Abstract

A two year field experiment was conducted to determine the residual effects of different organic and inorganic sources of nitrogen on the succeeding ratoon crop of rice (cv.IR 36). Eighteen treatments consisting of five green manure crops viz. Azolla (Azolla pinnata R.Brown): Ipomoea (Ipomoea carnea) water hyacinth (Eichhornia crassipes Mart Solms) Pistia sp. and blue green algae (BGA) and one farm yard manure (FYM) combination with various rates of inorganic N fertilizer were evaluated. Only 42.0 to 58.0 per cent culms regenerated in ratoon crop from the 50 hills/m² of plant crop. Variation in the grain yields (1.32 to 2.42 ha) of ratoon crop was a consequence of the residual fertility left by the different sources of N applied to the preceding plant crop. Incorporation of Azolla and BGA to the precceding plant crop resulted in higher grain and straw yield of ratoon crop. Concentration of N,P and K in grain and straw of ratoon rice was higher in the treatments having higher fertility. Residual status of N.P and K in the soil after ratooning declined compared with initial values.

Keywords: Plant crop, ratoon crop, residual fertility