Nitrate and ammonium as nitrogen sources for lupins prior to nodulation

Abstract

A b s t r a c t • H +Two cultivars of Lupinus angustifolius L. were grown in a glasshouse in solutions containing N O ; , N 4 o r N H 4 N O 3 with a total nitrogen concentration of 2.8 M m -3 in each treatment. One cultivar chosen (75A-258) was relatively tolerant to alkaline soils whereas the other (Yandee) was intolerant to alkalinity. Controlled experiments were used to assess the impact of cationic vs. anionic forms of nitrogen on the relative performance of these cultivars. Relative growth rates (dry weight basis) were not significantly different between the two cultivars when grown in the presence of NO~, NH 4 or N H 4 N O 3. However, when NO 3 was supplied, there was a modest decline in relative growth rates in both cultivars over time. When plants grown on the three sources of nitrogen for 9 days were subsequently supplied w i t h 15NHnNO 3 o r NH145NO3 for 30 h, NH2 uptake was generally twice as fast as NO 3 uptake, even for plants grown in the presence of NO 3. Low rates of NO 3 uptake accounted for the decrease in growth rates over time when plants were grown in the presence of NO 3 . It is concluded that the more rapid growth of 75A-258 than Yandee in alkaline conditions was not due to preferential uptake of NH 4 and acidification of the external medium. In support of this view, acidification of the root medium was not significantly different between cultivars when NH 4 was the sole nitrogen source.

Nutrient Uptake and Organic Acid Anion Metabolism in Lupins and Peas Supplied with Nitrate

“…unaffected. Similar Similar results results were were obtained obtained by by Atwell Atwell (1992), (1992, who who found found that that the the pH pH of of the the nutrient nutrient MATERIALS MATERIALS AND AND METHODS METHODS solution solution did did not not increase increase when when lupins lupins were were supplied supplied with with Experiment Experiment 1 1 NO;. NO;.…”

“…Kerven et al (1991) also did not achieve complete sterility when plants were grown in 30 mg 1-1 cefotaxime, however they did not measure any significant loss of organic acids from their system due to microbial decomposition. It might be expected that the micro-organisms will break down the organic anions to OH-and CO" however there was no increase in the pH of the nutrient solution in these and other experiments (Atwell, 1992;Loss et al, 1993b). Micro organisms may convert the organic anions into microbial biomass containing carboxylate groups that do not affect the pH of the external nutrient solution.…”