Rate and Timing of Potassium Fertilization and Fungicide Influence Rice Yield and Stem Rot

Potassium deficient rice (Oryza sativa L.) is susceptible to diseases including stem rot (Sclerotium oryzae Catt.). Knowledge of how to manage K deficiency and the increased disease susceptibility is necessary to reduce rice yield losses. Our objectives were to determine the influence of K rate, application time, and azoxystrobin fungicide on grain yield and stem rot index (SRI) of rice grown on soils with low K availability. Muriate of potash was applied at 0, 56, and 112 kg K ha(-1) to rice preflood (PF), panicle differentiation (PD), or the late boot (LB) stage. Azoxystrobin fungicide was applied at 0 and 0.23 kg a.i. ha(-1) following the PD K application. Stem rot was assessed at maturity and expressed as SRI on a 1-to-5 scale, with 1 indicating no disease symptoms (healthy) and 5 being a dead culm. Potassium fertilization increased grain yield by 8 to 11% above rice receiving no K. Within each K application time, grain yield of rice receiving 0.23 kg ha(-1) azoxystrobin was 6 to 12% greater than rice receiving no azoxystrobin. Within each azoxystrobin rate, rice yields were lowest when no K was applied, intermediate for K applied at LB, and greatest for K applied PF or PD. The average SRI was reduced significantly by K fertilization and azoxystrobin application. Potassium fertilizer applied between PD and LB can reduce yield losses from K deficiency. Sufficient K fertilizer should be applied PF to prevent potential yield losses from K deficiency and minimize stem rot incidence and severity.