ticide applications needed to protect the fruit (Allen et al., 1998). Lewis (1971) further contended that cotton Cotton (Gossypium hirsutum L.) growers are faced with rising produced in an ultra-narrow row system would exhibit production costs and static or declining crop prices. One strategy with its fruiting structures at nearly identical developmental potential for reducing production costs entails growing cotton in ultranarrow rows with elevated plant populations. A 2-yr field study was stages throughout the season. This growth characteristic conducted in the Brazos Bottoms near College Station, TX to deteris in contrast to conventionally spaced cotton, which has mine the differences in vegetative growth and yield parameters of fruit at several different developmental stages at any cotton grown in ultra-narrow and conventionally spaced rows. Four particular time during the season. A more synchronized row spacings of 19, 38.1, 76.2, and 101.6 cm were planted with populafruiting pattern could possibly lead to more effective tions of 39.4 to 45.8, 18.2 to 20.7, 13.1 to 13.6, and 7.9 to 9.9 plants chemical control of insects and regulation of the plant m Ϫ2 , respectively. At crop maturity, plant height and node counts with plant growth regulators, possibly enhancing the were reduced in the cotton grown in the 19-cm row spacing. Canopy ability to increase yields. Also, producing cotton in ultraclosure occurred more rapidly in the 19-and 38.1-cm row spacings narrow rows may shift the indeterminate growth habit to than in the wider row spacings. In 1997, a relatively wet growing a more determinate one. Yield increases were obtained season, yields were not affected by the row-spacing treatments. In 1998, a dry growing season, yields in the 19-and 38.1-cm row spacings with ultra-narrow row production compared with conwere greater than those in the wider row spacings. The 19-cm row ventional row spacings in earlier studies (Briggs et al., spacing had 84.6% of the harvestable bolls at the first fruiting position 1967; Hoskinson et al., 1974). and 76.1% of the bolls on Nodes 6 through 10, both percentages being Ultra-narrow row cotton has been defined with varisignificantly greater than those observed in the wider row spacings.ous row spacings and plant populations. The row-spac-Fiber length tended to be reduced in the 19-cm row spacing relative ing constraints vary from 20.3 to 30.5 cm (Snipes, 1996) to the other row spacings. Ultra-narrow row cotton appears to be a and have also been defined as Ͻ25.4 cm . viable option for producers to attempt to reduce costs while main-

Abbreviations: Abs t , spectrophotometric absorbance at 530 nm at a specifi c water bath temperature ( t ); ETR, electron transport rate; PAR, photosynthetic active radiation; PC, principal component; REC t , relative electrical conductivity at a specifi c water bath temperature ( t ); REML, restricted maximum likelihood; T 50 , temperature (°C) at which 50% relative electrical conductivity occurred; TTC, 2,3,5-triphenyltetrazolium chloride.

Ultra‐narrow row cotton (Gossypium hirsutum L.) production is considered a potential strategy for reducing production costs by shortening the growing season. A 2‐yr field study was conducted near College Station, TX, on varying soil types to document phenotypic alterations and crop maturity differences for cotton grown in 19‐, 38‐, 76‐, and 101‐cm row spacings. In the 19‐cm rows, the plant densities were 12.2, 18.8, and 40.5 plants m−2 Densities of 11.3 and 19.5 plants m−2 were established in the 38‐cm rows. In the 76‐ and 101‐cm rows, plant densities of 11.7 and 7.4 plants m−2, respectively, were evaluated. Plant height and node counts were reduced in the narrow (19 and 38 cm) row spacings in only 1 yr. The narrow row spacings at the higher plant densities consistently accumulated leaf area index more rapidly than the conventional (76 and 101 cm) row spacings. In 1998, when the study was conducted on a heavy clay soil, the higher plant densities in the 19‐ and 38‐cm row spacings tended to partition more biomass to reproductive structures and yielded more than the conventional row spacings. In 1999, the test was conducted on a lighter silty clay loam soil and yields were unaffected by the row‐spacing treatments. In 1998, the higher plant densities in the 19‐ and 38‐cm row spacings had a greater percentage of harvestable bolls at the first fruiting positions on lower nodes, a boll distribution pattern that contributed to earlier crop maturity. Narrow row spacings and high plant densities did not consistently alter fiber quality. No conclusive differences for crop growth and development could be ascertained between the medium and high plant densities in the 19‐ and 38‐cm row spacings. However, ultra‐narrow row cotton may be more advantageous to producers when grown on heavier soils that typically do not promote excessive vegetative growth.

et al. (1984) found that although MC-treated plants had as much as 33% less leaf area as untreated plants, no Few studies have documented the effects of mepiquat chloride differences in seasonal water use were detected between (MC) (1,1-dimethyl piperidinium chloride) and PGR-IV [0.001% (w/v) indolebutyric acid (IBA), 0.001% gibberellic acid (GA)] on untreated plants and plants treated with MC. flowering. This study was conducted in an effort to better understand Other effects of MC treatment include increased fruit the effects of these two plant growth regulators (PGRs) on cotton retention, earliness, and yield enhancement. Jung et al. (Gossypium hirsutum L.) flowering when applied alone or used in (1975) found that MC treatment offset conditions leadsequential applications. Field experiments conducted in 1996 and 1997 ing to square abortion; while Cathey et al. (1988) found at the Texas A&M University Agricultural Experiment Station near MC increased flower production in late-planted cotton. College Station, TX, contained the following treatments: an untreated Earlier maturity is frequently a response to MC treatcontrol, MC, PGR-IV, and a combination of both MC and PGR-IV ment (York, 1983a; Kerby, 1985). MC increases earlyapplied sequentially (PGR-IV ϩ MC). The MC and PGR-IV ϩ MC season fruiting and decreases the number of late-season treatments caused plants to have a season-long average of 0.55 and bolls (Kerby et al., 1986). Although yield increases have 0.48 more flowers m Ϫ1 of row d Ϫ1 , respectively, than the untreated plants. All PGR treatments resulted in a higher rate of flowering than been reported as a result of MC applications (Willard et untreated plants between the 16th and 20th d of flowering. The MC al. Kerby, 1985), other research has found erratic treated plants also had 19.1 more total flowers per meter than PGRyield responses (Stuart et al., 1984;Cathey et al., 1988; IV treated plants by the 40th d of flowering. Treatment effect onYork, 1993a,b). Zhao (1993a, 1994a,b) reported inthe 36th and 40th d of flowering. At this time, the PGR-IV ϩ MC creased rooting in response to PGR-IV applications, a treated plants had a greater flower survival than plants treated with result that may have been caused by the IBA in the only PGR-IV. All PGR treatments resulted in increased yields and product. By increasing the root mass with IBA and boll numbers. These studies indicate that the application of MC and promoting plant growth with GA, PGR-IV may enhance PGR-IV, either in sequential applications or alone, increases both the plant's ability to tolerate drought and other environthe rate of flowering and the number of flowers per meter of row, but does not impact the ability of flowers to survive to maturity. St. Suite 305, Sweetwater, TX 79556; J.T. Cothren, Texas A&M University, Soil and Crop Sciences Department, College Station, TX 77843-2474. flower survival was different only for flowers that bloomed between

High night temperature (HNT) is among the important abiotic stresses limiting rice production. The impacts of abscisic acid (ABA) on higher plants have been the subject of many studies. However, little or no work has been performed on rice responses to ABA under HNT‐stress conditions. This study determined the effects of ABA on rice leaf photosynthetic rate (PN), photochemistry, respiration, and physiology under HNT. Plants were grown under ambient night temperature (ANT; 25°C) or HNT (30°C) with or without ABA (100 ppm) application from the boot stage of rice plants until harvest. The HNT decreased rice yield (11%), which was associated with decreasing PN (5%), pollen viability (11%), and spikelet fertility (5%) and increasing respiration rate (44%). In addition, HNT decreased grain width (4%) and increased grain chalkiness (65%), thereby decreasing grain quality. The ABA‐treated plants showed increased yield (15%) as a result of increased PN (6%) and spikelet fertility (6%) and decreased respiration (33%), under HNT. The increased PN under HNT as a result of ABA application is associated with increased stomatal conductance (22%) and decreased nonphotochemical quenching (NPQ; 29%). In addition, ABA‐treated plants grown under ANT also showed increased yield (9%) as a result of increased PN (7%) and spikelet fertility (7%) and decreased respiration (16%). The increased PN under ANT as a result of ABA application was due to increased quantum yield (8%) and electron transport rate (8%). This study shows that exogenous application of ABA has the potential to increase rice yields under HNT.

In a 2-yr field study conducted on a Weswood silt loam soil (Fluventic Ustochrepts), interspecific competition between soybeans [Glycine max(L.) Merr. ‘Hutton′] and velvetleaf (Abutilon theophrastiMedik. # ABUTH) resulted in greater than 40 and 50% reductions in soybean and velvetleaf seed yield, respectively. Leaf area index, number of mainstem nodes, total number of leaves, and plant dry weight of monocultured and intercropped velvetleaf differed significantly as early as 4 weeks after emergence. Interspecific competition had litttle or no effect on soybean morphology before 8 weeks after emergence. Soil water extraction occurred to 1-m depths in a monoculture of velvetleaf (five plants/m2) in 1984 and 1985. Monocultured soybeans (32.5 plants/m2) extracted water from a 1.5-m or greater depth of the soil profile during the same years. Soil water extraction in the intercropped plots resembled that of the monocultured velvetleaf treatment until soybeans attained R6, when soil water was extracted to a 1.5-m depth. The potential for interspecific competition for water existed early in the season before late-season soybean root development. Relative water content and leaf water potential (Ψw1) did not differ (0.05) between monocultured and intercropped soybeans in 1984 or 1985. In 1985, Ψw1differed between monocultured and intercropped velvetleaf during anthesis. Leaf water potential values in the youngest, fully expanded leaves were approximately 0.3 and 0.4 MPa lower during midmorning and midday hours, respectively, in intercropped and monocultured velvetleaf. Transpiration and stomatal conductance did not differ between monocultured and intercropped soybeans or velvetleaf at any time during 1984. Photosynthetic and transpiration rates, stomatal conductance, and Ψw1were lower in intercropped than in monocultured velvetleaf during anthesis in 1985, suggesting interspecific competition for soil water. Soybean water relations were not affected in either year. The data suggest that soybean yield reductions in soybean-velvetleaf interspecific competition are attributable to resource limitations other than water in south-central Texas.

Nitrogen fertilizer requirements of ultra‐narrow row (UNR) cotton (Gossypium hirsutum L.) are not well established, and lint yield of UNR relative to conventional‐row (CR) cotton has been variable. Objectives of this study were to compare UNR and CR N requirements based on lint yield, fiber quality, and plant architecture, and to compare the yield potential of UNR and CR cotton. The location was the Texas Agricultural Experiment Station Farm, Burleson County, TX. Treatments were N fertilizer rates of 0, 50, 101, and 151 kg ha−1 and row spacings of 19, 38 (both UNR), and 76 cm (CR). By design, per‐hectare plant populations were greatest in 19‐ and least in 76‐cm row spacings. Plots were hand harvested. Reductions in row spacing decreased plant height, main stem nodes plant−1, and subset (first position bolls at nodes 6–10) individual boll weight. Greater N increased plant height, main stem nodes plant−1, and both whole‐plant and subset individual boll weight. Lint percentage was increased by reduction in row spacing and not affected by N. Treatment effects on fiber quality were limited. Lint yield did not differ among row spacings. Significant increases in lint yield occurred with each increase in N, suggesting that the optimal N rate was not surpassed. Nitrogen by row spacing interaction on lint yield was not significant, implying a similar response of each row spacing to N over the fertilizer rates tested. The N fertilizer requirements of UNR do not appear to be lower than those of CR cotton.

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