Charles Baldy

Sorghum yield, water use and canopy temperatures under different levels of irrigation

Abstract This research was initiated to examine water use of differentially irrigated sorghum (Sorghum bicolor (L.) Moench) and to evaluate the plant water stress using canopy temperature measurements. Field experiments were conducted for 3 years characterised by different weather conditions at Montpellier, France. The crop was subjected to 14 differentially irrigated treatments which included, each year, a full irrigated and a dry treatment. Plant and soil measurements monitored during the crop cycle included soil water content, leaf water potential, and canopy temperature. Mid-day measurement of crop canopy temperature (Tc) /air temperature (Ta) difference reached a maximum of 7°C in the dry treatment and was maintained close to 0°C in full irrigated treatment. The relationships between (Tc-Ta) and vapour pressure deficit (VPD) commonly referred to as ‘baseline’ in the determination of crop water stress indicator (CWSI) were examined on function of wind speed and global solar radiation. Three approaches of estimating CWSI were compared. Summations of stress-degree-day (SDD) and temperature-stress-day (TSD) were well related to both relative evapotranspiration and yield (r2 > 0.70).

Diurnal course of canopy temperature and leaf water potential of sorghum (Sorghum bicolor L. Moench) under a Mediterranean climate

Abstract This paper reports the diurnal behaviour of canopy temperature and leaf water potential of Sorghum bicolor L. Moench in a field experiment conducted in 1990 and 1991 on a deep soil at Montpellier (France). The crop exhibits the typical diurnal trends in its leaf water potential and canopy temperature. The predawn values of leaf water potential were high in both well watered and stressed treatments (−0.2 to −0.5 MPa) and the difference in values between the two treatments were very small. However, minimum values were observed at solar noon and the differences in values observed at this time between the two treatments were as high as 1 MPa. Canopy temperature as well as canopy-air temperature difference were considerably higher in stressed treatment than in well watered treatment during the daytime. High correlation in the linear relationship between canopy-air temperature difference (Tc - Ta) and the air saturation vapor deficit for the well watered plot was observed.

Biomass of grain sorghum (Sorghum bicolor L. Moench) under variable water regime

Abstract Field experiments were carried out for three years at Montpellier, France in a deep collovial alluvial soil during summer to study biomass production of grain sorghum ( Sorghum bicolor (L.) Moench) under water stress. All treatments were well watered at sowing to ensure good crop emergence. Grain sorghum biomass showed substantial variation between treatments. Grain yields varied from 3.8 tha −1 in highly stressed treatment to 10.7 tha −1 in well watered treatment. The number of panicles per unit area was greatly influenced by the level of water regime at booting stage. Water deficit at maturity affects seed weight. However, a compensatory effect was observed on the yield components of sorghum under the different treatments owing to differences in plant population.

Contribution a l'etude de la repartition du rayonnement d'origine solaire dans des couverts de pins

Abstract Two series of measurements of solar radiation were made under pine trees using original linear pyranometers (Fig. 1). Under a canopy , the local intensity of radiation is modified by the density of the trees (Fig. 4) and the situation of the meter in the tree modifies the incoming energy more than the height of measurement over the soil level (Fig.6). The energy incoming to the soil depends on the apparent height of the sun. The percentage of incoming energy under a canopy is greater on a cloudy day than by clear weather, but the absolute energy level is lower (Fig.5). Shadow reduces usable energy at soil level under an isolated pine, but the ratio visible/infrared is only slightly modified (Fig.7). Possible developments of this technique are studied, and the small number of studies on this subject is emphasized.