When planting soybeans in Kansas, it may be a good insurance policy to inoculate the seed. Inoculation promotes good nodulation, improves nitrogen fixation, and helps ensure a stable yield. Yield response to inoculants can depend on residual soil nitrogen, soil pH, environmental conditions, and other factors.
If soybean plants are chlorotic and nitrogen deficient despite being inoculated, that probably indicates the inoculant has failed. This article discusses how to assess nodulation in the field and what factors can lead to poor nodulation.