ISHS Acta Horticulturae 710: International Symposium on Greenhouses, Environmental Controls and In-house Mechanization for Crop Production in the Tropics and Sub-Tropics
EFFECTS OF NITROGEN FORMS ON THE GROWTH AND IONIC CONTENT OF LOWLAND CAULIFLOWER UNDER TROPICAL GREENHOUSE |
| Authors: | A. Ahmad, S. Mohd, M.R. Ismail, M.K. Yusop, M. Mahmood |
| Keywords: | lowland cauliflower, curd yield, NO3-N, NH4-N, NH4NO3, cations, anions |
| Abstract:
An experiment was conducted to determine the effect of different N forms on the growth and mineral contents of lowland cauliflower grown on coconut coir dust under tropical greenhouse condition. The plants were fertigated with complete nutrient daily with nitrogen in the form of NO3-N, NH4-N and NH4NO3 at N level of 50 mg l-1. Plant growth was inhibited when NH4+ was supplied as the sole N source. No inhibitory effects were observed when NO3- and NH4+ were applied simultaneously as NH4NO3. It was also shown that NH4NO3 did not result in higher growth and curd yield of cauliflower plants than NO3-N alone. The dry weight of the plants and curd yield was 28.11% and 17.47%, respectively, higher in plants supplied with NO3-N than in plants supplied with NH4NO3. NO3- was not detected in the leaves of plants supplied with NH4-N. These findings suggest that the growth inhibition of plants supplied with NH4-N may be due to the lack of NO3- supply. The pH of the coconut coir dust in which plants were supplied with NH4-N resulted in lowering the medium pH to 3.68 from the initial coconut coir dust medium pH of 5.30. The consequence of this acidification was that plant cations (K+, Ca2+, Mg2+ and Zn2+) uptake was 40% to 70% reduced. In contrast, the anion concentration of P was significantly higher in the leaf of NH4-N (1.35% dry weight) than in both NO3-N (0.79% dry weight) and NH4NO3 (0.77 % dry weight) grown plants. The results in this study suggest that lowland cauliflower essentially grows at 50 mg l-1 N on the coconut coir dust medium with NO3- as a sole N form. | |
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