In order to develop a better understanding of some yield components, the response of three modern cotton (Gossypium hirsutum L.) cultivars to increasing nitrogen (N) fertiliser application was assessed for lint percentage (LP) and seed weight, as well as seed protein and oil concentrations. Application of N fertiliser led to decreased LP in all three cultivars (by 1.5 percentage points), even if the N-fertiliser rate was above the optimum rate. There was a strong negative correlation between LP and seed mass because seed mass is a component of LP. Seed protein concentration increased, and seed oil concentration decreased, with increasing N fertiliser application. Seed germination was improved in seeds with higher oil concentration; therefore, seed produced with high N fertiliser had reduced seed vigour. It was concluded that little scope exists for further lint-yield increase via LP. For cultivars with small seeds, an integrated system across seed production and crop agronomy can achieve satisfactory seed vigour in the field while also achieving high commercial yields. Future improvements in yield will come from alternative and more complex yield components such as growth habit.