Effect of irrigation and nitrogen treatments on yield, quality, plant nitrogen uptake and soil nitrogen status and the evaluation of sap test, SPAD chlorophyll meter and Dualex to monitor nitrogen status in broccoli

Abstract: Broccoli (Brassica oleracea L. ssp. italica) is a crop benefiting greatly from nitrogen fertilization and the risk of leaching to groundwater is high. Nine N fertilizer treatments, from 0 to 225 kg N/ha and two irrigation treatments, irrigated and non-irrigated, were arranged in a split-plot design. Nitrogen had a curvilinear effect on marketable yield; an increase was seen up to an application of 165 kg N/ha where the response plateaued. Hollow stem was the only disorder related to N application noticed in this project. It was seen only in treatments receiving more than 165 kg N/ha and the number of heads affected was very low. Plant uptake of N was strongly affected by nitrogen application and a large effect from irrigation was observed at harvest. The difference could only be explained by leaching early in the season and denitrification during the season. The risk of leaching early in the season is critical when the amount of precipitation and/or irrigation is above field capacity. Sap test, SPAD chlorophyll meter and Dualex were compared as a way to monitor nitrogen status. Sap test was the method showing the largest effect among different N applications but also the largest variability. The SPAD chlorophyll meter was very sensitive to differences in nitrogen application, even though it had the narrowest span from high to low fertilized plants. The Dualex showed the best relationship with plant nitrogen uptake. It quickly showed differences among N application and a good correlation with yield. The use of a reference plot is recommended to decrease the influence of factors other than N affecting test results and to obtain relative values that can be used in different conditions.