Diurnal patterns of photosynthesis, evapotranspiration and water use efficiency in barley under field conditions

On clear days, PN increased from initial vegetative phase through anthesis and declined thereafter till maturity. Diurnally PN followed the course of photo-synthetically active radiation (PAR: 400–700 nm) from tillering to anthesis, but declined at high PAR intensity during grain filling stag of crop development. There was a lag of about 2 h. between PNmax and ETmax. Water use efficiency increased from vegetative stage to flowering and decreased thereafter till maturity. Diurnally WUE was markedly low at higher PAR density during raid-day hours, but showed a slight recovery in the late afternoon. The WUEmax was recorded between 8–10 h. around 300 μE m⁻² S^-1 PAR intensity. This study suggested that high temerature during grain development could be limiting factors for attaining high PN rates and grata yield in late sown barley under North Indian conditions.