بررسی تأثیر شکل های مختلف نیتروژن و pH محیط ریشه بر رشد گراس Brachiaria brizantha در کشت هایدروپونیک

This study was conducted to evaluate plant response of Brachiaria brizantha cv. MG5 to nitrogen (N) forms and different pH's of nutrient solution. In this study, under controlled conditions in growth chamber with hydroponics culture, seedlings after germination were treated with different N forms as nitrate, ammonium, and ammonium nitrate, as well as with different nutrient solution pH's. A solution of 5 mM morpholinoethanesulfonic acid (MES), or/and calcium hydroxide or/and calcium carbonate were used for pH adjustment. Nutrient solution containing ammonium and ammonium nitrate were fixed at pH 4, 6 or 8, and nutrient solution containing nitrate was fixed at pH 6. In another experiment seedlings of Brachiaria were grown in nutrient solution with different N forms, but without pH adjustment. The results showed that plants grown in ammonium or ammonium nitrate at pH 4 had better growth and plant performance, followed by pH 6, compared to plants grown at pH 8 (buffered with calcium carbonate). The presence of calcium (bicarbonate) in nutrient solution significantly reduced plant growth, particularly root growth and development. It seems that the negative effect of carbonate at high pH was higher than low pH. High concentration of carbonate in presence of ammonium was also toxic for plants. However plants were able to grow normally with different N forms under hydroponics culture, independent of pH effect. In this case, there was no significant difference between root and shoot biomass production at 5% of probability level. So the presence of carbonate but not pH, determined as an inhibiting factor for growth of B. brizantha cv. MG5 seedlings.