Tradeoff study on N nutrition status assess approaches of cotton

Field and greenhouse experiments were conducted at the Arkansas Agricultural Research and Extension Center in Fayetteville with the objective of comparing conventional leaf-blade and petiole N combustion methods with SPAD meter ( Minolta Chlorophyll Meter ) and Cardy meter (Horiba, Ltd., Kyoto, Japan) to assess and monitor the nitrogen status at bloom stage of cotton. The layout of field trial was a split-split-plot design with six replications. The main plots consisted of soil fertilizer N levels, high N (HN) and low N (LN), the sub plots were high (HB) and low (LB) boll load, and the sub-sub-plots consisted of foliar and no-foliar N applications. Tissue samples were collected with a week(7 days) interval starting from a week after first flower and keeping for five weeks. Correlation analyses was used to compare chlorophyll meter readings, measured with the SPAD meter with the leaf-blade N concentration, measured using the traditional laboratory analytical method as well as NO3--N concentrations of cotton petiole sap, measured by the Cardy meter, and traditional laboratory analytical method respectively. This study showed that chlorophyll meter readings measured with the SPAD meter and Cardy meter reading were significantly correlated with leaf-blade N concentration and petiole NO3--N. The reading of these approaches indicated N content in leaf-blade and leaf stem varying along with the change of N addressing rate, boll load and foliar fertilizer applied at anaphase stage. At high N addressing rate, N content in leaf blade and leaf stem of the cotton with low ball load or foliar fertilizer application was significantly higher than others. The results also showed that the hand-held chlorophyll meter and Cardy meter might be as reliable as leaf-blade N and petiole NO3--N for the purpose of supplemental N fertilizer requirements predication of cotton. They were promising valuable tools to monitor the in-season N status of irrigated cotton in Arkansas. Further field comparisons of these methods under different environmental conditions, i.e. drought, should be carried out in the future.