Yield improvement in modern cotton (Gossypium hirsutum L.) varieties has become stagnant in recent years, resulting in a plateau that cotton yields have not been able to break through. Speculation has arisen that a buildup of reniform nematodes (Rotylenchulus reniformis) has occurred during the past decade or more in fields growing continuous cotton and could be contributing to the yield stagnation. Previous research has indicated that cotton grown under insufficient K was more susceptible to root-knot nematode (Meloidogyne incognita) gall formation than cotton grown with adequate K. Therefore the objectives of this study were to assess the susceptibility of various cotton genotypes to reniform nematodes, and to determine if K fertilization altered the native reniform nematode population levels.