Cotton (Gossypium hirsutum L.) plants with okra or superokra leaves have several agronomic characteristics which could make them better adapted to narrow‐row culture than plants with normal leaves. This study was conducted to investigate the effect of these leaf types on canopy photosynthesis and transpiration of narrow‐row cotton. A portable, open‐chamber system was used in plant communities grown at high and low densities. In 1973 the three leaf types (normal, okra, and superokra) had dissimilar genetic background with the okra and superokra leaf lines being similar in appearance and leaf area. Maximum leaf area index (LAI) these canopies was approximately 2.8 compared to 4.6 for normal leaf plants. Near‐isogenic lines were used in 1974. Although morphologically distinctive, the okra and normal isolines had maximum LAIs of approximately 5.2, compared with 3.5 for the superokra leaf isoline. Apparent photosynthesis was positively associated with LAI, although correlation coefficients were low (0.23 to 0.54). Plant population had little effect on canopy photosynthesis. When data were averaged across populations, normal leaf plants had CO2 exchange rates 20 and 29% higher than superokra leaf plants in 1973 and 1974, respectively. Okra leaf plants were intermediate. Leaf type effects on transpiration were small and inconsistent during the 2 years. Although differences in photosynthesis to transpiration ratios statistically nonsignificant, the trend was normal>okra> superokra. Thus, the okra leaf types do not appear to be associated with improved efficiency of water use.

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A two year field study (1996/97 and 1997/98 growing seasons) was carried out at the Maricopa Agricultural Center (33º04'07" N; 111º57'18" W) of the University of Arizona, USA, to investigate the water use and to derive Kc's for subsurface drip-irrigated head lettuce grown in small weighable lysimeters. Measurement periods ranged from 480 to 1100 ºC-day (96/97) and from 439 to 1098 ºC-day (97/98). These intervals corresponded essentially to the second half of the crop cycle which amounted to a 1100 ºC-day, on average. The lysimeters were weighed periodically and the computation of the water balance revealed an average water use of 117 mm. Basal crop Kc was expressed as a function of cumulative growing degree days following a multiple linear regression procedure in which the data were fitted with a Fourier sine series model with up to six coefficients. Two-year Kc curves were obtained based on the Hargreaves, FAO Penman and FAO Penman-Monteith equations and compared to the AZSCHED (AriZona SCHEDuling) irrigation package. Predicted Kc peaked 0.88, 0.80 and 0.81 with the Hargreaves, FAO Penman, FAO Penman-Monteith equations, respectively, in the range of 1000 to 1050 ºC-day, in contrast to AZSCHED which predicted the peak Kc to be 1.01 at 1150 ºC-day.

Successful modeling of cotton (Gossypium hirsutum L.) seedling emergence requires a model capable of simulating hypocotyl growth under a wide range of soil environments. A previous model used an autocatalytic growth equation which was satisfactory for relatively favorable soil environments. We report here the use of the Gompertz equation as a hypocotyl elongation model which should have adaptability to greater environmental extremes than the autocatalytic model. A three parameter form of the Gompertz equation was applied to a comprehensive set of cotton hypocotyl elongation data, obtained over a range of steady‐state soil environments. The form used was y = A exp {—exp [b(c—t]} where y is hypocotyl length at time t, A is maximum (potential) hypocotyl length under prevailing soil conditions, b is the weighted mean relative growth rate, and c is the time at which maximum growth rate is attained. This function describes an asymmetrical sigmoid curve in which all parameters can be assigned physiological meaning. Best‐fit estimates of the Gompertz parameters were derived for hypocotyl elongation in each environment by a non‐linear least squares program. Multiple linear regression analyses of the estimated Gompertz parameters (in normalA∘, normalb∘, and normalc∘) with soil temperature, physical impedance, and moisture were used to examine the influence of soil environment on the parameters. Each of the three Gompertz parameters were adequately described by a cubic regression model involving these soil factors. The regression models were used to develop a Gompertz model in which each parameter was responsive to fluctuating changes in soil environment. The model should be adaptable to simulating cotton hypocotyl elongation under a wide range of soil conditions, including those resulting in seedling stress.

Seed germination and seedling development are adversely affected in many crops by less than lethal chilling temperatures. Periods of chilling sensitivity have been identified in Upland cotton (Gossypium hirsutum L.) but little work has been reported in Pima cotton (G. barbadense L.). This study was conducted to evaluate the influence of temperature on the degree and timing of chilling susceptibility in germinating Pima cotton and to determine if genetic variability exists. Seed were germinated at 25 or 35 C for 72 hours with one additional 24‐hour chilling exposure of 5, 7, or 10 C at various times during germination. Two periods of chilling sensitivity were noted. The first occurred at the beginning of germination. The second period showed maximum sensitivity between 28 and 32 hours when seed were germinated at 35 C and between 40 and 56 hours when seed were germinated at 25 C. Chilling at 7 C during both sensitive periods delayed emergence from a soil mix. In addition, final emergence was reduced by 26% when seed were chilled at the beginning of germination. Chilling at 5 C caused much more severe damage than chilling at 7 or 10 C. Some experimental lines showed greater resistance to chilling than the commercial cultivar, ‘Pima S‐4.’ Two genetic lines that responded similarly when chilled at 5 C differed significantly when chilled at 7 and 10 C. This suggests that these higher temperatures may be best for evaluating genetic variation and seed treatments to impact chilling resistance.