To evaluate residual effects of potassium fertilization throught ryegrass on subsequent rice, under no-tillage system, a field experiment was performed from May 1996 to April 1997 in the Agricultural Center (Centro Agropecuário) of Palma/UFPel, in the county of Capão do Leão, Rio Grande do Sul State, Brazil. The examined soil was a Planossolo (Albaqualf) belonging to the Pelotas mapping unit. Treatments consisted of three K levels applied on the ryegrass (0, 0.5 and 1 time the recommended dose of 70 kg ha-1 K2O) and four K levels on the rice grown after the ryegrass (equivalents to 0, 0.5, 1 and 1.5 times the recommended dose of 60 kg ha-1 K2O), resulting in complete factorial of twelve treatments. The design used was a randomized block with three replicates. The results indicated that: (a) the available K after the cultures does not increase in this soil with potassium fertilization in the recommended dosages; (b) the ryegrass potassium fertilization residual effect to the following culture, in this soil, is equivalent, at least, to 56 % of the applied potassium contained in the aerial part of ryegrass.
rice; ryegrass; potassium; no-tillage; crop rotation