THE DUALEX A NEW TOOL TO DETERMINE NITROGEN SUFFICIENCY IN BROCCOLI
Commercial production of broccoli is highly dependent on nitrogen (N) fertilization. With high amounts of precipitation or irrigation, leaching of N below the root zone may constitute an environmental risk, especially when available soil N exceeds plant uptake, which is often the case early in the season. The recommendation in Quebec is a split application of 85 kg N/ha at transplanting and 50 kg/ha at side¬dressing (four to five weeks later). The sidedressing application can be adjusted based on a prior test of N sufficiency. The aim of this study was to determine the effect of N rate and irrigation on the sensitivity of different tests, including the Dualex, a new instrument measuring the status of leaf polyphenolics (Phen). Experimental fields were established in 2005 and 2006 at the Agriculture and Agri-Food Canada experi¬mental farm of L'Acadie (Quebec). The crop was fertilized with 0, 105, 135, 165, 195, or 225 kg N/ha and provided, or not, with supplementary irrigation after crop establishment. Sap NO3, leaf epidermis Phen, and chlorophyll contents (Chl) were determined periodically using the Nitrachek reflectometer, the Dualex, and the SPAD-502 chlorophyll meter (chlmeter) respectively. Yields of marketable heads increased in a curvilinear matter with N rate, with a tendency to plateau at high rates. There was low mineral N available in the soil at harvest, regardless of irrigation, but the level was linearly related to N rate. Dualex readings were generally not affected by irrigation and quick to react to N application, generally in a linear manner. They compared well to both the sap test and the SPAD meter. The ratio of chlorophyll meter to Dualex readings (Chl/Phen) was particularly sensitive to seasonal N requirements.
Tremblay, N., Bélec, C., Jenni, S., Fortier, E. and Mellgren, R. (2009). THE DUALEX A NEW TOOL TO DETERMINE NITROGEN SUFFICIENCY IN BROCCOLI. Acta Hortic. 824, 121-132
chlorophyll meter, sap test, Nitrachek, reference plot, polyphenolics