Soil Compaction and Moisture Stress Preconditioning in Kentucky Bluegrass. I. Soil Aeration, Water Use, and Root Responses1

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Abstract
Soil compaction and moisture stress are major problems on recreational turfgrass sites. In the greenhouse, we investigated root responses to soil compaction and moisture stress preconditioning, and their effects on water use of Kentucky bluegrass (Poa pratensisL. ‘Ram I’). The compaction treatments included: (i) NC = no compaction, (ii) LT = long‐term compaction (equivalent to 720 J energy) over a 99‐day period, and (iii) ST = short‐term compaction for 9 days. Irrigation regimes were initiated at the same time as LT compaction. They included: (i) well watered = irrigation at −0.045 MPa and (ii) water stressed = irrigation at −0.400 MPa. Ninety‐nine days after initiation of preconditioning treatments and after watering each treatment to saturation, a dry‐down cycle was started. Compaction treatments reduced ODR to below 0.20 µg cm−2min−1for 143 h compared with 26 h in the uncompacted turf. Long‐term compaction increased root weights in the upper 5 cm and decreased root weights in the lower 10 to 20 cm profile. Short‐term compaction decreased root weights only at 15 to 20 cm. Root porosity was increased by LT compaction, but the greatest increase was for the combination of LT compaction and water stress resulting in root porosities of 23%. Plants with higher root porosities also exhibited greater water uptake during low soil O2conditions. Soil compaction reduced total water use and moisture extraction in the deeper zones. Moisture stress preconditioning had no effect on root distribution but resulted in greater total water use, primarily from the 0‐ to 5‐ and 5‐ to 10‐cm soil zones.