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Line-Source Sprinkler Systems for Experimentation with Sprinkler-Applied Nitrogen Fertilizers¹

ABSTRACT

A triple line-source system was developed and evaluated as an alternative field plot design that allows superimposition of a continuous gradient of sprinkler-applied N within uniform sprinkler irrigation. Two outer laterals are used to apply water only while a third lateral centered between the outer laterals is used to apply water plus injected N fertilizer. This layout provides duplication of the N gradient on each side of the center lateral. Equality of slopes and intercepts of linear regressions individually fit on both sides of the center lateral indicates good duplication and symmetry of the N gradient about the center lateral. The main disadvantage of the technique is the potential statistical bias stemming from the nonrandom treatment arrangement. Having good symmetry of response variables across the N source line indicates lack of statistical bias associated with nonrandom treatments because of the low probability that unknown gradients coincident with the N gradient would exist at the same magnitude at 180 degrees to each other. The technique is probably best suited for single independent variable investigations which exhibit large treatment differences relative to potential bias. In using this or any other continuous variable designs, the main inherent disadvantage of nonrandom treatment arrangement must be balanced against the main inherent advantages of smaller plot areas associated with the elimination of border areas and considerable savings of other research resources.

¹ Contribution from the USDA, Agricultural Research Service, in cooperation with the College of Agriculture Research, Washington State University, Pullman. Scientific Paper no. 6141 of the latter.

² Research Soil Scientist, USDA-ARS, Prosser, WA 99350.

Received for publication March 4, 1982. Accepted for publication September 23, 1982.