An Alberta Agriculture and Forestry (AF) specialist says it’s important to good pasture management to have a solid understanding of the different ways plants respond to dry conditions.
“Pasture plants rely on their root systems and the energy they store,” says Andrea Hanson, beef extension specialist, AF, Airdrie. “Plants with a deep root system or tap roots can reach further for that sub-surface moisture whereas plants with a more shallow or depleted root system are affected by dry conditions much sooner. If you’re in a dry area, you may have already seen how the alfalfa is further along than the grasses in the pastures and ditches.”
How plants in a pasture respond to dry conditions depends on how the pasture was managed in previous years.
“Producers who have carefully grazed their pastures prior to this dry spring have pasture plants with a healthy root system and, therefore, stored energy,” says Hanson. “A new pasture or one that has a continual or long history of good grazing management often has diverse plant species with more deep-rooted types. These plants are more able to access moisture deeper in the soil and avoid dry conditions until subsurface moisture is depleted. As a result, these pastures will take longer to show the signs of stress.”
About 50-80 per cent of a healthy plant’s mass is below ground in its root system. “However, a stressed plant’s root system is less than half of its entire biomass and, the lower it is, the more stressed it is. When a plant has a healthy and strong root system, it’s able to draw moisture from further down the soil profile and, if necessary, draw from its stored reserves. The more a plant has to draw from its reserves before being able to recover those reserves in its roots, the more stressed the plant becomes. A plant that is stressed losses root matter. This creates a counter-productive cycle being that results in the plant being much less able to cope with dry conditions. More time is needed for plants to recover from grazing when plant growth is slow. Days of overgrazing can delay regrowth by weeks, especially in dry conditions.”
Source : Agriculture and Forestry