Abstract
The results of two sets of soil nitrate measurements on the three-course rotation plots at the Gezira Research Farm are described. The first set is a long-continued series taken over 21 years; it shows for the first foot samples that there is a distinct tendency for nitrates to be depressed during the rainy season, this tendency being more marked in the more open rotations. This is ascribed to washing down of nitrates. The second set of measurements shows accumulations in the second foot and a distribution consistent with downward movement.In the Sudan Gezira the yields of irrigated cotton are positively correlated with the amount of rainfall in the 6 weeks before sowing. It follows from the work described here that this is not due to increased nitrate in the top foot of soil at sowing time.The sampling of this experiment for nitrate was started by my predecessor, H. Greene, and continued by O. W. Snow. The field experiment itself has been conducted by the Plant Physiology Section of the Research Division of the Ministry of Agriculture.
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