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Soil Temperature, Nitrogen Concentration, and Residence Time Affect Nitrogen Uptake Efficiency in Citrus

^a Agronomy Dep., 304 Newell Hall, Univ. of Florida, Gainesville, FL 32611
^b Univ. of Florida, Citrus Res. and Educ. Center, 700 Experiment Station Road, Lake Alfred, FL 33850
^c Soil and Water Science Dep., Univ. of Florida, IFAS, Gainesville, FL 32611

View larger version (22K): [in a new window]   Fig. 1. (A) Average soil temperature at the 20-cm soil depth and relative humidity (RH) during uptake periods. (B) Average weekly evapotranspiration (ET) rates of reference columns planted with Swingle (SWL) and Volkamer (VLK) seedlings (error bars represent ± one SE from the mean, n = 2).

View larger version (24K): [in a new window]   Fig. 2. Nitrogen uptake (mg N per plant) as affected by residence time (t = 2, 4, or 8 h) for the 7 mg N L-1 treatment for Swingle (A) and Volkamer (B) seedlings (error bars represent ± one SE from the mean, n = 4).

View larger version (29K): [in a new window]   Fig. 3. Nitrogen uptake (mg N per plant) as affected by residence time (t = 2, 4, or 8 h) for the 70 mg N L-1 treatment with Swingle (A) and Volkamer (B) seedlings (error bars represent ± one SE from the mean, n = 4).

View larger version (25K): [in a new window]   Fig. 4. Incremental nitrogen uptake efficiency (NUE) (quadratic component of the regression equations listed in Table 2) as related to leaf area expansion between 2 Dec. and 31 May for Swingle (SWL) and Volkamer (VLK) seedlings with the 7 mg N L-1 (N7) and 70 mg N L-1 (N70) treatments.

View larger version (26K): [in a new window]   Fig. 5. Nitrogen uptake (mg N per plant) as related to evapotranspiration rates of reference plants for Swingle (SWL) and Volkamer (VLK) seedlings with the 7 mg N L-1 (A) and 70 mg N L-1 (B) treatments. Regression equations express nitrogen uptake for Swingle (NUS) and Volkamer (NUV) as a function of the evapotranspiration (ET) rates for reference plants.

View larger version (21K): [in a new window]   Fig. 6. Nitrogen uptake (mg N per plant) as related to the uptake temperature sum (UTS) during uptake for Swingle (SWL) and Volkamer (VLK) seedlings with the 7 mg N L-1 (A) and 70 mg N L-1 (B) treatments. Regression equations express N uptake as a function of UTS values expressed in °CdN (UTS values assume a base temperature for citrus of 10°C, with one °CdN unit being accrued by 2.4 h uptake at 20°C or 1.6 h uptake at 25°C).

View larger version (22K): [in a new window]   Fig. 7. Potential nitrogen leaching (PNL) index as a function of the uptake temperature sum (°CdN) for Swingle (SWL) and Volkamer (VLK) seedlings with the 7 mg N L-1 (A) and 70 mg N L-1 (B) treatments. Regression equations expresses PNL index as a function of uptake temperature sum (UTS) values.