Effects of severe defoliation on the morphological characteristics of grasses

3 months ago (Edited)

Defoliation, whether by grazing, cutting or natural factors, is a process that exerts a significant influence on the morphological characteristics of grasses, this removal of aerial biomass triggers a series of physiological and morphological responses in plants, with the aim of maintaining their survival and growth.

Main impacts that severe defoliation in pastures can cause

Root Growth: Severe defoliations of grasses can cause a greater reduction in radical growth than moderate defoliations, this is because the distribution of energy resources changes drastically after each severe defoliation, because after the removal of leaf area the photosynthetic activity decreases and the reserves used for root growth are sent are diverted for the growth of the leaf area.

Reduction of leaf area: Defoliation decreases the leaf area, which in turn reduces the photosynthetic capacity of the plant. This directly affects the production of biomass and the accumulation of reserves.
Alteration of vegetative growth: Plants respond to defoliation by activating their meristems (growth zones) to produce new leaves and stems. However, the intensity and frequency of defoliation can affect the growth rate and the distribution of biomass between different parts of the plant. The plants that persist under intensive grazing are those that have the growth points close to the soil surface, which indicates that the cutting height is important to consider at the time of being grazed.
Stem dynamics: Defoliation can reduce or stimulate the production of stems in pastures attributed to different variables such as differences between species, phenological status of the plant, time and intensity of grazing. According to Clavero (1991), I reported that the stress of defoliation increases the proportion of dead stems decreases the ratio of Live/Dead stems, When the apical meristems of a stem are completely removed the stem does not produce new leaves and all new growth depends on a new stem, frequent and intense defoliations remove almost the entire leaf area and retards the production of stems through a reduction in photosynthetic activity.

Development of reserve structures: To cope with periods of stress, plants can increase the production of storage organs such as rhizomes and stolons, which allows them to survive adverse conditions and quickly regrow after defoliation.

Among the factors that influence the effects of defoliation are the intensity of the defoliation since, the amount of biomass removed directly influences the response of the plant, a severe defoliation can cause greater stress and negatively affect growth. Also the frequency of defoliation because, frequent defoliations can limit the ability of the plant to recover and accumulate reserves, which can lead to a decrease in production in the long term. Defoliation at different phenological stages may have different effects, for example, defoliation during the active growth phase may be less detrimental than during flowering or fruiting. Different species of grasses have different responses to defoliation due to their genetic and morphological characteristics.

In the same vein, understanding the effects of defoliation is fundamental for the sustainable management of pastures.Proper management can maximize forage production, improve nutritional quality and conserve species diversity. These are some of the strategies that can be established to make a more appropriate management: * Adjust the frequency and height of cutting: It is necessary to find a balance between the demand for fodder and the resilience of the plants.

Rotate grazing: Rotating the animals between different paddocks allows the plants to recover and prevents overgrazing.
Select adapted grass species: Choosing grass species tolerant to defoliation and with high regrowth capacity is essential to maintain the productivity of grasslands.

Final considerations

Dear readers, in summary, defoliation is a key factor that shapes the morphology and physiology of pastures, by understanding the underlying mechanisms and their implications, producers can make informed decisions to optimize the management of their pastures and ensure long-term sustainable production. According to Clavero (1991), in tropical tufted grasses, the maximum yield of living material, root weight, number of stems, live/dead stem ratio, light interception, leaf area index occur with adequate fertilizations and less frequent and severe defoliations. The weight of the root crown is related to the number of stems, diameter of tillers, and dry matter production. . In general, the highest dry matter yields and growth rate are obtained with fertilization and defoliation practices that allow the greatest use of incident light throughout the growth period, reducing the need to use reserve carbohydrates as an energy source for regrowth.

Bibliographic references

Clavero, T. (1991). Course on production and research in tropical grass. Editorial Agropecuaria "Circulo ganadero de venezuela" Maracaibo: Venezuela.

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