The Impact of Plant Density and Spatial Arrangement on Light Interception on Cotton Crop and Seed Cotton Yield: an Overview
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CHAPEPA et al. Journal of Cotton Research (2020) 3:18 Journal of Cotton Research https://doi.org/10.1186/s42397-020-00059-z REVIEW Open Access The impact of plant density and spatial arrangement on light interception on cotton crop and seed cotton yield: an overview CHAPEPA Blessing1*, MUDADA Nhamo2 and MAPURANGA Rangarirai3 Abstract Light attenuation within a row of crops such as cotton is influenced by canopy architecture, which is defined by size, shape and orientation of shoot components. Level of light interception causes an array of morpho-anatomical, physiological and biochemical changes. Physiological determinants of growth include light interception, light use efficiency, dry matter accumulation, duration of growth and dry matter partitioning. Maximum light utilization in cotton production can be attained by adopting cultural practices that yields optimum plant populations as they affect canopy arrangement by modifying the plant canopy components. This paper highlights the extent to which spatial arrangement and density affect light interception in cotton crops. The cotton crop branches tend to grow into the inter-row space to avoid shade. The modification of canopy components suggests a shade avoidance and competition for light. Maximum leaf area index is obtained especially at flowering stage with higher populations which depicts better yields in cotton production. Keywords: Light interception, Plant populations, Spatial arrangement, Canopy architecture Introduction Bai et al. (2016), the extent and pattern of attenuation Plants contain the green pigment chlorophyll and they are determined by the architecture of the canopy and require light energy from the sun to photosynthesize cotton with columnar-type canopies exhibits an open and to grow. Light attenuation is an important aspect structure and it tends to grow into the inter-row that influences the overall photosynthetic rate and the space which allows it to intercept more irradiance accumulation of biomass of plants, particularly cotton moving down the crop canopy. This has a bearing on (Gossypium hirsutum L.). Thus light quality and light the flux density which is dependent on the orienta- duration play an important role in the productivity of tion of leaves within the canopy, the rate of photo- cotton. Cotton is a kind of sun-loving crop that requires synthesis will be below its maximum value if the flux many cloudless days to accumulate maximum biomass density is below the saturation level. which translates to high productivity. The crop normally Light which occurs in the form of the wavelengths of has regular shaped leaves (except for the okra leaf var- electromagnetic radiation, is visible to the human eye ieties) that are diaheliotropic (Sassenrath-Cole 1995; in the range of approximately 380–770 nm and plants Zhang et al. 2009). According to Turitzin (1978)and use the light in the wavelength of 400–700 nm for photosynthesis which is referred to as photosynthetic- ally active radiation (PAR). Interception of solar irradi- * Correspondence: [email protected] 1Department of Research and Specialist Services, Cotton Research Institute, P. ance by a crop canopy is a function of leaf area Bag 765, Kadoma, Zimbabwe index (LAI), absorption, reflection, and transmission Full list of author information is available at the end of the article © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. CHAPEPA et al. Journal of Cotton Research (2020) 3:18 Page 2 of 6 spectra of the component leaves and arrangement of canopy which may increase crop yields were suggested. leaves in the crop canopy (Campillo et al. 2012). Ab- These are cultural practices that yield optimum plant sorption of the light is one of the major determinants populations which affect canopy arrangement by modify- of crop yields apart from other factors like nutrient use ing the plant canopy components so as to ensure max- efficiency, water use efficiency and crop duration. The imum light attenuation into the plant canopy. Selection deterioration of light environment in the lower part of of varieties with a good geometry and leaf structure is the canopy due to heavy upper canopy foliage and small important, because it determines the behaviour of the leaf area of the subtending leaves, has been associated cotton plants in different spatial arrangements as influ- with low source-to-sink interaction of assimilates which enced by plant spacing adopted by the farmers. limits yield of lower bolls (Kerby et al. 1993;Niinemets 2007, 2016). Levels of PAR in high density plant popu- Canopy architecture and light interception lations of cotton have been shown to be low in lower The spatial distribution of photosynthetic organs within parts of the canopy due to decreasing ratio of red: far- a plant is referred to the canopy architecture and it red light provides energy for photosynthesis whilst varies greatly from species to species (Barthélémy and lower population densities also resulted in lower light Caraglio 2007). This has a significant bearing on the interception as most of the light was lost to the ground ability of light to enter the canopy and influence on the and thus resulted in lower productivity (Guinn 1974, as rate of photosynthesis (Song et al. 2013). According to cited by Constable 1994). According to Gwiranenzara Lieffers et al. (1999), the availability of light within a et al. (2014), a spacing of 0.7 m × 0.2 m gave a higher plant canopy differs from about 20 to 50 fold from top seed cotton yield compared with wider spacing of 1 to bottom within a closed canopy. This is due to a num- m × 0.3 m suggesting full light utilization due to better ber of different factors like leaf orientation, shape, spatial light interception. arrangement, sun elevation, and changes in spectral dis- The leaf orientation substantially affects penetration of tribution of the photosynthetic photon flux density light into the plant canopies. Horizontal leaves will cause (PPFD) within the plant canopy (Nobel et al. 1993; a decrease in irradiance whilst vertical leaves allow dee- Murchie and Reynolds 2013). In a crop like cotton, there per penetration of light into the canopy, thus determin- are two major types of canopies, the open canopy and ing the net canopy photosynthesis. Song et al. (2013) closed canopy (Reta-Sánchez and Fowlerb 2002). These suggested that the exponential extinction of light down canopies are directly linked to the leaf shape and struc- the canopy below a given leaf area index is a function of ture; the mutant deeply divided okra shaped leaf allows the transmission coefficient of the leaf taking into ac- for an open structure and a weakly divided or normal count the light reflected down into the canopy by leaf leaf type provides a closed structure for the plants. surfaces, their absorptive, transmittance and reflectivity These two different canopies affect the interception of capabilities. With an ideal leaf arrangement, twice as light differently and influence the overall yield. The use much leaf area is required to intercept all incident light of okra-leaf or sub-okra-leaf allowed competitive or with a leaf angle of 60 degrees than if the leaf with angle higher yields compared with normal leaf types to be ob- of zero degree. In general terms, if leaf area index is con- tained (Meredith 1984; Wells et al. 1986). According to stant, then the canopy interception will decrease as the Gonias et al. (2011), values of radiation use efficiency − leaf angle increases. Plant spaces affect the spectral dis- were estimated at 1.897 and 2.636 g•MJ 1 of intercepted tribution of the transmitted irradiance. For instance, in photosynthetically active radiation for the normal- and maize (Kasperbauer and Karlen 1994), the proportion of okra-leaf types, respectively. This clearly indicated the photons in PAR is less, and the photons of near infrared importance of canopies that allow solar radiation pene- are more in closely spaced plants than in widely spaced tration. Development of lower cotton bolls depends pri- plants. According to Dauzat et al. (2008), cotton showed marily on adjacent leaves (Kerby et al. 1980) and a marked plasticity under various densities which affects openness of the leaves, which permit light penetration to light quality moving down the canopy. lower leaves. The okra-shaped leaf varieties allow more Following evidence shows that photosynthesis is the interception of light by the lower leaves (Zhu et al. major limiting factor in yield of cotton. Even when the 2008). The early closure of rows and excessive vegetative plants are grown under maximum growing conditions, growth above developing fruiting branches usually cause considerable efforts have been done on ways to improve less penetration of sunlight into the canopy and, conse- the efficiency of the canopy for light interception and quently, cause an increase in the abscission of fruiting gaseous exchange (Guinn et al. 1976, as cited by Con- forms and a decrease in fibre quality (Kerby and Ruppe- stable 1994; Morales et al. 2020). The management and nicker 1992; Kerby et al.