Under P deficiency amino acids in the root exudates increased from 104.5 to 248.5 umol/plant, which contrasted sharply with the almost 4-fold decrease under N deficiency (104.5-25.1 zmol/ plant; 1). Graham et al. (5) observed P deficiency to result in a 3-fold increase in amino acid exudation with only a concentration increase of 60% within the root.The effective study of the rhizosphere has been limited in the past due to the difficulty of isolating root effects from general soil and microbiological effects and quantifying those effects. The objective of this research was to identify and measure the effect of P deficiency upon the exudation of organic acids by the growing aseptic roots of alfalfa (Medicago sativa L.) seedlings.
Changes in pe and pH of alfalfa (Medicago sativa L.] rhizospheres may be important considerations in the description of nodulation and nutrient uptake. Growth chamber studies were done where alfalfa seedlings were grown into a Sharon sandy loam soil and in situ measurements of pH and pe in zones 0 to 0.5, 0.5 to 1, and 1 to 3 mm from root surfaces made. The pe of the soil 0 to 0.5 mm from lateral and main roots was 7.8 ± 0.05 and was the same as that of the soil at greater distances. The pH in the zone 0 to 0.5 mm from lateral roots was 4.2 ± 0.3, in the same zone near main roots 6.8 ± 0.4, and at distances greater than 3 mm it was 5.54 ± 0.9.
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