Soil Water Stress and Photosynthesis in Cotton

Abstract

An experiment was conducted in SPAR systems at Florence. S.C, to obtain a data set for use in the simulation of the effect of drying soil on photosynthetic rates in cotton. The plant water status was monitored using leaf water potential and stem diameter measurements. Reductions were noted in apparent photosynthesis rales after only 5 days of soil drying, and as anticipated, there was uniform displacement of the diurnal cycle of leaf water potential, and corresponding decreases in transpiration and CO; uptake. The photosynthesis-light response curves indicated that an average twofold reduction in photosynthesis rates occurred for solar radiation greater than 250 W/nr. Stein diameter change (from a nonstress pre-sunrise value) and integrated stem stress were found to be good indicators of maximum daily plant water stress. The integrated stem stress gave a measure of the duration of the stress along with its magnitude. A simulation method for predicting leaf water potential from stem diameter measurements was used to show that the magnitude and duration of plant water stress increased uniformly during the experiment. This increase was representative of the decreased rates of photosynthesis measured. These data will be used in the simulation of cotton growth and yield.

Ethylene Inhibitors Increase Net Assimilation Rate and Cotton Boll Dry Matter Under Drought

“…Concerning to LWPpred different authors found a linear or near linear declines in cotton leaf and whole canopy photosynthesis (Pn) with LWPpred decrease (Ackerson et al, 1977;Parsons et al, 1979;Marani et al, 1985). In all cases, the decline in Pn was well established by the time LWPpred had dropped to -1.2 MPa with near 50% of Pn reductions when LWPpred reached -1.9 MPa.…”

“…The doses and entry intervals were defined based in its numbers of bolls retained in preliminary trials. After ethylene inhibitors applications, the leaf water potential at predawn (LWP pred ) (between 4:30 and 5:00 a.m.) was monitored at each two days aiming to define the key point of water status adequate to make the gas exchange analyses and sampling for photosynthetic pigments determinations (Ackerson et al, 1977;Parsons et al, 1979;Marani et al, 1985).…”

Measurement of water potential in low-level waste management. [Shallow Land Burial]

“…Generally, sensors are not interrogated more than on an hourly basis to assure that the heat pulse has completely dissipated. With appropriate calibration, these heat dissipation units have been used successfully in measuring and controlling soil matric potential under irrigated soil conditions (Phene and Beale 1976;Phene and Campbell 1975;Phene, Hoffman and Austin 1973;Parsons et al 1979). Precision of measurement in the 0 to -1 bar of matric potential range is estimated at +0.1 bar or better.…”