ABSTRACT

Boll development of late planted cotton (Gossypium hirsutum L.) in the Southeast USA often occurs when temperatures are below optimal for cotton. Since some of the physiological functions of K in plants are also regulated by temperature, late planted cotton may respond differently to K fertilization than cotton seeded at normal planting dates. We conducted this research to determine the impact of K fertilization, planting date, and genotype on cotton yield and earliness.

A field experiment was conducted at Clemson University's Pee Dee Research and Education Center in Florence, SC in 1991 and 1992 on a sandy loam soil. Treatments in the experiment were K levels of 0 or 100 lbs/acre, planting dates of early May and late May, and five PO germplasm lines. The genotypes evaluated were PD 5246, PD 5286, PD 5358, PD 5472, and PD 5582. Experimental design was randomized complete block in split-plot arrangement. Main plots were the planting date by K level combinations and subplots were genotypes. There were three replicates each year.

Earliness was determined by measuring the number of days needed for flowers to develop into harvestable bolls. Dated tags were placed on white flowers in one (1992) or two (1991) m of row each week (Monday through Friday) from July through August each year. Tags were collected daily from September through October when bolls were considered open enough to be harvested by a spindle picker. When all tagged bolls were open in a planting date, plots were harvested with a spindle picker and yield was determined.

Neither potassium level nor planting date affected lint yield either year. At the beginning of the experiment, soil test levels in the top eight inches of the soil profile were 95 lbs of available K per acre. Apparently, this amount of K (plus subsoil K) was adequate for cotton as mean lint yield was over 1000 lbs per acre in 1991. In 1992, lack of heat units through the season and a lack of precipitation during June and July caused low lint yield (the experiment averaged less than 500 lbs per acre).

In general, added K delayed boll opening by a few days in the early planting date both years. In the late planting date, the earliness of PD 5286 and PD 5472 were not influenced by K fertilization either year. Average time from white flower to open boll in the late planting date for PD 5358, however; was about 6 days longer in 1991 and 3 days longer in 1992 with added K. Although additional research is needed, these data suggest that soil K fertility status may be an important factor for breeding programs that are developing genotypes for shortseason production systems.