Fruiting of Cotton. II. Effects of Plant Moisture Status and Active Boll Load on Boll Retention¹

Yield of cotton ( Gossypium hirsutum L .) is proportional to the number of fruits (bolls) produced, which is a function of flower production and boll retention. It bas been known for many years that a severe water deficit decreases boll retention, but tbe reports did not indicate a critical plant water status below which field‐grown plants lost bolls. Field experiments were conducted with 'DPL 70' cotton on an Avondale clay loam (a member of the fine‐loamy, mixed, hyperthermic family of Typic Torrifluvents) to a) quantify the relationship between leaf water potential (xylem pressure potential) and boll retention, and b) to assess the importance of boll load in modifying the results. Two irrigation levels were compared through the season. Boll retention was high early in the season at midday leaf water potentials from −1.4 to −1.9 MPa, but decreased when the leaf water potential decreased below about −1.9 MPa. Boll retention decreased as boll load increased. Because water deficit decreased flowering and boll retention, it limited the boll load. The feedback effect of boll load on boll retention tended to counteract the effect of water deficit on boll retention. Water deficit decreased yield, in part because of decreased flowering and in part because of decreased boll retentio