Widespread potassium (K) deficiency has occurred across the Cotton Belt, supposedly due to the use of higher-yielding, faster-fruiting cotton cultivars. Preliminary research has shown that these deficiencies can be corrected by foliar fertilization with KNO₃. Foliar application of K may offer the opportunity of correcting these deficiencies quickly and efficiently, especially late int he season when soil application of K may not be effective. While there are many reports on research involving soil applied K. much less in known about the usefulness of foliar applied KNO₃, compared to soiled-applied KCl, for alleviating K-deficiency and improving (Gossypium hirsutum L.) yield and fiber quality.

The trial was planted at twelve sites, including Marianna, Arkansas; Belle Mina, Alabama; Tuscon, Arizon; Hanford, California; Merced, California; Stoneville, Mississippi; Portageville, Missouri; Laure Hill, North Carolina; Tifton, Georgia, Jackson, Tennessee; College Station, Texas; and Lubbock, Texas. At all sites the recommendations from preplant soil tests, (3) high-soil-K preplant (double the recommended level in treatment 2), (4) low-soil-K-plus foliar-K, and (5) high-soil-K-plus-foliar-K. The foliar rate was 1- lb KNO3/acre at 2,4,6, and 8 weeks after first flower. Whenever KNO₃ was added to the two foliar treatments as foliar urea to negate the possible effect of the added nitrogen in the foliar KNO₃ treatments.

The preplant soil test potassium levels varied widely, from a low of 139 lb K/acre (North Carolina) to a high of 800 lb K/acre (Lubbock, Texas); the average for the potassium treatment on seedcotton yield was very variable, with significant differences in only three of the twelve locations ( Alabama, California, and North Carolina). However, in view of the current interest in foliar fertilization with potassium, the overall trends in this preliminary data may by of some interest. The soil-added-K treatments tended to increase yield (by an average of 150 lb/acre) compared to the untreated control at all except three locations: Georgia, Mississippi and Texas (College Station). At these three locations the untreated check gave the highest yield. The high-soil-K treatment. The low-soil-K-plus-foliar-K treatment tended to increase yield the most (by 200 lb/acre compared to the untreated check, and by 50 lb/acre compared to the low-soil-K treatment). Strangely, the high-soil-K-plus-foliar-K treatment, and by 60 lb/acre compared to the low-soil-K-plus-foliar-K treatment.

The effect of potassium treatment on boll number and boll weight showed no clear trends. Periole and leaf blade K concentrations declined during the sampling period. The periole K concentrations were high at the beginning of the sampling period (±5.5%) two weeks after flowering and declined to (±1%) eight weeks after flowering, wheras the leaf blade K concentrations were much lower (±2%) and only declined slightly during the same period. Analysis of petioles rather than leaf blades may provide K concentrations although some variation was experienced. The results of the fiber analyses are not yet available.

This study will be repeated again in 1992 with the inclusion of an addition six locations. While firm conclusion cannot be drawn on the one year's data, foliar application of KNO₃ appears to offer some potential for supplementing preplant soil application of potassium fertilizer, but only when soil or petiole analyses show a low potassium status. Additional research is required at both applied and basic levels.