ABSTRACT

Raleigh, North Carolina experienced crop failures. At all sites the recommended practices for high yield cotton production for that state were applied. Treatments consisted of (1) no added soil or foliar K, (2) low-soil-K as preplant KCl according to 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 10 lb KNO₃/acre at 2, 4, 6, and 8 weeks after first flower. Whenever KNO₃ was added to the two foliar treatments (4 and 5), 1.38 lb N/acre was added to the other 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 in the upper 6 inches of 159 lb K/acre (California) to a high of 762 lb K/acre (College Station, Texas); the average for the twelve locations was 361 lb K/acre and 258 lb K/acre in the 0-6 and 7-12 inch depths, respectively.

In 1991 the yield results were very variable with significant differences occurred in only three of the twelve locations (Alabama, California, and North Carolina). 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 showed only a slight (non significant) increase in yield of 45 lb/acre compared to the low-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 decreased yield by 10 lb/acre compared to the low-soil-K treatment, and by 60 lb/acre compared to the low-soil-K- plus-foliar-K treatment.

In 1992 significant differences occurred in six of the ten locations (Alabama, Arkansas, California, Georgia, Tennessee, and Mississippi). The low-soil-K and high-soil-K treatments increased yields by an average of 186 and 263 lb lint/acre compared to the untreated control.

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 often be corrected by foliar fertilization with KNO₃. Foliar applications of K may offer the opportunity of correcting these deficiencies quickly and efficiently, especially late in the season when soil application of K may not be effective. While there are many reports on research involving soil applied K, much less is known about the usefulness of foliar-applied KNO₃. The objective of this study, therefore, was to investigate the effect of foliar-applied KNO₃, compared to soil-applied KCI, for alleviating K-deficiency and improving cotton (Gossypium hirsutum L.) yield and fiber quality. This is the second year of this project. The results from the previous year were summarized by Oosterhuis et al. (1992) in the 1992 Beltwide Proceedings.

The trial was planted at twelve sites in 1991 and ten sites in 1992, including Arkansas, Alabama, Arizona, two sites in California, Mississippi, Missouri, Georgia, Tennessee, and Texas. The sites in Lubbock, Texas, and Foliar K applications increased yields by an average of 230 and 332 lb lint/acre compared to the untreated control, and by 44 and 69 lb lint/acre compared to the low soi-K and high-soil-K treatments, respectively.

The effect of K treatment on boll number and boll weight showed no clear significant trends possibly due to the small sample on which these were based. The petiole data is still being analyzed. Petiole and leaf blade (1991 only) K concentrations declined during the sampling period. The effects of the soil- and foliar-K treatments appeared to be reflected in the petiole K concentrations, although some variation was experienced. The results of the fiber analyses are not yet available.

This study will be repeated again in 1993 with a few additional treatments added. While firm conclusions cannot be drawn, foliar application of KNO₃ appears to offer some potential for supplementing preplant soil applications of potassium fertilizer, but only when soil or petiole analyses show a low potassium status. Additional research is required to understand plant K requirements and response to foliar applications.