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COTTON

Influence of Ultranarrow Row and Conventional Row Cotton on the Last Effective Boll Population

^a USDA-ARS-SRRC, Sugarcane Res. Lab., Houma, LA 70360
^b Dep. of Plant Sci., Univ. of Tennessee, Jackson, TN 38305
^c Dep. of Soil and Crop Sci., Texas A&M Univ., College Station, TX 77843
^d Dep. of Entomology and Plant Pathology, Mississippi State Univ., Mississippi State, MS 39762
^e USDA-ARS, Cropping Systems and Water Quality Res. Unit, Portageville, MO 63873
^f USDA-ARS, National Peanut Res. Lab., Dawson, GA 39842-0509
^g Dep. of Crop Sci., North Carolina State Univ., Raleigh, NC 27695-7620. Funded by Cotton Incorporated

^* Corresponding author (ryan.viator{at}ars.usda.gov).

The last effective boll population (LEBP) is the basis for many cotton (Gossypium hirsutum L.) management decisions such as defoliation timing. The objective of this research was to determine the last effective boll population based on first position bolls for both ultranarrow row cotton (UNRC), grown in rows spaced 25 cm or less, and conventional cotton (CONC) grown in rows spaced 96 to 102 cm. Experimental sites included locations in North Carolina, Tennessee, Mississippi, Arkansas, and Texas. At each site, UNRC and CONC plots were planted in a RCB design. At first flower, 15 plants per plot were flagged for subsequent flower tagging. On each flagged plant, all first position flowers were tagged every 2 d throughout the reproductive stage with date and nodes above white flower (NAWF) data for each plant. Tagged bolls were handpicked, sorted, counted, and seedcotton was weighed and recorded by NAWF for each plot. The last effective boll population was considered that NAWF position where cotton could be economically produced. Cotton could be produced economically at NAWF 2 and 3 for UNRC and CONC, respectively. Lint yield did not differ significantly between UNRC and CONC across site-years. The UNRC produced the majority of seedcotton on NAWF 3 to 5, while CONC produced the most seedcotton at NAWF 4 to 6. Boll numbers showed a similar pattern. These data demonstrate that physiological cutout occurred at NAWF <5 in both UNRC and CONC.

Abbreviations: CONC, conventional cotton • LEBP, last effective boll population • NAWF, nodes above white flower • UNRC, ultranarrow row cotton

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Received for publication August 27, 2007.