Establishment of Continuous Critical Levels for Indices of Plant and Presidedress Soil Nitrogen Status in the Potato Crop
2004; Taylor & Francis; Volume: 35; Issue: 13-14 Linguagem: Inglês
10.1081/lcss-200026837
ISSN1532-2416
Autores Tópico(s)Plant nutrient uptake and metabolism
ResumoAbstract Critical levels for six plant and presidedress soil nitrogen (N) indices were established for the growing season, and their relative accuracy to diagnose the need for supplemental sidedress N was also compared. Field trials were conducted from 1996 to 1998 with irrigated potato in northeastern Portugal. Fertilizer treatments included several preplant and sidedress N rates. Petiole nitrate concentrations (determined by a standard laboratory method and with the portable RQflex reflectometer), leaf N content, leaf greenness (SPAD-502 chlorophyll meter), presidedress soil NO3-N and presidedress soil inorganic-N (NO3-N + NH4-N) were selected as N indicators. The Cate-Nelson graphical method and an analytical procedure using Mitscherlich type curves were used to determine critical levels. In both cases, a yield reduction of 10% was accepted. The accuracy of the diagnostics was estimated from the Cate-Nelson graphical method, quantifying the point percentage that appears in negative quadrants (the error...
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