ISHS Acta Horticulturae 533: VIII International Symposium on Timing Field Production in Vegetable Crops
INFLUENCE OF SOME AGRONOMICAL PRACTICES ON QUALITATIVE AND YIELD TRAITS OF LETTUCE HEADS |
| Authors: | V. Miccolis, V. Candido, G. Posca |
| Keywords: | nitrogen source, harvesting time, transplanting dates, lettuce cultivars |
| Abstract:
A trial for ascertaining the influence of cultivation period, nitrogen source after transplanting and harvesting time on performance, yield and nitrate content of heads was carried out on different cultivars of Lactuca sativa L. in Scanzano Jonico, a horticultural area of Basilicata region (40°20'N and 16°48'E), in 1995–'96. A split-plot design with 4 replications was followed using 8 lettuce cultivars (‘Tenerife’, ‘Verian’, ‘Lorka’, ‘Coolgard’, ‘Manavert’, ‘Valmaine’, ‘Sigla’ and ‘Terra’) in three different cultivation cycles, i.e. in autumn and winter 1995 as well as in spring 1996. The same fertilization was used before transplanting, i.e. 33, 100 and 45 units of N, P2O5 and K2O ha-1, respectively. After transplanting other 99 N units ha-1 were applied in three different chemical forms, i.e. nitric, ureic and ammonical, in three sub-rates of 33 N units ha-1 at the following times: one week after transplanting, at 6–7 leaves stage and just before head closure. Harvesting was performed at marketing maturation and 10 days later. Dry matter and nitrate and nitrose content were determined on representative samples of each cultivar and fertilization schedule. The results obtained showed that cultivation season markedly influenced cultivar yield and nitrate content of lettuce heads. In particular, nitrate mean content reached 562 mg Kg-1 of fresh matter (f.m.) in heads produced at the end of winter 1995 and spring 1996 but increased up to 995 mg Kg-1 of f.m. in heads obtained at winter beginning. Nitrate average content was 760 and 598 mg Kg-1 of f.m., in lettuce heads obtained from plant cultivated in soil fertilized with nitric or ureic N form and, with ammonical one, respectively. Independently on the N source used after transplanting, some of the tested cultivars showed high yield differences ranging from a min of 8 and a max of 20 t ha-1. Nitrate content was high (1212 mg Kg-1 of f.m.) in heads of ‘Sigla’ and ‘Terra’ cultivars, whereas reached 705 mg Kg-1 of f.m. in ‘Tenerife’ and ‘Verian’, and 454 mg Kg-1 in all the others. Delayed harvesting lowered the mean nitrate content of the fresh product from 787 to 625 mg Kg-1 in all tested cultivars except for ‘Valmaine’ in which this parameter increased of about 9 % in heads collected 10 days after commercial ripening. | |
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