Evaluation of soil tests for predicting nitrogen requirements of cereals for some Manitoba soils

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Huang, P. M.
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This investigation was initiated to study the utility of the determination of the accumulated nitrate nitrogen in the soil profile to a depth of four feet at seeding time as a basis for predicting the nitrogen requirements of cereals in Manitoba. Other soil test methods that have been advocated and claimed to be promising were also investigated. The results were obtained from soils of varying profile type, texture, PH, lime and organic matter content. Fertilizer trials were laid out on stubble land using barley as the test crop in 1960 and on stubble and fallow land using oats and wheat as the test crops in 1961. A greenhouse experiment was carried out early in 1961. The accumlated nitrate nitrogen in the soil profile to a depth of four feet at seeding time varied extremely from soil to soil and seemed to be as available as the nitrogen added as fertilizer. The determiniation of accumulated nitrate nitrogen in the profile appeared to have real value in predicting nitrogen needs of cereals for the soils tested in Manitoba... Both the mineralization of nitrogen during the growing season in the fields and that during one-month growth period in the greenhouse seemed to be considerable. The loss of accumulated nitrate nitrogen due to leaching during the growing season seemed to be small. The accumulated nitrate nitrogen in the profile as well as nitrogen fertilizers applied at seeding time appeared to have a bearing on nitrogen taken up and per cent protein in grain. There was evidence that the cereals employed in the 1960 investigation removed accumulated nitrate nitrogen and moisture from the depth of 36-48 inch. It is suggested that if the accumulated nitrate nitrogen of the 0-48 inch depth at seeding time is over 70 pounds per acre, the soil is not suitable for growing Canadian 6-Row barley to be used for brewing purposes. In the 1960 experiment, it was found that there was not much difference between heading stage and harvest time insofar as the accumulated nitrate nitrogen and available moisture in the 0-48 inch depth are concerned. PAN and nitrifying power of the soils tested were similar in magnitude and highly correlated with each other.