RICE RATOONING - IRRI books - International Rice Research Institute

100 RICE RATOONINGthe results of pot experiments because in all the treatments, Azolla was applied to themain crop. We stopped applying Azolla to the ratoon crops with zero N and50 kg N/ha treatments. During the autumn-winter months when the main crop wasgrown, the temperatures were favorable for the multiplication and development ofAzolla. Probably, the decomposition of Azolla resulted in green and vigorousratoon plants in all the pots. Even in those pots where Azolla was maintained in theratoon crop, the multiplication of Azolla slowed in March when the temperaturesstarted rising. Hence, application of Azolla to the ratoon crop in this region may notbe beneficial.We did field insecticidal trials with a ratoon crop of Sona Mahsuri. We usedfour fertilizer treatments and two insecticides with a control. The treatments aresummarized in Appendix 1.Azolla could not be uniformly maintained in the field because of fluctuatingwater level and snail damage. The higher temperatures during the ratoon cropseason may also be the reason for its poorer development and multiplicationparticularly in March-April. Soil salinity (pH = 8.3) may be another reason. The 50kg N/ha treatment gave the most regenerated tillers/plant and the highest ratoonyields. The ratoon tillers were vigorous and green, and exhibited delayed flowering.Tillering was poor in the control and better in plots treated with Azolla only(Table 2).Applying Azolla immediately after ratooning may not benefit the ratoon cropbecause Azolla N is not available to the plants until the Azolla decomposes. In thepot experiment, Azolla N was continuously available to the ratoon crop treated withAzolla only. This partially explains inconsistencies between pot and field experiments,but more experiments are required for conclusive results.Insecticide - nitrogen source interactionThere was no significant interaction between nitrogen source and insecticideapplication in relation to ratoon growth and development because there was no pestpressure in either crop. In the summer crop of Sona Mahsuri grown in farmers’fields, we observed BPH incidence. The canopy of the ratoon Sona Mahsuri crop inour experiment was not as thick as the farmers’ crop.There was significant variation in number of regenerated tillers, shoot androot weight, panicles/plant, and yield. Mineral nitrogen at 50 kg/ha gave the highestmean yield, 2.02 t/ha, in Sona Mahsuri (Table 2).Application of chemical herbicidesIn one herbicide experiment, chemical weedicides were applied to main and ratooncrops of Tellahamsa. Six weedicides were used at three concentrations, along withan unweeded check plot. The other two treatments were hand weeding twice duringthe crop growth and maintaining the plot weed-free. The treatment was repeated 1wk after ratooning (Appendix 2). Rice seedlings germinated from the fallen grainsand competed with the ratoon crop as weeds. Hand weeding was the most effectiveweed control method in the main and ratoon crops. Among weedicides, however,pendimethalin at all three concentrations checked weeds in both crops. Ratoon