSD) based on a Student's t-test between tilled and control soil is shown

View larger version (20K): [in a new window]   Fig. 3. Mean values for the carbon pools and rates of C transformations of the rototilled and control Pico silt loam soils. (a) respiration rate as measured by 1-h soil incubation, (b) MBC, (c) qCO2, and (d) CO2 efflux from the soil surface. The sample at 0.04 d was obtained in the field immediately after tillage, while later samples were taken from intact cores incubated in the 20°C growth chamber. The error bars are the standard error of the mean. The Least Significant Difference (LSD) based on a Student's t-test between tilled and control soil is shown

View larger version (12K): [in a new window]   Fig. 4. CCA ordination biplot of the PLFA profiles in the study of short-term tillage responses on the Pico soil. Tilled soil is designated t and the control soil is designated n. The number of days after tillage follows the t or n designation. Axis 1 has an eigenvalue of 31%, while Axis 2 has an eigenvalue of 25%

View larger version (15K): [in a new window]   Fig. 5. Mean total PLFA of the rototilled and control Pico silt loam soils. The error bars are the standard error of the mean. . The Least Significant Difference (LSD) based on a Student's t-test between tilled and control soil is shown