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Field nitrates in the Gezira soil. II

Published online by Cambridge University Press:  27 March 2009

T. N. Jewitt
T. N. Jewitt
Affiliation:
Research Division, Ministry of Agriculture, Sudan
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Extract

The yields of cotton from five three-course rotations are given; they show marked seasonal variations, the variations of the different rotations being in close accord with one another. The average yields of the rotations are related fairly closely to the average soil nitrates; in individual years this is not so, though considerable responses to nitrogenous manuring are always obtained on Gezira soil.

The distribution of nitrate in Gezira soil shows an unusual accumulation at depth; though cotton roots can reach the zone of accumulation, the variability of nitrate at these depths renders it impossible to relate changes to uptake. The figures show that under growing cotton the whole of the upper 4 ft. of soil can have low nitrates (of the order of 1 p.p.m.). Unless the roots obtain nitrate from the fifth and sixth feet accumulations the plants must be taking up nitrate as fast as it is formed, and the nitrate-supplying power of the soil must be of first importance. Figures are given showing differences in nitrification in soil from the different rotations.

The effect of heavy nitrogenous manuring on soil nitrate is shown to be largely confined to the year of application, and no accumulations could be demonstrated. The average recovery of added nitrogen in this experiment is only of the order of 10%. The yields of the heavily manured treatments show the same violent fluctuations as do the unmanured treatments.

In the three-course rotation experiment surface nitrates in August and September in the wider rotations are strongly negatively correlated with the rainfall of the period 1 July to 15 August. Over the period July to September the distribution of nitrates in the upper 2 ft. of the profile changes; there are differences between the rotations in this respect.

Type
Research Article
Information
The Journal of Agricultural Science , Volume 47 , Issue 4 , August 1956 , pp. 461 - 467
Copyright
Copyright © Cambridge University Press 1956

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References

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