| Potassium is one of the necessary nutrients for crops growth. The growth of rice is restricted by potassium deficiency usually and this phenomenon occurs in the south of China, Fertilizer K application is one of methods to solve this problem. Afield fertilizer K experiment was conducted in jinhua city of China to study the nutrient uptake and internal use efficiency of hybrid and inbred rice (1997-2000, long-term potassium experiment); kinetics of nutrients uptake and utilization of rice in whole growth stage under different K treatments (2002,late rice); N, P, K uptake and utilization of rice and kinetics of soil available N, P, K under different low K stress conditions embedded in a long term site specific fertilizer K experiment (1998-). The main results of studies as below:1. The grain yield increased significantly when K fertilizer was applied at K deficiency soil. In long-term fertilizer K experiment, the average grain yield at fertilizer K treatment was 13.9% and 16.8% higher than that of without fertilizer K treatment in early rice and late rice, respectively. In low K stress experiment of 2002 late rice, the increased scope of grain yield was 12.6% and 19.8% in CK treatment (without fertilizer before) and NP treatment (without K fertilizer before) once K fertilizer was applied. The panicle number per m2, filled speclets number and thousand-grain weight in K fertilizer treatment were higher than that of without K fertilizer treatment. Among them, the contribution of increasing panicle number per m2 to grain yield was higher than the thousand grain weight which did little contribution to grain yield increase.2. Total K uptake and internal K use efficiency changed significantly when fertilizer K was applied. In long-term fertilizer K experiment, total K uptake of rice in treatment with fertilizer K application was 62.3% and 74.8%higher than that of without fertilizer K application in early rice and late rice respectively. However the internal K use efficiency (IEK) in treatment with fertilizer" K application was 32.5% and 29.1% lower than that of the latter respectively. In 2002 late rice experiment, total K uptake of rice increased by 68.9% and 84.2% in CK and NP treatment once fertilizer K was applied, but IEK use efficiency was decreased by 31.3% and 35.9% significantly (p<1%) respectively.3. The effect of fertilizer K application on rice growth depends on the soil potassium supply. The effect of fertilizer K application and internal nutrient use efficiency (IE) on rice can be81evaluated nicely by QUEFTS model. In 2001 late rice experiment, the effect of fertilizer K application was not evident on account of that the IEK was 47 kg kg"1 in treatment without fertilizer K application indicated that soil K supply was sufficient. In 2002 late rice experiment, the effect of fertilizer K application was evident on account of that the IEK was higher than 85 kg kg"1 under low K stress condition. Therefore, IEK 69kg kg"1 which in optimal yield-nutrient uptake curve of QUEFTS model can be used as a critical value to estimate the effect of fertilizer K application in rice field, i.e. if IEK is higher than this critical value, the effect of fertilizer K would be obviously, if IEK is lower than this value, the effect of fertilizer K would not be easily observed in the field. Analysis IE with QUEFTS model, we found that IEN, IEP and IEK was more closer to their optimal value (YN=68 kg kg"1, YP=385 kg kg"1, YK=69 kg kg"1) in treatments with fertilizer K application when compared to the treatments without fertilizer K. Well balanced Fertilizer application management is an effective method to improve internal NPK use efficiency of rice.4. Accumulation of K and IEK was different in different growth stages. The amount of K uptake from panicle initiation to flowering stage occupied 41.2-49.0% of total K uptake in 2001 late rice experiment. The amount of K uptake from panicle initiation to flowering stage occupied 46.5-56.8% of total K uptake in 2002 late rice experiment, while the amou...
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