Environmental stress and boll load have both been suggested as responsible for the fruiting cessation (cut out) that occurs in cotton (Gossypium hirsutum L.) in mid‐summer in the hot, desert southwestern USA. This study was conducted to examine the influence of boll load on the flowering hiatus. Two cultivars differing in growth habit were planted in the field on an Avondale clay loam soil, a member of the fine, loamy, mixed Hyperthermic Torrifluventic Haplustolls. ‘Deltapine Smooth Leaf’ (DpSL) has a more determinate growth habit than ‘Acala 44–10’ (A‐44). Fruiting was limited during a 90‐day period within each year. Flowers in excess of one flower per plant per time interval, ranging from 2 to 5 days, were removed. Flowers left on plants were tagged and used to calculate boll retention curves. Limiting the number of flowers retained increased total flower production with DpSL more responsive than A‐44. Defloration resulted in cycling of the flower production curve which appeared to be related to relief of moisture stress either from irrigation or rain. Defloration increased both total and percent boll retention during the normal period of cessation of new vegetative and flowering growth with DpSL being more responsive than A‐44. We conclude that boll load exerts a large influence on fruiting behavior of cotton and is the major controlling factor of the cut out period in the cultivars tested.

The optimum plant density for narrow‐row cotton (Gossypium hirsutum L.) is influenced by the lint yield response to plant density as well as other crop characteristics affecting crop management. This study was conducted to quantify the effect of population density on many of these characteristics. Three experiments were conducted with narrow‐row cotton in population densities ranging from 7.1 to 22.9 plants/m2. In August plants were harvested at ground level and morphological measurements were made. At the end of the growing season lint yield was determined. There were no statistical effects of plant density on lint yield or boll and fiber properties. Population pressure increased plant height when plants were young, while the effect on older plants was inconsistent. The morphological measurements showed (a) each five plants/m2 increase in, plant population decreased the number of mainstem nodes by one, (b) each eight plants/m2 increase in population decreased the number of monopodial branches per plant by one, (c) each 11 plants/m2 increase in population density raised the lowest sympodial branch with a boll by one node. In addition increasing density from about seven to 30 plants/m2 reduced the percentage of bolls supported by monopodial branches in a curvilinear manner from 25 to 0. Increasing plant density, also increased leaf area density, especially in the central portion of the plant canopy. Considered with their probable influence on harvesting efficiency, incidence of diseases and insects, and chemical defoliation, these data should help in predicting the optimum population for narrow‐row cotton. For these studies the optimum appears to be between 10 and 15 plants/m2.

Previous research with narrow‐row cotton (Gossypium hirsutum L.) has concentrated on end‐of‐season effects on yield and fiber characteristics with little attention given to seasonal fruiting patterns. Our objective was to monitor the seasonal fruiting pattern of cotton planted at various combinations of row spacings and plant densities. ‘Deltapine 16’ was grown 3 years on one or two rows per beds that were either 76 or 102 cm from center to center with densities of 7.4, 14.8, and 22.2 plants/m2. The plots were divided into flower tagged (tagged plots) and yield portions (yield plots). In the tagged plots, flowers were tagged daily with the date of anthesis. Open bolls were harvested weekly and assigned to weekly flowering intervals before being analyzed for boll and fiber properties. Before harvesting the yield plots, we also took open boll samples to be analyzed for boll and fiber properties. At equivalent plant densities in the yield plots, two rows per bed resulted in up to 11% more seedcotton than one row per bed. Plant density had no significant effect on yield. In the tagged plots, seasonal flower and boll production was higher from two rows per bed than one row per bed with differences ranging from 8 to 22% more flowers and 2 to 12% more bolls, depending upon bed size and plant density. The seedcotton yield advantage of two rows per bed was near maximal from bolls that were set (flowered) by late July; thereafter the production rate on one and two rows per bed was similar. Boll period (time from flowering to open boll) was increased slightly by high plant density. Boll size, lint index, seed index, fiber strength, and fiber fineness from the yield plots were all significantly reduced by increases in plant density, although the average effects were less than 5%. While fruiting pattern and yield were primarily influenced by row spacing, plant density had the greatest influence on boll and fiber properties.

Previous research has shown that germination of cottonseed (Gossypium spp.) can be improved during low temperature by treating seed with gibberellic acid (GA3), kinetin, or by elevating the seed moisture level. The work reported here was conducted to evaluate these seed treatments as aids to improving seed germination of G. barbadense L. (‘Pima S‐4’) and to determine if they enhance seedling emergence in fields with low soil temperatures. Soaking seed in water for 6 hours before chilling at 5 C significantly reduced visual chilling injury. Both kinetin and GA had little effect on % germination, but vigor of germinating seed was increased in the laboratory when seed were soaked for 3 hours in 0.1 or 1.0 mg/liter kinetin, or 100 or 500 mg/liter GA. When similar seed treatments were evaluated in several field plantings with low soil temperatures, neither chemical improved the number of seedlings emerged or the time required for emergence. GA at the level that promoted seed vigor in the laboratory resulted in greatly reduced emergence because of spindly growth. Soaking seed in water before planting generally reduced emergence with the degee of reduction directly related to length of soaking. Seed that were soaked for 3 hours showed abnormal development of cotyledons and reduced dry wt. compared to nonsoaked seed. Thus these seed treatments cannot be recommended as aids to enhance Pima cotton seedlings emergence.

Better predictive methods of field emergence of cotton (Gossypium spp.) seedlings are needed than are presently available. In this paper we report on two types of relationships for predicting seedling emergence. The first is the association between field emergence and a vigor term of germinating seedlings called % transfer (ratio of plant axis weight to total weight of seedlings). The second is the relationship between time to 50% total emergence (ET50) and total emergence. Seed of diverse origin were germinated in the laboratory at 15 C for 8 days or at 25 C for 4 days and % germination, and % transfer were determined. Several field plantings were made, and periodic counts were made as seedlings emerged. The time course of germination of two lines that responded differentially in germination and field studies was examined by taking weights and seedling axis lengths repeatedly for 4 days at 25 C and 14 days at 15 C. Germination at 15 C for 8 days did not consistently predict field emergence better than germination at 25 C for 4 days. Some improvement occurred when germination parameters were averaged for the two temperatures. Combining % transfer with % germination into a term called “germination index” did not consistently aid in predicting field emergence over use of % germination alone, apparently because seed with high viability generally produced vigorously germinating seedlings. Percent transfer was negatively correlated with ET30. Predictability of the germination parameters was improved by extending the length of the germination period. Total emergence decreased linearly with increase in ET50. The average decrease ranged from just under 2% per day of ET50 to over 4% when the test involved a salt‐affected soil. We conclude that incorporation of these seed vigor terms into seed testing will not aid in predicting potential for cottonseed emergence. The relationship between emergence and ET50 should serve as an aid in making early decisions about replanting, although the nature of the relationship will probably depend upon local soil conditions.

We previously reported large variation in field emergence of commercially processed cottonseed (Gossypium barbadense L.) produced within a small geographical area of Arizona. The current investigation was conducted to determine if there were important management practices associated with the variation in seed vigor. An examination of the seed in question showed that much of the variation was associated with date of ginning and harvesting. Seed ginned after November were generally of low quality for planting purposes. To determine if low quality of late‐ginned seed cotton was associated with field weathering and/or the contribution of low quality seed in late matured bolls, open bolls of ‘Pima S‐5’ (G. barbadense) and ‘Deltapine 61’ (G. hirsutum L.) were harvested periodically during two autumns. The bolls were either exposed to various lengths of field weathering or had matured at different times during the harvest period. The seed was evaluated the following spring for germination, field emergence, and plant growth. Date of maturity had a greater effect on seed vigor than field weathering although both generally caused significant effects. Seed germination and emergence were influenced to a greater extent than plant height taken in the early summer or the date of initial flowering. Although the effect of date of maturity was greater than that of field weathering, the latter would be expected to affect a greater quantity of seed. This study stresses the importance of timely harvesting in order to obtain high quality planting seed.