The influence of partial root volume irrigation on water relations and expansion of roots and leaves of papaya plants was determined using split root containers. In one study, `Tainung #1' and Solo #8 seedling roots were trained into four compartments until well-established, then water was withheld from 0, 1, 2, or 3 quadrants. Mid-morning stomatal conductance and predawn relative leaf water content were not affected by the irrigation treatments. Similarly, relative root water content in the dry quadrants was not different from that in the watered quadrants. In a second study, `Red Lady' seedling roots were trained into four compartments which contained a 13 × 13-cm plexiglass observation window. After the plants were well-established, watering was continued in one of 4 (1:4) or four of four (4:4) quadrants. Leaf midrib and root extension were measured at 06:00 and 18:00 hr each day. Daily growth of roots in the dry quadrants was reduced 25% below that in the watered quadrants, and midrib extension of the 1:4 plants was reduced ≈10% below that of the 4:4 plants. Irrigation treatments did not influence the percentage of growth occurring during the diurnal and nocturnal periods. The dry quadrants of 1:4 plants were almost devoid of fine roots. The number of root tips on the observation windows of the 1:4 plants was reduced 43% in the dry quadrants and increased 22% in the wet quadrant compared with that for the 4:4 plants.
Partial Root Volume Irrigation of Papaya Plants in Split Root Containers