| abstract: | Young "Ruby Red" grapefruit trees on sour orange (SO), Carrizo citrange (CA), Cleopatra mandarin (CL), or Swingle citrumelo (SW) rootstocks were used in a randomized split plot field experiment with 4 replications. Irrigation water has electrical conductivities of 0.7, 2.3, 3.9, or 5.5 dS m?1 (500, 1600, 2700, or 3800 ppm TDS). Three fertilizer applications included: fertigating weekly with first-year totals of 0.34 lb N tree?1 (L-34) or 0.23 lb B tree?1 (L-23), and broadcasting granular fertilizer at 6-week intervals with a total application of 0.54 lb N tree?1 yr?1 (D-54). Tree measurements taken in June and December showed reductions in canopy volumes of about 7% for each 1.0 dS m?1 increase in irrigation water salinity level above the base level of 0.7 dS m?1 (about 10% reduction for each 1000 ppm above 500). Trees on all rootstocks had either excessive leaf Na or CI accumulations at the highest salinity levels. Trees on CL were able to exclude CI better than the other rootstocks. Trees on Carrizo accumulated high levels of CI, but they were the most effective at excluding NA. Trees on CL had the greatest growth and those on SO had the least. Growth of trees on SW was slightly more than trees on CA, but both grew about 15-20% less than trees on CL. The L-34 fertigation proved superior to the other fertilization methods for all growth measurements. Growth was greater for the L-34 treatment even though the total seasonal N application rate was only about 60% of the broadcast fertilizer (D-54) rate. This advantage was apparent in all rootstocks at all salinity levels. |
