Möjligheter att förutsäga kvävegödslingsbehov i höstvete med Yara N-tester

Abstract: The Yara N-Tester is a handheld chlorophyll meter which can be used in several different crops as an aid to determine if there is a need of complementary fertilization with nitrogen (N) or not. If the crop requires more N the N-Tester will recommend an amount in kg per ha. The possibility to assess the need of N depends on the strong relation that exists between chlorophyll- and N-concentration in the leaves of plants. In the multiannual trial series “Nitrogen to winter wheat at different soil conditions” measurements with the N-Tester was carried out at flag leaf emergence (GS 37). In this work the result of measurements, the NTesters ability to estimate the need of N in winter wheat, will be presented for the years 2008-2011. The relation between the measurement value and the actual need of N is highly affected by current weather such as temperature and precipitation and the strongest correlation value was found in year 2010 (r2=0.68) and the weakest in 2011 (r2=0.26). When the recommendations differ from the actual need they are often too high. In addition to the compilation of field trial data farmers and advisers have been interviewed. The questionnaire was about the N-Tester as a tool and its reliability when it comes to estimating the need of N in winter wheat. Generally interviewed farmers are satisfied with the N-Tester even though some find it to overestimate the N-need. Advisers’ attitudes are more negative and many question the relation between measurement value and actual N-need.