Soil Temperature, Air Temperature, and Defoliation Effects on Growth and Nonstructural Carbohydrates of Kentucky Bluegrass1

Abstract

AbstractKentucky bluegrass (Poa pratensis L., is used for turf in many areas where soil and air temperatures are high for long periods. Using controlled temperature water baths and growth chambers, Kentucky bluegrass ‘Merion’ plants were grown at various soil and air temperatures and at three clipping heights to determine the interaction effects of temperature and defoliation on growth. Defoliation reduced dry weight of tops, number of innovations, root length and percent of nonstructural carbohydrates at all soil and air temperatures. Although a soil temperature of 18 C produced the most root and top growth in unclipped plants, this superiority was completely negated by defoliation.A soil temperature of 27 C resulted in reduced root growth compared to that at 18 C. Defoliation intensified the unfavorable effect of the high soil temperature.Nonstructural carbohydrate levels were lowest at the soil temperature (18 C), that produced the highest vegetative growth in unclipped plants. Differences in nonstructural carbohydrates among the soil temperature treatments were greatly reduced by defoliation.In the growth chambers where soil and air temperatures were in equilibrium results were in general consistant with those where soil temperatures were regulated separately by means of the water baths. Highest number of innovations was obtained at 10 C regardless of defoliation treatment. Highest dry matter production of tops was obtained at 21 C on unclipped plants while all plants became dormant at 32 C and made no measurable growth.