Responses of Different Lines of Soybeans (Glycine max L. Merr.) to High Levels of Phosphorus and Potassium Fertility

Comparisons were made of the response to fertilizer of many varieties and Plant Introduction lines of soybeans in field experiments at different locations in Illinois over a 3‐year period. At each experiment one‐half the area within each replication received a large application of P and K and the other half remained untreated. Varieties and lines were then planted in random arrangements in each half of each replication. Yields of each variety and line were measured and observations of some morphological characteristics were made. Results were analyzed to learn whether the different soybeans responded differently to the high level of soil fertility. Some varieties and lines do possess, to a greater degree than others, the ability to respond to high levels of fertility. Other varieties are insensitive to variations in fertility, and yield nearly as well at mediocre fertility levels as on highly fertilized soils. A majority of the lines and varieties tend to respond to a similar degree. “Ability to respond” was usually exhibited consistently though different years. In a few instances varieties appeared to respond differently in different years but the year‐variety interaction was never statistically significant in this study. At one location, ratings of several morphological characteristics (e.g. standability) were made and the effect of fertilizer on these ratings was determined for each genotype. While correlation coefficients between pairs of those effects were low, several were statistically significant and suggested some interesting relationships. For example, varieties that responded more to fertilizer were usually the higher‐yielding varieties. Increases in stem length tended to be associated with increased yield response. Varieties that exhibited the most severe potassium‐deficiency symptoms were not usually the ones that gave the greatest yield response to fertilizer.