EXP-SlO89 is an experimental plant growth regulator of natural origin. The major ingredients are carboxylic acids. Field and controlled environment studies were conducted to investigate its effects on nutrient uptake, photosynthesis and levels of different sugar components of Cotton (Gossypium hirsutum L.) plants, using the cotton cultivar Deltapine 51. In the controlled environment study at the Altheimer Laboratory, Fayetteville, Arkansas, the growth chamber was programmed for a 12-h photoperiod with a day/night temperature of 25/20 C. Lighting was provided by overhead fluorescent and incandescent bulbs. Cotton seeds were germinated in vermiculite and plants were transferred to 4-L jars containing full strength modified Hoaglands nutrient solution. At 4-leaf stage, EXP-SlO89 was foliarly applied at 0, 1, 2 and 4 pt./acre equivalent. The experimental design was a randomized complete block with 4 replications. Nutrient solution in which plant roots were growing was sampled at time intervals after bringing the solution to the original level with deionized water. K, Ca, Mg and P in the nutrient solution sample was determined using a Plasma 300 ion analysis unit, and the amount of nutrient taken up by the plant was calculated. About 20 days after the treatment, plants were harvested, and the carbohydrate levels in plant dry matter were determined on high performance liquid chromatography.

The field experiment was conducted on a Loring-Calloway silt loam at the University of Arkansas Cotton Branch station, Marianna, Arkansas. Cotton was planted on May 9, 1992, in 4-row plots 10 m long. The row spacing was 90 cm with plants 12.5 cm apart. Treatments consisted of a control with no EXP-SlOB9 added and a foliar treatment with EXP-SlO89 at 2 pt./acre applied at first flower and two weeks later. The experimental design was a randomized complete block with 5 replications. At peak flowering, 50 white flowers at the first fruiting position of sympodial branches were tagged on the same day in the middle two rows of each plot. Photosynthetic rate of 3 tagged sympodial leaves in each plot was measured about every two weeks using a LI-6200 portable photosynthesis system.

In the growth chamber, foliar application of EXP-SlO89 at 2 pt./acre, or higher, greatly increased the uptake of all the four elements investigated. Compared with the control, plants treated at 2 pt./acre had more sucrose in the stem, and less in the leaves and roots; while glucose and fructose were generally opposite. In the field, EXP-SlO89 increased the photosynthetic rate of cotton leaves on all the measuring dates. The most significant increase was found two weeks after flowering, when a 61.6% increase was detected. This, along with the increased nutrient uptake, might be responsible for the increase in boll setting, boll size, and yield.