Efficient Irrigation of Pima Cotton

D. W. Grimes


Newer, higher yielding upland (Gossypium hirsutum L.) and Pima (Gossypium barbadense L.) cultivars are generally shorter and earlier maturing with Pima approaching upland cultivars in these traits. With only limited information available on desired plant water relations for the currently grown `Pima S-6', a two year field study was conducted in the San Joaquin Valley (SJV), on Panoche clay loam (fine-loamy, mixed [calcareous], thermic Typic Torriorthent) of the University of California West Side Field Station in western Fresno County to evaluate contrasting water management strategies. As with upland cultivars, Pima expansive-vegetative growth was most sensitive to water stress with reduced growth observed as midday leaf water potential ( (L)) declined below -1.2 MPa. Young boll abscission was initiated at -2 MPa and reduced boll growth was observed as (L) declined below -2.3 MPa. These values are slightly lower than those generally reported for upland cultivars and appear to be associated with a higher flow resistance in Pima. Although Pima has a smaller leaf than upland cultivars that allows light penetration to greater depths in the crop canopy at a constant leaf area index, no differences were observed in crop coefficients (K(c)) between the two species. A yield-crop evapotranspiration (ET(c)) function was defined for the two year study as Y(L) (Mg ha-1) = -3.81 +3.08E-01ET(c)(1/2) -3.75E-03ET(c) (R2 = 0.93) with ET(c) in mm.

Reprinted from Proceedings of the 1994 Beltwide Cotton Conferences pp. 90 - 93
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998