The Dualex - a new tool to determine nitrogen sufficiency in broccoli.

摘要

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 sidedressing (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 experimental 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.