Comparison of two methods for the analysis of petiole nitrate nitrogen concentration in irrigated cotton

A study was conducted in Arizona in 1997 with the objective of analyzing the accuracy of a recently developed portable nitrate meter (Cardy meter) to effectively measure nitrate-nitrogen (NO₃-N) in irrigated cotton (Gossypium ssp.). This task was accomplished by performing a correlation and linear regression analyses on NO₃-N concentrations of cotton petiole sap, as measured by the Cardy meter, against the standard procedure using dried petiole NO₃-N concentrations, as measured by the ion selective electrode (ISE). Results revealed that the NO₃-N concentrations of petiole sap were highly correlated with dried petiole NO₃-N (pearson correlation coefficient = 0.96, P <0.0001). Therefore, a regression equation with an r² = 0.92 was derived: Y = 9.96X - 1170.86, where X and Y are NO₃-N in petiole sap (ppm) and dried petiole (ppm), respectively. These results suggest that the sap analysis using the Cardy meter is a potentially valuable tool to monitor the in-season N status of irrigated cotton.