Forage growth and yield components as influenced by subsurface compaction

Subsurface soil compaction is a global problem that causes reduced plant gr owth and yield. The objective of this study was to evaluate responses of va rious growth and yield components of smooth bromegrass (Bromis inermis L. c v. Magna) and alfalfa (Medicago sativa L. cv. Rambler) to subsurface compac tion of sandy loam and clay Loam soils. Regression analysis indicated that all growth variables measured (shoot biomass, root biomass, number of alfal fa branches, number of smooth bromegrass tillers per plant, and leaf blade or leaflet width and length) had a negative relationship with soil bulk den sity in a Linear nature. However, these growth responses varied in their se nsitivity to subsurface compaction. For alfalfa, the most sensitive variabl e was the number of tertiary branches; for smooth bromegrass, shoot biomass was most sensitive. Leaf blade or leaflet length was the least sensitive v ariable to subsurface compaction. The study is unique in that it provides r esponse curves for various plant growth responses, an assessment of the sen sitivity of these parameters to subsurface compaction, and a data base for modeling these relationships. This study also provides plant-based indicato rs that should be related to soil-based indicators of compaction problems s uch as bulk density and soil strength, which are often used to determine th e extent of compaction.