Rate and timing of potassium fertilization and fungicide influence rice yield and stem rot

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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.

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