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Abstract
Optimization of the plant population is one of the most important aspect for better growth and development of the crops. Optimum population of the plants is required to utilize all the growth factors viz. nutrients, water, light and space. If space is not properly utilized then there can be the more weed infestation which highly affects the crop production. Weeds contribute 45% loss in the overall yield of the crops among all the crop pests. Population of the plants also should not be maintained so high that all the moisture is drained out from the soil before crop reaches to the maturity. Hence population of the plants should be maintained in the unit area in such a way that each of the plant get all the essential inputs in very efficient way for their good growth. So proper planting geometry must be selected to efficiently utilize all the available space and growth factors.
Introduction
Plant population is defined as the total number of plants which are present at the given unit area of the land. Optimum population of the plant in the given area is very important for the healthy yield of the crops because plant population is directly responsible for the crop yield which depends upon the number of viable seeds, rate of survival and seed germination percentage. The population of the plants should be maintained in the unit area in such a way that each of the plant get all the essential inputs in very efficient way for their good growth.
In soil if the soil moisture and nutrients present in the sufficient amount then we can increase plant population for higher yield but under this condition solar radiation can be the limiting factor. Population of the plants in the field such that there is maximum interception of the solar radiation. So, when we have to decide about the plant population then each and every aspect which has potential to affect the crop yield should be taken under consideration. If the population of plants in field is high then there are some changes in the crop growth. There is increase in the plant height due to the competition of the light. High plant population also affects the thickness of the leaves. High plant population can increase the yield per unit area but individual plant yield is decreased. In case of determinate plants yield is decrease due to small ear size and in case of indeterminate plants yield is decrease due to reduction in number of ears.
Yield of individual plant and community
Crop spacing plays very important role for the better growth and development of the plant. Wider spacing of the crop provide all the favorable conditions to plant to show its full yield potential but when sown closer to each other then there is more competition between the plants for growth factors which results in the reduction in the yield and size of the plant. When we increase the population of the plants per unit area then yield/plant is decreased but there is increase in the yield/area due to efficient utilization of the growth factors. When we provide severe competition to individual plants, highest yield/area can be achieved.
Plant population and yield
Because of the higher plant density in case of indeterminate plants yield is decrease of the individual plant due to reduction in number of ears. In determinate plants yield is decrease due to reduction in the size of ears. The yield reduction can be optimized by selecting the crops having high tillering capacity of effective tillers.
Plants which have high branches and tillers behave as indeterminate plant and reduction in the yield due to reduction in the seeds number. With the plant population of 3.33 lakh/ha in redgram produces 20 pods/plants while at 50000 plants/ha produces about 100 pods/ha.
Plants which are non tillering and nonbranching results in low yield because of reduction in ear size in maize and sorghum.
Holliday (1960), a scientist gives two types of response curve to shows the relationship between plant population and yield which as follows:
- Asymptotic response
- IParabolic response
Asymptotic response
This response curve can be shown in the tobacco and fodder crops where whole plant contributes as the economic product. With increase in the plants density in wide spacing, there is increase in the dry matter of the individual plants because there is low competition between the plants. There is further increase in density of plants which also increase the plants dry matter but at a decreasing rate. After that increase in the plant population results in a plateau in which there is no increase in dry matter per unit area. The plateau continues for large increase in plant population. Therefore, for obtaining high yield, fodder crops are recommended under higher plant population.
Parabolic response
Parabolic curve shows the relationship between plant population and yield in those crops in which economic yield is the part of the total dry matter yield. In this case there is also increase in the population gives higher yield and then reaches maximum. But further increase in the population decreases the yield.
Optimum plant population
Optimum population of the plant is very important for getting higher yield per unit area. Optimum plant population based upon the following aspects:
- Size of the plant
- Elasticity of the plant
- Soil cover
- Dry matter partitioning
Size of the plant
Spacing of a particular crop affects the optimization of plant population. At the time of sowing of crop, we have to consider the spread and volume which is occupied by the individual plant at flowering time and according to which we have to decide the spacing.
For example: Wheat, rice and sorghum cover lesser space in the field as compare to redgram, cotton and sugarcane plant. There is also difference in the growing nature of the different varieties of the same crop. LRG-30 is the variety of redgram having 1.5-2 m height with 1-1.5 m spreading nature. There is another redgram variety that is ICPL 87 having 70 cm height and 30 cm spreading nature.
Elasticity of the plant
Variation in the size of plant between the minimum size of the plant that can produce some economic yield to the maximum size the plant can reach under unlimited space and resources is the elasticity of the plant. The variety of red gram ie. LRG 30 when reaches to the size of 20 g dry weight produces the few pods but it has potential to attain the size of 2000 g dry weight per plant and produces more pods.
In case of indeterminate and long duration crops elasticity of growth and yield characters of plants are high and range of optimum plant population is also high. For eg. Indeterminate redgram variety.
While in determinate plants, optimum plant population and elasticity in growth is less as in maize and sorghum.
Soil cover
For the maximum interception of the light the soil must be covered with crop as early as possible. The total dry matter production is directly proportional to the total interception of the light. Soybean crop which is closely spaced attained 95% light interception within 54-55 days gave 26-32% higher yield as compared to wider spaced crop.
Dry matter partitioning
Dry matter partitioning is the flow of assimilates from the source to sink organs. Translocation of the assimilates may depends upon the transport path which can be affected by the biotic and abiotic factors. Total dry matter production is related to the interception of light by the crop canopy. During the early stages of the crop more light is intercepted and more dry matter is produced.
Optimum plant population and environment
Environmental conditions play very important role for growth and development of the crops. Optimum plant population is different for different crops and also varies according to the environment under which a particular crop is grown.
Time of sowing
There are different weather conditions for the crop when sown at different periods. Optimum plant population highly depends upon the temperature and day length. There are some photosensitive varieties which requires light for flowering initiation. Under this condition day length play very major role for changing the size of the plant.
For example: Red gram which is sown in monsoon season occupies optimum plant population of 55000 plants/ha and this population is increased up to 3.33 lakh plants/ha when sown in winter season.
Irrigation
Irrigation is one of the most important factor for the optimum plant population and growth of the crops. Population of the plants is less when sown under rainfed conditions as compare to areas where irrigation facility is available.
Under irrigated and rainfed conditions water is lost from the crops and soil through the process of evapotranspiration (ET). When there is higher plant population in the field, water is lost more through the transpiration as compare to evaporation because soil is fully covered with the crop canopy. Higher plant population is recommended when there is availability of the irrigation water and adequate rainfall is occurred.
Fertilizer application
Optimum plant population or dense population is required to utilize all the nutrients which are present in the soil for obtaining higher yield. There is development of nutrient deficiency in the soil if large amount of plant population present in the field. For example: Without N application rice does not respond to optimum plant population. When we apply moderate amount of nitrogen ie. 50 kg/ha in rice field then higher population of plant gives more yield than lower plant population. By the application of higher amount of nitrogen ie. 100 kg/ha in field gives good results even under low plant population because of its good tillering nature.
Planting Pattern
Proper planting pattern is very important for the growth and development of the crops which has direct effect on the interception of the light, rooting behavior of the crop, moisture extraction pattern by the plant and proper management of the weeds to avoid competition.
There is difference between the crop geometry and plant geometry. Plant geometry refers to the shape of the individual plant and crop geometry is the shape of the space present for the individual plant. There are different types of planting system which are following:
Square planting
It is most commonly used system of planting in which inter-row and intra-row distance is same. In this all the plants are at right angle to each other and forms a square. In the square planting system, there is proper utilization of the space, moisture, light and nutrients by each of the plant present in the field. For eg. In tobacco effective management of the weeds by adopting square planting.
Rectangular planting
In this system of planting inter-row distance is more than intra-row distance. When sowing of crops with seed drill thus attaining rectangularity. Rectangularity is maintained in those crops in which intercultivation is major practice. In this system number of plants are less as compare to square system of planting.
Diagonal or Quincunx system
In this planting is done same as square system of planting, here only extra plant is adjusted at the center of the square only to utilize the extra space and increasing the yield. This system also helps to reduce the weed infestation. But there is slight increase in the competition for light, nutrients, water and space.
Conclusion
For obtaining the higher yield and high productivity it is very important and major task to properly utilize the available space to avoid wastage of land and also efficiently utilize the available nutrients, water, space and light. Nowadays population of the country is increasing and there is fragmentation of the land. Urbanization and industrialization decrease the cultivable land for the crop production which feeds the nation. So there is need to properly utilize the area for crop production and fulfills the need of farmers and nation itself.
References
- Rana, S. S. & Rana, M. C. Modern Concepts in Crop Production . Department of Agronomy, College of Agriculture, CSKHPKV, Palampur.
- Anderson, Walter. Some relationship between plant population, yield components and grain yield of wheat in a Mediterranean Environment . University of Western Australia.
- https://www.agrihortieducation.com/2016/09/systems-of-planting.html
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