Effects of low light intensity on radiation use efficiency and productivity of tropical pulses

Pulses have distinct morpho-physiological response under reduced sunlight. But little is known for their capacity to adapt to the level of shading encountered in crop mixtures. Field experiment was conducted to evaluate the pulses under artificial shade during rainy season at Raichur, Karnataka. Objectives were to select potential pulse crop tolerant to shade based on productivity and radiation use efficiency (RUE). Experiment was laid out in split-plot design, wherein light intensity (unshade, 50 and 75% shade) in main plots and pigeon-pea, cowpea, lablab and black-gram were in sub plots. Shade levels were created by the erection of white shade nets at 25 DAS continued upto harvest. Results indicated that irrespective of the crop more pods, grain, stover and protein yield were recorded under unshade. While, pigeon-pea and lablab were produced significantly higher yield under unshade, however, these were also well performed under 50 per cent shade over black-gram and cowpea. However, seeds crude protein was higher in shaded plants compared to unshaded. Significantly higher RUE (2.22 gMJ -1 ) was recorded in pigeon-pea under 75 per cent shade and lowest in unshaded lablab (0.35 gMJ -1 ) and black-gram (0.40 g MJ -1 ). Results inferred that pigeon-pea and lablab were found tolerant to shade compared to cowpea and black-gram and may be suitable for crop mixtures cultivation.

environment is also critical to plant survival and efficiency in production. The photosynthetically active radiation (PAR) is major factor regulating photosynthesis and other physiological processes which are ultimately govern the dry matter production (Lemaire et al., 2007). In general, plants under high light intensity are known to reduce the photosynthetic rate under the shade. Selection of species that perform stable photosynthesis under various light intensities will be a greater advantage to achieve high and stable productivity in natural environments.
Farmers adopt intercropping primarily to increase their product diversity and farm income stability through the effective use of land and other resources.
Pulses are known for differential tolerance to reduced light in crop combinations. Selection of these pulses in association with other crops depends on their potential growth (Pang et al., 2017). Grain yield of pulses have been reported to reduce when intercropped with cereals and other crops. The low yield in species of intercropped pulses compared to monoculture is primarily due to shading that has led to poor development of plants. The decrease in light reaching the canopy of the legume when intercropped with other plants was about 30-50 per cent of the complete incoming radiation and started about 30-35 days after crop seeding (Armstrong et al., 2008). The choice of appropriate species of pulses plays a significant role in crop mixtures cultivation to achieve the maximum yield of intercropped pulses under low light intensity.
The species may respond to shading stress differently in terms of morpho-physiological characters as well as yield. Pulses are grown under a shade with minimum reduction in yield also perform better in intercropping systems (Fagwalawa and Yakasai, 2013;Reza, 2005).
Under tropical conditions, evaluation of different pulses based on shade tolerance capacity in turn suitability to the intercropping system was not properly documented. Therefore, the objectives of the present study were to test the performance of pulses grain yield to differed densities of shading, to explore responses of the morphological and physiological traits to shading and to reveal the relationship between yield performance and responses of the morphological traits under lower light shading. cv. DU-1 were assigned to sub-plots.

The experiment was conducted in
The crops were sown on 17 th July, 2014 and 21 st July, 2016 and raised as per the crop specific package of practices recommended for the region. In 2015, experiment was vitiated due to heavy rainfall that resulted poor establishment of pulses. At 25 DAS, artificial shade was created by aluminet shade cloth coverage and maintained upto maturity. Shading nets were erected in a rectangular frame at two-meter height above the ground to ensure good ventilation and were large enough to fully cover the corresponded shaded plots. There were two light levels  Table 1. Vol. 23, No. 3

Statistical analysis
The experimental data were subjected to statistical analysis adopting Fisher's method for analyses of variance as outlined by Gomez and Gomez (1984). The level of significance used in the 'F' test was given at 5%.
Least significant difference (LSD) values have been given in the Table 2 at 5% level of significance, wherever the F test was significant. and 125.7MJ m -2 ).

Canopy characters
Canopy characters were differed significantly during the crop growth period due to artificial shade levels and pulse species (  canopy.

Yield and yield attributes
Artificial shade had significant impact on grain yield of all the species selected for the study. Species grown under no shade have out yielded over reduced light  was accumulated in lablab (5566 kg ha -1 ) followed by pigeon-pea (4743 kg ha -1 ) and least in black-gram (1124 kg ha -1 ). This might be due to higher total dry matter  intensity. Bhagat et al. (2017) also opined that soybean genotypes were responded variedly to reduced PAR and irrigation.

Radiation use efficiency
Under field conditions the interception of the incoming PAR by leaves is a major process of biomass production. Grain yield-based radiation use effectiveness has a sign of canopy growth and the light interception and was considerably affected by artificial shade levels and pulses (Fig. 1) developed relationship and reported that between dry matter production, light interception and radiation use efficiency of different wheat varieties were higher correlated.

Grain quality
The grain crude protein content was significantly influenced by artificial shade levels ( This can be ascribed to greater manufacturing of biomass leading to greater yields of grain under no shade (Pang et al., 2017). The formidable correlation between grain yield and crude protein yield (0.97) is further evidence of this (Table 4). Protein output in pigeon-pea was considerably greater and the magnitude of increase was 40, 20, and 77 per cent, respectively, compared to cowpea, lablab, and black-gram. This was primarily due to greater pigeonpea grain yields over other plants (Olalekan and Bosede, 2010).

Relationship between yield and growth, yield attributes
The relationship between growth parameters, yield parameters, RUEg and protein yield were worked out (Table 4). Grain yield of pulses was significantly positively correlated with total dry matter at harvest (r=0.919) then light interception (r=0.752) and relative water content (r=0.6). Similarly, these parameters also significantly related with stover yield of pulses. However, Vol.

CONCLUSION
In the present study, pulses are susceptible to light under moderate shade condition, but the difference in yield and yield components can be noted. Pigeon-pea and lablab performed among the tested pulse species with minimal yield decrease and better shade tolerance compared to black-gram and cowpea. The shaded plants had higher RUE than the no shade and shading reduced the availability of radiant energy at the canopy surface. Therefore, these are potential pulses for intercropping with tall statured crops that offer a significant amount of shade.