EFFECTS OF UREA APPLIED WITH ORGANIC MATERIALS ON RICE GROWTH AND ABSORPTION OF NITROGEN

The influence of labeled 15N urea applied respectively with different kinds of organic materials (lignin,cellulose ,starch and rice straw ) on rice growth and nitrogen uptake by rice was studied in a rice pot experiment with soil pre-flooded for 30 days.When urea was applied,1.with lignin,no undesirable rice growth (spike number,straw or panicle dry weight) was observed and the response of rice was not related to the C/N ratios of mixtures) 2.with carbobydrates (cellulose,starch) and rice straw,the retarding effects on rice growth were indeed.Under same C/N ratio conditions,as for these retarding effects,the performance of rice straw was similar to that of cellulose) but the starch presented stronger one than cellulose did although the effects of cellulose plus urea in high C/N ratio were bigger than those in lower C/N ratio.When urea was applied alone,its nitrogen recovered by rice plants or residual in soils were respectively observed as 49.9%or 26.22%.These values were not correspondingly much different with those obtained by mixation of urea and lignin.The addition of other organic materials ,however,would enable urea-N to obtain incerase of its residual in soils and decrease of its recovery by rice plants or losses (except CcN-10:1) although the mixation of rice straw presented the highest urea-N residual (58.8%) in soils,or the lowest value of its recovery (26.8%) and losses (14.4%).In addition,the comparison of organic materials resulted in undesirable urea-N recovery by rice plants was observed as rice straw (C/N ratio 25)>cellulose (C/N ratio 25),starcn (C/N ratio 10)>cellulose (C/N ratio 10).Application of all fertilizers would increase soil-N uptake by rice.When urea was applied alone,437.3mg/pot of soil-N (as 59.5%of total N in rice plants) was absorbed by rice.This value was not significently diferent with those in the treatment of urea plus lignin ,as well as in the urea plus rice straw treatment though its soil-N uptake reached 72.3% of total N in rice plants.Nevertheless,mixation of cellulose or starch would reduce soil-N uptake by rice and increase its proportion of total N in rice plants a little.