N uptake and recovery by onions from peat-mineral fertilizers
Nitrogen release from peat-ammonia-mineral fertilizers (PAMF) could be partly controlled by granule size and soil application of nitrification inhibitors. The objective of this study was to evaluate the effects of various combinations of nitrapyrin, a nitrification inhibitor, and granule sizes of PAMF on onion (Allium cepa L. ’Norstar 210B’) yield and N recovery. The study was conducted in a growth chamber, with two soils, two nitrapyrin rates (0 and 8 mg kg−1), three PAMF rates (0, 133 and 266 mg N kg−1) and three granule sizes (2-, 4- and 10-mm diameters). Nitrogen-use efficiency was assessed using the 15N technique. Nitrapyrin considerably depressed onion yield and failed to improve PAMF efficiency because of apparent ammonia toxicity. The 10-mm granules produced higher dry matter yield (3–8%) and root length (1–9%) than 2-mm and 4-mm granules. Maximum N recovery from PAMF 10-mm granules reached 47% in the Tilly soil and 76% in the Chaloupe soil. In contrast to nitrapyrin, granule size may improve N availability to onions from PAMF. Key words: Ammonia, fertilizers, 15N isotope, nitrapyrin, N recovery, onions, peat