ABSTRACT

The increased cost of cotton (Gossypium hirsutum L.) production paired with low commodity prices necessitates more efficient nutrient management for the crop. The ability to monitor nitrogen (N) and potassium (K) levels throughout the growing season allowing detected deficiencies to be corrected on a timely bases improves the possibility of achieving optimal yields. Petiole analysis is available to the producer from university and independent labs as a tool to monitor crop nutrient levels during the growing season. A common problem of traditional lab analysis is the lack of timely results to the crop advisor.

Sampling and conducting the petiole analysis the same day can eliminate this time lag. One method of same day analyses is the utilizing of Cardy portable electrode-based ion meters (Horiba, Ltd., Kyoto, Japan). The Cardy NO3-N and K ion meters offer crop advisors the ability to quickly evaluate crop N and K levels relative to growing conditions. Cardy meters have been widely used in vegetable production with NO3-N and K thresholds established for several crops (Maynard and Hochmuth, 1997). During the past decade several researchers (Burmester and Mullins, 1994; Hodges and Baker, 1993; and Smith, et al. 1997) have investigated the utility of Cardy meters as diagnostic tools in cotton.

Hodges and Baker (1993) found that routine lab analysis and the Cardy meter measurements were strongly correlated (r=0.88) although a change in the slope of the correlation equation was noted with increasing time. A major problem in the correlation process is the extraction of petiole sap after bloom. Because of this, these researchers suggested that the meters would be useful for early season measurements and for evaluating problem areas in fields. Burmester and Mullins (1994) obtained similar results when evaluating the K meter for in-field measurements. Contradictory to the earlier study the K correlations between lab analysis and Cardy meter were poor (R2=0.08 or less) in all but the bloom sampling period (R2=0.53). These poor correlations were attributed to the difficulty in obtaining sap extract as the plant matured. Burmester and Mullins concluded that the best use for the Cardy meters would be early season before the petioles hardened.

As with any diagnostic tool there are potential problems associated with the Cardy meter. In addition to improper calibration, environmental conditions, and maintenance issues Hodges and Baker (1993) found the meters to be highly sensitive to high temperature and sunlight. Smith, et al. (1997) conducted a trial to analyze the accuracy of the Cardy meter to effectively measure NO3-N in irrigated cotton. As with previous correlation experiments, petioles were randomly sampled and divided into two samples, one for Cardy meter analysis and one for the standard lab analysis. Correlation and linear regression analysis were conducted on NO3-N concentrations as measured by the Cardy Meter versus the standard lab analysis. The two NO3-N petiole analysis methods were highly correlated (Pearson correlation coefficient = 0.96, P<0.0001) throughout the growing season. A highly significant (P< 0.0001) linear regression equation was derived: Y = 9.96X - 1170.86 (n = 279, R2=0.92), where X and Y are NO3-N concentrations (ppm) for Cardy meters and standard lab analysis, respectively. Their results suggest that the Cardy meters can be a valuable diagnostic tool to monitor NO3-N levels in cotton.

This study was continued to evaluate the NO3-N and K Cardy meters as an in-field diagnostic tool for cotton production. The study was conducted in several locations across the cotton belt. The Cardy meter N and K determinations were to be correlated with N and K values determined by the University of Arkansas lab at Marianna, AR.