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The effect of plant and leaf age on CO2-exchange rates (CER) and transpiration rates in 15 genotypes of cassava (Manihot esculenta Crantz) was measured in situ by infrared gas analysis. The plants were grown in a controlled-environment room with a 14-h photoperiod, day–night temperatures of 29–24 °C, and 60–70% relative humidity.Plant age had no effect on leaf CER, whereas transpiration rates in 14-week-old plants were significantly greater than those in 7-week-old plants. Both CER and transpiration rates decreased with leaf age. The decline was negligible when measured at low photosynthetic photon flux density. At saturating light, however, both CER and transpiration rates decreased significantly in most of the genotypes. Significant genotypic differences were observed in the pattern of decline. Both stomatal (rs) and residual (rr) resistances to the diffusion of CO2 increased with leafage in all the genotypes. The relative increase in rr was much greater than the increase in rs. In all the genotypes the ratio rr:rs was greater than unity, suggesting that rr is the major component of the total resistance to photosynthesis. Chlorophyll content and specific leaf weight also varied significantly among the genotypes. However, chlorophyll content decreased and specific leaf weight increased with leaf age.

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Water scarcity constrains global cotton production. However, partial root-zone drying (PRD) and mulching can be used as good techniques to save water and enhance crop production, especially in arid regions. This study aimed to evaluate the effects of mulching for water conservation in an arid environment under PRD and to further assess the osmotic adjustment and enzymatic activities for sustainable cotton production. The study was carried out for 2 years in field conditions using mulches (NM = no mulch, BPM = black plastic mulch at 32 kg ha-1, WSM = wheat straw mulch at 3 tons ha-1, CSM = cotton sticks mulch at 10 tons ha-1) and two irrigation levels (FI = full irrigation and PRD (50% less water than FI). High seed cotton yield (SCY) achieved in FI+WSM (4457 and 4248 kg ha-1 in 2017 and 2018, respectively) and even in PRD+WSM followed by BPM>CSM>NM under FI and PRD for both years. The higher SCY and traits observed in FI+WSM and PRD+WSM compared with the others were attributed to the improved water use efficiency and gaseous exchange traits, increased hormone production (ABA), osmolyte accumulation, and enhanced antioxidants to scavenge the excess reactive oxygen. Furthermore, better cotton quality traits were also observed under WSM either with FI or PRD irrigation regimes. Mulches applications found effective to control the weeds in the order as BPM>WSM>CSM. In general, PRD can be used as an effective stratagem to save moisture along with WSM, which ultimately can improve cotton yield in the water-scarce regions under arid climatic regions. It may prove as a good adaptation strategy under current and future water shortage scenarios of climate change.

Rice is an important crop and the food security of the world is strongly associated with it as it is the staple food of half of the world's population. Among various agro-management practices seedling age and nitrogen rates significantly affected its growth, development and yield components. Rice cultivars performed differently when transplanted in field at varying seedling ages depending upon their genetic makeup and adoptability to certain environmental conditions. Seedling age plays an important role in yield contributing parameters like number of productive tillers, panicle length, filled grains panicle −1 and 1000-kernel weight leading to higher paddy yield in different rice cultivars and hybrids. Nitrogen is required in huge quantity in rice production as it is an important constituent of plant parts and processes. Paddy yield increases significantly with the increase in nitrogen rate but after a certain limit yield starts decreasing. Keeping in view the significance of seedling age and nitrogen rates in different rice cultivars and hybrids, an effort has been made to review some research work already conducted and will be helpful to the researchers and scientists to plan future strategies.