Effects of Soil Moisture in the Summer and Autumn on the Contents of Nitrogen Compounds in Satsuma Mandarin Fruit

Abstract

A study was made in the summer and autumn of 1976 on the effects of different soil moisture conditions on the contents of nitrogen compounds on the quality of Satsuma mandarin fruit.The following results were obtained:1) Fruit of high quality was obtained from trees grown under medium moisture (pF 2.0-2.5) in August and under low moisture (pF 3.0-3.5) in September. The contents of soluble solids in the juice of the fruit, the water content of the pulp and weight of the fruit were affected more by low moisture in September than they were in August.2) The proportion of alcohol insoluble solids in the pulp decreased under reduced soil moisture. This suggests that hydrolysis of polysaccharides may occur and that this produces the high sugar content in the juice when there is low moisture.3) Contents of the total and soluble nitrogen compounds in the peel and in the pulp, as measured on Oct. 4, showed greater increases under low moisture given during August and under medium moisture given during September than they did under other soil moisture conditions. Contents of the total, soluble and insoluble nitrogen compounds in the peel as measured on Dec. 4, were higher under the low moisture regime given in August than they were under the medium moisture regime for the same period.4) The contents (mg per 100 ml juice) of proline, arginine, asparagine, aspartic acid, serine and γ-amino-butyric acid increased more under low moisture than under medium moisture during August and September. High proline and arginine contents (percent based on the dry weight of juice) and a low alanine content were observed under low moisture. Contents of asparagine and aspartic acid, measured on Oct. 4, were higher under the low moisture than under the medium moisture regime given in August. The metabolism of amino acids in mandarin fruit appeared to be altered by the condition of soil moisture during August and September.