Analysis of crop-rotation experiments, with application to the Iowa Carrington-Clyde rotation-fertility experiments
This report presents a model by which several crop rotations are compared, and optimal fertilization and rotation practices determined. The model is developed with specific applicability to the rotation- fertility experiments at the Carrington-Clyde Experimental Farm near Independence, Iowa. The substitutability of legume meadow and chemical nitrogen fertilizer and the effect of carry-over of applied nitrogen from crop to crop are incorporated into the analysis. The split-plot nature of the rotation- fertility trials is noted, and a transformation of the yield data is employed to create nearly uncorrelated observations. Response functions are estimated for each crop in each rotation. Optimal fertilizer rates and rotations Eire determined on the basis of average annual return. Variance of return arising from yield variability over years is estimated. Continuous corn yielded the largest net income for the prices considered in the study. The net income per acre decreased with the introduction of oats and an increasing number of years of meadow. Variability of annual net return, however, was largest with continuous corn and decreased as the number of years of meadow in the rotations increased.