Economic control of fertilizer in highly productive pastoral systems. II. Designing field trials with physiologically balanced fertilizer through subtractive pot experiments

Deficiencies in essential chemical elements were diagnosed for two soils in a pot trial, using a subtractive technique and two different test plants: perennial ryegrass for ‘major’ elements and white clover for ‘minor’ elements. This information was required in a pastoral area to permit field trials to be designed with a suitably fortified superphosphate as the fertilizer input. The trials themselves are wanted to provide economic advice soundly based in relation to nutritional needs of pasture plants and grazing animals. Accordingly, a complex argument has been developed to justify using simple 3-level trials with physiologically balanced fertilizer instead of conventional multilevel factorial types; also to show how the simple trials should be designed.