Development of a quicktest kit method to measure soil nitrate

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Abstract
A soil nitrate test taken about 4 weeks after emergence has been proposed to predict the corn (Zea mays L.) yield reponse to sidedress N fertilizer applications. Use of this test would be increased if the soil analysis and interpretation could be done rapidly, since the fertilizer must be applied within one to two weeks after sampling. Because of this time constraint, mailing samples to a centralized laboratory is unattractive to many farmers. One potential solution to this problem would be to have the analysis done locally using a quicktest kit. A proposed method for analyzing soil samples for nitrate was adapted for use under field conditions. The method is based on the analysis of soil extracts using nitrate sensitive test strips and a hand held reflectometer. Two soil measuring methods, a conventional scooping method and a weighing procedure using an inexpensive balance, were evaluated for inclusion in the test kit. Evaluation was based on the ability of the methods to measure 20 g of soil. Five extracting solutions including distilled water, 0.01M CaCl2, 0.02M CaCl2, 0.025M Al2(SO4)3, and saturated CaSO4 were also evaluated for use in the kit. Extracting solutions were evaluated on the basis of their effect on strip color development, flocculating properties, potential for preparation of an extracting solution concentrate, and the comparison of quicktest analyses to results from a standard laboratory method. The standard deviation for weighing samples with an inexpensive egg scale was approximately six times less than when samples were taken with a standard 20 g scoop. Standards prepared in the different extracting solutions indicated differences in strip color development existed. Based on solubility and flocculating properties, 0.025M Al2(SO4)3 and 0.02M CaCl2 extracting solutions were selected for comparison to the laboratory method. From this evaluation, 0.025M Al2(SO4)3 was selected for use in the quicktest kit. A list of components of the quicktest kit is included. Use of the quicktest can increase the acceptance of the soil nitrate test for corn, and ultimately improve N use efficiency and minimize nitrate pollution problems.

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