One problem of farmers is to reorganize the use of their resources as new farming techniques are developed. While not a new technique itself, heavy fertilization of grain crops has not been widespread in Iowa. Recent agronomic research and farmer experience indicate, however, that heavy fertilization rates can be profitable under existing price ratios. Fertilization is a relatively simple practice but it can have complex effects on profitable farm organization.

One of the major impacts of heavy fertilization is on the rotation system. Grasses and legumes grown in rotation can serve in a complementary capacity to grains.2 As complementary crops, grasses and legumes increase profits to the extent that they (1) provide nitrogen to subsequent grain crops, (2) provide organic matter and improve soil tilth, (3) help control insects and diseases and (4) control erosion. Heavy fertilization substitutes for legumes of the rotation in providing nitrogen for subsequent grain crops. It also may substitute for forages in furnishing organic matter. An acre of heavily fertilized corn, for example, can furnish an equal or a greater weight of plant residues than an acre of clover or alfalfa under particular soil and climatic situations such as in north-central Iowa. Under these conditions, the questions arise: What rotation should be used when corn can be fertilized at heavy rates? Are the profit differences small or great from different crop rotations and fertilization rates? Does the optimum combination of rotations and fertilization rates differ between farms of different size which have varying amounts of operating funds and labor?