Plant Density and Factors Affecting the Plant Density

Plant Density

Optimum plant density is necessary to obtain maximum yield. Optimum plant density depends on size of the plant, elasticity, foraging area, nature of the plant, capacity to reach optimum leaf area at an early date and seed rate used. The factors affecting plant density are grouped into two as (a) genetic and (b) environment factors.

A. Genetic Factors (plant or internal factors)

(i) Size of plant – The volume occupied by the plant at the time of flowering decides the spacing of the crop. Plants of red gram, cotton, sugarcane etc., occupy larger volume of space in the field compared to rice, wheat, ragi, etc. Even the varieties of the same crop differ in size of plant.

(ii) Elasticity of the plant – Variation in size or plant between the minimum size of the plant that can produce some economic yield to the maximum size of the plant that can reach under unlimited space and resources is the elasticity of the plant. The optimum plant density range is high in indeterminate plants. For example, in indeterminate red gram varieties the optimum plant density ranges from 55 to 133 thousand plants/ha. The elasticity of plants is due to branching or tillering. For determinate plants like maize, sorghum etc., the elasticity is less and hence the optimum plant density range is small. The removal of auxiliary buds is done to get uniform and early maturity in castor.

(iii) Foraging area or soil cover – The crop should cover the soil as early as possible so as to intercept maximum sunlight. More interception of solar radiation leads to more dry matter production. Closely spaced plants intercept more radiation than widely spaced plants. Area of root spread also decides the density.

(iv) Dry matter partitioning – Dry matter production is related to the amount of solar radiation intercepted by the canopy, which depends on the plant density. As the plant density increases, the canopy expands more rapidly, more radiation is intercepted and more dry matter is produced.

B. Environmental Factors (management factors)

The primary management factor affecting the plant density of any crop varieties is the method of stand establishment/sowings like transplanting or broadcasting. For transplanting/direct drilling, the genetic factors are the deciding factors on the number of plants per unit area. For broadcasting, the factors are:

(i) Time of sowing – The crop is subjected to different weather conditions when sown at different periods. Among the weather factors, the most important factors that influence optimum plant density are day length and temperature. Photosensitive varieties respond to day length resulting in change in size of the plant. As low temperature retards the growth, higher density is established for quicker ground cover.

(ii) Rainfall/irrigation – Plant density has to be less under rainfed than irrigated conditions. Under higher plant densities, more water is lost through transpiration. Under adequate irrigation or under evenly distributed rainfall conditions, higher plant density is recommended.

(iii) Fertilizer application – Higher plant density is necessary to fully utilize higher level of nutrients in the soil to realize higher yield. Nutrient uptake increases with increase in plant density. Higher density under low fertility conditions leads to development of nutrient deficiency symptoms. For example, rice does not respond to plant density without nitrogen application.

(iv) Seed rate – Quantity of seed sown/unit area, viability and establishment rate decides the plant density.

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