Nitrogen Effects on Water Potentials of Irrigated Cotton

John W. Radin, Peter C. Kerridge, and Jack R. Mauney


In controlled environments, N deficiency is known to decrease hydraulic conductance of the cotton (Gossypium hirsutum L.) plant. Here we report N effects on plant water relations in the field in Arizona. Over four years, N deficiency consistently increased the midday water potentials (they became less negative by 0.2 to 0.4 MPa). The difference appeared beginning around day 170, or 80 days after planting. In most years, N deficiency did not limit leaf area until around day 200. Midday stomatal conductances were unaffected, as were the transpiration rates of sunlit fully-expanded leaves in the upper canopy. Although N deficiency decreased the number of bolls per plant, thereby posing the possibility that decreased reproductive growth may have somehow altered the capacity for water uptake, effects on water potential preceded effects on boll number by 30 days. Plant hydraulic conductance was estimated as the slope of the regression of single-leaf transpiration rat@ against leaf water potential as they changed during the morning. N deficiency did not alter conductance at any time during the season. These results are apparently internally inconsistent. Measurements of transpiration may be inadequate, however, because they rely upon young leaves and may not reflect water use by the entire canopy. The results are also apparently inconsistent with the model of cotton water relations developed with N-deficient plants in controlled environments. Hypotheses to reconcile these inconsistencies remain unverified.

Reprinted from 1990 Proceedings: Beltwide Cotton Production Research Conferences pg. 51
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998