Physiological Efficiency of Weeds in Rice Fallow Fields

Photosynthetic rate, Transpiration rate and Stomatal Conductance is measured in different weeds during July’2020 in rice fallows using IRGA- Photosynthesis system model Lci- T. We have chosen all the weeds at flowering to maturity phase and observed the data. Among the weeds analysed Parthenium hysterophorus has recorded very high Photosynthetic rate (µ molm-2 Sec-1)and there was difference with stage also, Flowering stage (165.28) has recorded a higher photosynthetic rate followed by vegetative (123.2) and maturity phase (118.72) and found that transpiration rate also followed the same trend. Even this has recorded more than the C4 crop photosynthetic rate for example Trianthema portulacastrum which has recorded a photosynthetic rate of 21.98, which was the next highest photosynthetic rate among the weeds recorded and as well as over C4 crops too. Among the grasses Paspalum sp., Echinochloa colona (7.81µ molm-2 Sec-1)) and Cynodon dactylon (4.2µ molm-2 Sec-1)) has recorded higher photosynthetic rate. Cyperus and Cyanodonhas recorded with lesser stomatal conductance and transpiration rate but has recorded higher photosynthetic rate which can thrive better in rainfeds also. Echinochloa has more transpiration rate and stomatal conductance among grasses and this might be due to their water loving nature. Boerhavia diffusa, Euphorbia hirta and Ruella tuberosa are recorded with lesser stomatal conductance. On critically analysing the weeds, it was observed that some weeds like Parthenium are reported with higher photosynthetic rate with lesser transpiration rate and stomatal conductance over better photosynthetic efficiency crop like maize and also this has resulted in the better withstanding ability to the water stress. Correlation analysis showed that photosynthesis and Transpiration rate are positively correlated but weak (r=0.28) and the regression equation is (Y=4.98+4.32(x)), photosynthetic rate and stomatal conductance are also positively correlated but weak (r=0.20) and the regression equation is Y= 20.36+17.04(X). Transpiration and Stomatal Conductance is positively and strongly correlated (r=0.57) and regression equation is Y=3.92+2.51(x).