When modern varieties of cotton and other agronomic crops have been compared to old varieties it has been noted that photosynthetic production has been about the same. Yield improvement is partially attributable to increased harvest index of modern varieties. This has been true even though cotton has been traditionally grown in 38 to 40-inch row spacings. Wider row spacings naturally require a larger (more vegetative) plant to intercept solar radiation. With the availability of 30-inch spindle harvesters a new production system can be evaluated where smaller plant phenotypes with a higher harvest index would not be at a disadvantage.

A range of plant phenotypes were evaluated in 1982 and characterized for growth habit. More detailed evaluations for growth habit, ideal plant density, and yield potential were conducted during 1983 to 1985 at Shatter, CA. In 1985, plant phenotype by density and phenotype by nitrogen rate trials were conducted at the UC-West Side Field Station. A range in phenotypes have been evaluated in each test. The largest most vegetative plant has been Acala SJ-2. The smallest phenotype with the highest harvest index is SS2086. For simplicity only these two phenotypes will be compared in this discussion.