Temporal Changes of Soil Water in Sandy Soils Amended with Pine Bark and Efficient Blueberry Irrigation

Abstract

Core Ideas Hydraulic properties of soil mixed with pine bark changed rapidly as bark degraded. Soil ρb increased from 0.33 to 0.62 g cm–3 and θfc increased from 7 to 21% in 2 yr. After 2 yr, no change in θfc indicated a constant capillary size porosity in the bark–soil mixture. Root zone depth in the bark–soil mix decreased continually to reduce plant‐available water. Sensors help monitor soil‐water dynamics that mimic the above changes in bark–soil mixtures. Temporal changes in the physical and hydraulic properties of pine bark as it degrades above sandy soil likely affect soil water (θv) availability and the efficiency of irrigation in blueberry (Vaccinium corymbosum L.) production. The objectives of this study were to (i) assess the physical and hydraulic properties of commercially available pine bark with large, medium, and fine grades as it aged above well‐ and poorly‐drained sandy soils, and (ii) test the capability of dielectric soil moisture sensors to monitor θv reliably through time. During 3 yr, the depth of the pine bark layer decreased from 26 to 15 cm, and the bulk density of the 0‐ to 15‐cm layer of pine bark increased from 0.33 to 0.62 g cm–3. The water content at field capacity (θfc) of pure pine bark was initially 0.07 cm3 cm–3 and increased to 0.21 cm3 cm–3 during the first 2 yr, but changed little afterward. The measured θfc at two sites with 2‐yr‐old pine bark remained between 0.19 and 0.21 cm3 cm–3 and agreed well with sensor estimates. The θfc gradually decreased with depth from 0.25 cm3 cm–3 at 7.5‐cm depth in the pine bark layer to 0.10 cm3 cm–3 at 60‐cm depth. The layer of pine bark mixed with well‐drained sandy soil reached the lowest θv (θl of 0.10 cm3 cm–3) after 12 d of drying, but this decrease in moisture required 40 d in poorly‐drained sandy soil. The root zone of pine bark in well‐drained sandy soil drained to θfc in <2 h compared with 3 h in poorly‐drained sandy soil. These data could be used to optimize irrigation efficiency.