Estimating light interception using the color attributes of digital images of cotton canopies

Crop growth and yield depend on canopy light interception （LI）. To identify a low-cost and relatively efficient index for measuring LI, several color attributes of red-green-blue （RGB）, hue-saturation-intensity （HSI）, hue-saturation-value （HSV） color models and the component values of color attributes in the RGB color model were investigated using digital images at six cotton plant population densities in 2012-2014. The results showed that the LI values followed downward quadratic curves after planting. The red （R）, green （G） and blue （B） values varied greatly over the years, in accordance with Cai＇s research demonstrating that the RGB model is affected by outside light. Quadratic curves were fit to these color attributes at six plant population densities. Additionally, linear regressions of LI on every color attribute revealed that the hue （H） values in HSI and HSV were significantly linearly correlated with LI with a determination coefficient （R2）〉0.89 and a root mean square error （RMSE）=0.05. Thus, the H values in the HSI and HSV models could be used to measure LI, and this hypothesis was validated. The H values are new indexes for quantitatively estimating the LI of heterogeneous crop cano- pies, which will provide a theoretical basis for optimizing the crop canopy structure. However, further research should be conducted in other crops and under other growing and environmental conditions to verify this finding.

The impact of plant density and spatial arrangement on light interception on cotton crop and seed cotton yield:an overview

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.

Genotypic variation in spatiotemporal distribution of canopy light interception in relation to yield formation in cotton

Background: Within-canopy interception of photosynthetically active radiation(PAR) impacts yield and other agronomic traits in cotton(Gossypium hirsutum L.). Field experiments were conducted to investigate the influence of 6 cotton varieties(they belong to 3 different plant types) on yield, yield distribution, light interception(LI), LI distribution and the relationship between yield formation and LI in Anyang, Henan, in 2014 and 2015.Result: The results showed that cotton cultivars with long branches(loose-type) intercepted more LI than did cultivars with short branches(compact-type), due to increased LI in the middle and upper canopy. Although loose-type varieties had greater LI, they did not yield significantly higher than compact-type varieties, due to decreased harvest index. Therefore, improving the harvest index by adjusting the source-to-sink relationship may further increase cotton yield for loose-type cotton. In addition, there was a positive relationship between reproductive organ biomass accumulation and canopy-accumulated LI, indicating that enhancing LI is important for yield improvement for each cultivar. Furthermore, yield distribution within the canopy was significantly linearly related to vertical LI distribution.Conclusion: Therefore, optimizing canopy structure of different plant type and subsequently optimizing LI distribution within the cotton canopy can effectively enhance the yield.

LIGHT INTERCEPTION AND USE EFFICIENCY DIFFER WITH MAIZE PLANT DENSITY IN MAIZE-PEANUT INTERCROPPING

Intercropping increases crop yields by optimizing light interception and/or use efficiency.Although intercropping combinations and metrics have been reported,the effects of plant density on light use are not well documented.Here,we examined the light interception and use efficiency in maize-peanut intercropping with different maize plant densities in two row configurations in semiarid dryland agriculture over a two-year period.The field experiment comprised four cropping systems,i.e.,monocropped maize,monocropped peanut,maize-peanut intercropping with two rows of maize and four rows of peanut,intercropping with four rows of maize and four rows of peanut,and three maize plant densities(3.0,4.5 and 6.0 plants m^(-1) row)in both monocropped and intercropping maize.The mean total light interception in intercropping across years and densities was 779 MJ·m^(-2),5.5%higher than in monocropped peanut(737 MJ·m^(-2))and 7.6%lower than in monocropped maize(843 MJ·m^(-2)).Increasing maize density increased light interception in monocropped maize but did not affect the total light interception in the intercrops.Across years the LUE of maize was 2.9 g·MJ–1 and was not affected by cropping system but increased with maize plant density.The LUE of peanut was enhanced in intercropping,especially in a wetter year.The yield advantage of maize-peanut intercropping resulted mainly from the LUE of peanut.These results will help to optimize agronomic management and system design and provide evidence for system level light use efficiency in intercropping.

Influence of plant architecture on maize physiology and yield in the Heilonggang River valley

The size and distribution of leaf area determine light interception in a crop canopy and influence overall photosynthesis and yield. Optimized plant architecture renders modern maize hybrids(Zea mays L.) more productive, owing to their tolerance of high plant densities. To determine physiological and yield response to maize plant architecture, a field experiment was conducted in 2010 and 2011. With the modern maize hybrid ZD958, three plant architectures, namely triangle, diamond and original plants, were included at two plant densities, 60,000 and 90,000 plants ha-1. Triangle and diamond plants were derived from the original plant by spraying the chemical regulator Jindele(active ingredients,ethephon, and cycocel) at different vegetative stages. To assess the effects of plant architecture, a light interception model was developed. Plant height, ear height, leaf size,and leaf orientation of the two regulated plant architectures were significantly reduced or altered compared with those of the original plants. On average across both plant densities and years, the original plants showed higher yield than the triangle and diamond plants,probably because of larger leaf area. The two-year mean grain yield of the original and diamond plants were almost the same at 90,000 plants ha-1(8714 vs. 8798 kg ha-1). The yield increase(up to 5%) of the diamonds plant at high plant densities was a result of increased kernel number per ear, which was likely a consequence of improved plant architecture in the top and middle canopy layers. The optimized light distribution within the canopy can delay leaf senescence, especially for triangle plants. The fraction of incident radiation simulated by the interception model successfully reflected plant architecture traits. Integration of canopy openness is expected to increase the simulation accuracy of the present model. Maize plant architecture with increased tolerance of high densities is probably dependent on the smaller but flatter leaves around the ear.

Heterogeneity Analysis of Cucumber Canopy in the Solar Greenhouse

Detailed analysis of canopy structural heterogeneity is an essential step in conducting parameters for a canopy structural model. This paper aims to analyze the structural heterogeneity of a cucumber （Cucumis sativus L.） canopy by means of analyzing leaf distribution in a greenhouse environment with natural sunlight and also to assess the effect of structural canopy heterogeneity on light interception and photosynthesis. Two experiments and four measurements were carried out in autumn 2011 and spring 2012. A static virtual three-dimensional （3D） canopy structure was reconstructed using a 3D digitizing method. The diurnal variation of photosynthesis rate was measured using CIRAS-2 photosynthesis system. The results showed that, leaf azimuth as tested with the Rayleigh-test was homogeneous at vine tip over stage but turned heterogeneous at fruit harvest stage. After eliminating the inlfuence of the environment on the azimuth using the von Mises-Fisher method, the angle between two successive leaves was 144°;at the same time, a rule for the azimuth distribution in the canopy was established, stating that the azimuth distribution in cucumber followed a law which was positive spin and anti-spin. Leaf elevation angle of south-oriented leaves was on average 13.8° higher than that of north-oriented leaves. The horizontal distribution of light interception and photosynthesis differed signiifcantly between differently oriented leaves. East-and west-oriented leaves exhibited the highest photosynthetic rate. In conclusion, detailed analysis of canopy structural heterogeneity in this study indicated that leaf azimuth and elevation angle were heterogeneous in cucumber canopy and they should be explicitly described as they have a great impact both on light distribution and photosynthesis.

Row Spacing in Relation to Competition for Limited Resources in Soybean (Glycine Max L. Merrill)

Growing soybeans in different row-spacings introduces competition. Competition begins when the immediate supply of a single necessary factor falls below the combined demands of all plants. This paper reviews the main competition factors of genotypes, light, water, nutrients and weed in responses to row spacings for the past four decades. It demonstrated that responses of soybean genotypes to row width differ among cultivars, which depend on seasonal rainfall and irrigation. Determinate types produce more yield in narrow-rows, and cultivars with lodging resistance should be adopted in narrow-spacings, but indeterminate soybean should also be used to optimize yields in certain system. Narrow-compared with wide-row soybean (Glycine max) cultivation increases light interception (LI) and dominant components for the increase come from LAI, light extinction coefficients and branch types. Water use efficiency (WUE) and evapotranspiration are not influenced by row spacing, but seed yield could be increased if irrigation is applied. Nutrient uptake is significantly affected by row spacing, seed yields and uptake of N, P, K in plants increases with decreasing row spacing, and the effects depend on the fertilizer levels. Other factors rather than row spacing affect nitrogen fixation. Weed density, peak time and periodicity of weed emergence are not affected by row spacing, but better complementary weed control by the herbicides at the used doses can be obtained in narrow spacing due to the reduced weed number and dry weight. More researches are required to investigate the physiological responses, nutrient and water uptake and translocation, light utilization at different layers of canopy and soil environment changes in different row-spacings.

Infestation of insect pests in tree-rice agroforestry system

The prevalence of insect pests was studied on rice BRI 1 （mukta） as understory crop grown in association with 11 years old selected tree species viz, Akashmoni. Jhau and Albida in the field laboratory of the Department of Agroforestry, Bangladesh Agricultural University （BAU）. Mymensingh during the period from July to December, 2003. Among the three species Albida and Jhau possessed the largest canopy and there light penetration rate were high. On the other hand. Akashmoni had the lowest canopy but it penetrated low amount of light. Albida-rice association showed the lowest infestation of major rice insects followed by Jhau-rice association, while Akashmoni-rice association showed the highest insect infestation. Light intensity in the control plot （absent of tree species） was maximum and it caused minimum severity of insects infestation as compared to other associations. From the result it appeared that light interception has the relationship with insect population in rice. Therefore, tree species having sparse canopy which allowed easy penetration of sunlight is suitable for tree-flee agroforestry system.

Asymmetric Ridge–Furrow and Film Cover Improves Plant Morphological Traits and Light Utilization in Rain-Fed Maize

Light is one of the most important natural resources for plant growth. Light interception （LI） and use efficiency （LUE） are often affected by the structure of canopy caused by growing pattern and agronomy managements. Agro-nomy practices, such as the ridge-furrow system and plastic film cover, might affect the leaf morphology and then light transmission within the canopy, thus change light extinction coefficient （k）, and LI and LUE. The objective of this study is to quantify LI and LUE in rain-fed maize （Zea Mays L.）, a major cropping system in Northeast China, under different combinations of ridge-furrow and film covering ratios. The tested ridge-furrow system （DRF： ＂double ridges and furrows＂） was asymmetric and alternated with wide ridge （0.70 m in width and 0.15 m in height）, narrow furrow （0.10 m）, narrow ridge （0.40 m in width and 0.20 m in height）, and narrow furrow （0.10 m）. Field ex-periments were conducted in 2013 and 2014 in Jilin Province, Northeast China. Four treatments were tested： no ridges and plastic film cover （control, NRF）, ridges without film cover （DRF0）, ridges with 58% film cover （DRF58）, and ridges with 100% film cover （DRFl00）. DRF0 significantly increased LI by 9% compared with NRF, while film cover showed a marginal improvement. Specific leaf area in DRF experiments with film cover was significantly lower than in NRF, and leaf angle was 16% higher than in NRF, resulting in a 4% reduction in k. LUE of maize was not increased by DRF0, but was significantly enhanced by covering film in other DRF experiments, especially by 22% in DRF100. The increase of LUE by film cover was due to a greater biomass production and a lower assimilation portioning to vegetative organs, which caused a higher harvest index. The results could help farmers to optimize maize managements, especially in the region with decreased solar radiation under climate change.

Oxygation Enhances Growth,Gas Exchange and Salt Tolerance of Vegetable Soybean and Cotton in a Saline Vertisol

Impacts of salinity become severe when the soil is deficient in oxygen. OxygaUon （using aerated water for subsurface drip irrigation of crop） could minimize the impact of salinity on plants under oxygen-limiting soil environments. Pot experiments were conducted to evaluate the effects of oxygation （12% air volume/volume of water） on vegetable soybean （moderately salt tolerant） and cotton （salt tolerant） in a salinized vertisol at 2, 8, 14, 20 dS/m ECe. In vegetable soybean, oxygation increased above ground biomass yield and water use efficiency （WUE） by 13% and 22%, respectively, compared with the control. Higher yield with oxygation was accompanied by greater plant height and stem diameter and reduced specific leaf area and leaf Na^＋ and CI^- concentrations. In cotton, oxygation increased lint yield and WUE by 18% and 16%, respectively, compared with the control, and was accompanied by greater canopy light interception, plant height and stem diameter. Oxygation also led to a greater rate of photosynthesis, higher relative water content in the leaf, reduced crop water stress index and lower leaf water potential. It did not, however, affect leaf Na^＋ or CI^- concentration. Oxygation invariably increased, whereas salinity reduced the K^＋： Na^＋ ratio in the leaves of both species. Oxygation improved yield and WUE performance of salt tolerant and moderately tolerant crops under saline soil environments, and this may have a significant impact for irrigated agriculture where saline soils pose constraints to crop production.