Irrigation scheduling of drip-irrigated vegetable crops grown in greenhouses using continuous soil moisture monitoring

Continuous monitoring of volumetric soil water content (VSWC) has considerable potential for irrigation management (IM). Dynamic protocols were developed for IM of drip-irrigated vegetable crops grown in greenhouse-covered soils using the EnviroSCAN system (ES). Melon, tomato and pepper were grown sequentially. Drip emitters and plants were paired at 50 cm spacing, with 6-20 cm separation between each emitter and plant, depending on species, and 1.5 m between drip-lines. The manufacturer's recommended protocols ("Sentek protocols") were applied to melon, using a single ES probe located 6 cm from the plant and 10 cm from the emitter (position 1), with four sensors at different depths to 40 cm. The upper VSWC limit was defined by vertical drainage at 40 cm depth, and the lower limit by reduced/slowed crop water uptake when irrigation was withheld. The imposition of water stress on the extremely fast-growing melon crop (the crop grew from 0.7 m to 3.7 m height, in 6 weeks) was considered potentially deleterious. Additionally, because of the rapid growth, a series of potentially deleterious water stresses would be required to re-define the lower limit. In tomato, the Sentek protocol for the upper limit was unsuitable in this soil. Compared to IM with manual tensiometers, soil matric potentials (10 cm depth, 8 a.m measurement before irrigation) were considerably and consistently higher, -7 to -12 kPa compared to -14 to -20 kPa. After 3.5 months from transplanting seedlings, cumulative irrigation was 179 and 123 mm, respectively, for the ES and tensiometer-managed treatments. The high bulk density of 1.8 g cm(-3) at 10-20 cm soil depth, arising from constant foot traffic on moist soil, presumably impeded vertical drainage and promoted horizontal water movement. In pepper, an additional ES probe was installed in an "edge of bulb" (EOB) position, located 25 cm from the emitter. The upper limit was defined by vertical drainage at 40 cm depth (position 1) or horizontal water movement (accumulation at 0-20 cm depth at EOB position), and the lower limit by uptake at 40 cm depth (position 1) or reductions at 0-20 cm depth at the EOB position Compared to a tensiometer-managed treatment, total irrigation volume applied, fruit production and soil matric potential (10 cm depth) were very similar. These protocols are suggested for this and similar drip-irrigated horticultural systems.