SportsTurf provides current, practical and technical content on issues relevant to sports turf managers, including facilities managers. Most readers are athletic field managers from the professional level through parks and recreation, universities.
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FieldScience Continued from page 12 matures, it turns brown and becomes thin- ner. Its ability to absorb water and nutrients declines. Eventually the whole root will die and will slough off just below the crown. This cycle of root growth, maturity, senes- cence, death and replacement is a natural and ongoing process. Its rate can be dramati- cally influenced by the environment, climate, soil conditions or cultural practices. HOW DO TURFGRASS ROOTS GROW? Cool-season grasses. To understand the from CO2 and H2O. These carbohydrates, when broken down through the process of respiration, provide energy to the plant. Roots do not contain chlorophyll and so cannot photosynthesize. They depend on the shoot system for carbohydrates for their energy needs. The absorption of nutrients from the soil by the roots and the move- ment of water and nutrients from cell to cell within the root require energy. The roots of cool-season grasses grow cycle of cool-season grass root growth, con- sider the cycle of carbohydrate production and use. In photosynthesis, plants use the energy of sunlight to produce carbohydrates and function most vigorously when soil temperatures are cool. The most intense pe- riod of root initiation and growth is in the spring. A slightly less active period occurs in the fall. The temperatures for maximum root growth are slightly lower than those for maximum shoot growth, and so roots will be functioning and growing before shoot growth begins in the spring and as shoot growth slows and stops in the fall. Carbohy- drates are moved into stems and to a lesser extent into roots as late season growth winds down, providing for slow but contin- ued growth in cold (not frozen) soils until active growth resumes in spring. Cool-season grass shoot growth is most efficient at air temperatures of 60–75F while root growth is most efficient at soil temperatures of 55–65F. When air temperatures rise in summer, the efficiency of photosynthesis in cool-sea- son grasses is reduced. The leaves produce fewer carbohydrates. Energy available for root growth and work is reduced and as a result root growth slows. As root growth slows, the root system becomes limited in its ability to absorb water and nutrients from the soil and transmit them to the other parts of the plant. tures will follow. As soils warm, root respi- ration in cool season grasses increases. As respiration increases more carbohydrates are used up. So, when temperatures warm, the use of carbohydrates increases while the supply decreases. Eventually this can lead to root starvation and death. Roots will not be replaced, and the result will be a net loss of roots to sustain the rest of the turfgrass plant until cool weather resumes. Under drought conditions, some grasses As air temperatures rise, soil tempera- actively shift carbohydrates to the roots, particularly the roots which are in the lower, moister part of the rootzone. This shifting of carbohydrates can serve to sus- tain the root system where it can harvest water, and thus provide a direct benefit to the shoot system. Warm-season grasses. Photosynthesis is more efficient in warm-season grasses than in cool-season grasses. As temperature and light increase, so too do shoot and root growth. Root initiation and activity peak in late spring and summer. When tempera- tures cool down, root as well as shoot growth slows. When the plant enters dor- mancy, root growth ceases. The peak loss of roots for warm-season grasses occurs in winter, particularly late winter. Warm sea- son shoot growth is most efficient at air temperatures of 80–95F while root growth is most efficient at soil temperatures of 75– 85F. WHAT DO TURFGRASS ROOTS DO? Roots absorb water. Roots are the prin- cipal entryway for this essential compound. Water is needed to maintain turgor, for photosynthesis, for the transport of materi- als, and for many other processes in the plant. Water is needed to replace transpira- tional loss as well as that lost through mown leaf ends. Roots absorb nutrients. While carbon, >> EXCELLENT ESTABLISHMENT PRACTICES, proper watering and prudent fertility lead to the growth of deep roots, as seen in this sample from a seedling sports turf. hydrogen and oxygen, the main building blocks of organic compounds, are derived from the atmosphere and from water, the remaining essential mineral nutrients are principally absorbed from the soil by the roots. Nutrients do not just "seep into" or passively move into roots. The process of nutrient uptake and absorption requires en- 16 SportsTurf | May 2012 www.sportsturfonline.com