Effects of Nitrogen Fertility on Water Potential of Irrigated Cotton
Radin, J. W. | Mauney, J. R. | Kerridge, P. C.
Cotton (Gossypium hirsutum L.) grown in controlled environments responds to N deficiency with decreased hydraulic conductance and midday leaf water potential (Ψw). Experiments were initiated to determine whether N deficiency similarly affects plant water relations in the field. Cotton was grown for 4 yr with adequate N or a mild N deficiency. Nitrogen fertility had little effect on Ψw (determined with a pressure chamber) early in the season, but beginning in midseason the Ψw of N-deficient plants was 0.2 to 0.4 MPa higher than that of the fertilized plants. This difference was seen both before N had affected leaf area, and after canopy closure had occurred at both N levels. Stomatal conductances and transpiration rates of recently matured sunlit leaves (determined by steady-state porometry) remained unaffected by N. This evidence indicates that N deficiency increased plant hydraulic conductance in the field, contrary to its effect in controlled environments. However, in regressions of transpiration rate on leaf Ψw from dawn to midday, N had no consistent effects on the slopes (a putative measure of hydraulic conductance). These discrepancies have not been resolved. Nonetheless, N deficiency clearly does not decrease hydraulic conductance of cotton in the field in Arizona as it does in controlled environments.
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