Effects Of Potassium On Growth Of Rice Under Different Nitrogen Levels

Rice is the most important food crop in China and even in the world. Rice planting area accounts for25%of farmland area in our country, yield of rice accounts for38%of total food yield of our country. Applying fertilizer plays an important part in increasing rice yield, however, in recent years, yield of rice did not increase with the increasing application of nitrogen fertilizer. Excessive nitrogen decreased the economic benefit and increased the risk of environmental pollution. From the view of peasants, unreasonable fertilization and insufficient management are two main reasons limiting yield of rice. Many research showed that nitrogen and potassium are two most important elements for rice. Ratio of N/K2O is1:1-1.5for growth of hybrid rice. Suitable ratio of N/K2O can improve the resistance of rice, build health and high yield group and be benefical to the thanslocation of photosynthetic products from source to base. However, peasants were used to applying the nitrogen and potassium fertilizer at the ratio of1:0.2-0.5. Whether unreasonable applying of nitrogen and potassium fertilizer affects further improvement of rice yield, whether low potassium fertilizer limites the ability of nitrogen fertilizer increasing the yield and how to apply potassium fertilizer to achieve high production and efficiency under the lack of potassium resource situation in our country. Experimental treatments applied in a split plot design, the main treatment was nitrogen, there were three nitrogen levels (N1：105kg/hm2; Nm:150kg/hm2; Nh:195kg/hm2; calculated by N). Side treatment was potassium, there were five side treatments (K0:0kg/hm2; K4:60kg/hm2; K7:105kg/hm2; K10:150kg/hm2; K7F:105kg/hm2and spraying potassium fertilizer in heading stage and filling stage of rice; calculated by K2O). Combined field experiment and indoor analysis to study the effects of different potassium rates and different methods of potassium application on rice yield and yield composition of rice, dynamic growth of population, nutrient absorption and some related physiological indexs. The purpose of this experiment was to explore the effects of interaction of nitrogen and potassium on regulating growth of rice, nutrient distribution and yield composition, etc. Provide evidence for reasonable applying of potassium fertilizer in high-yield paddy field. The main results were as follows: Both nitrogen and potassium affected the yield of rice significantly, Yield of rice under medium nitrogen level was the highest, yield of high nitrogen level was at the second place and low nitrogen was the lowest. Under three nitrogen levels, potassium fertilizer increased rice yield at different degrees. Spraying potassium fertilizer was benifical to rice yield. Yield of spraying potassium fertilizer treatment was4.2%,4.4%and7.8%higher than no spraying potassium treatment under the same soil potassium application. Yield of potassium fertilizer treatments were higher than no potassium treatment under low nitrogen level, yield of K.7F (applying105kg/hm2K2O in the soil and spraying potassium in heading stage and filling stage) was highest and the next one was K7treatment (applying105kg/hm2in the soil). Spraying potassium fertilizer increased rice yield through increasing the number of effective panicle; Yield of rice was higher at high potassium rate under medium nitrogen level, spraying potassium increased seed setting rate significantly. Under high nitrogen level, spaying potassium treatment had the highest yield, however, yield of each potassium treatment under high nitrogen level was lower than that under medium nitrogen level, high potassium did not decrease the negative effect of excessive nitrogen.Both nitrogen and potassium had significant effects on leaf area index. The interaction of nitrogen and potassium was significant in all growth stages except mature period. Leaf area index of applying potassium treatment was higher than that of no potassium treatment. Spraying potassium could increase leaf area index. Leaf area index of spraying potassium treatment was0.88%,8.66%and9.86%higher than that of no spraying potassium fertilizer treatment respectively. There was positive correlation between yield and leaf area index in mature period of rice. The correlation index was r=0.965**,0.650**and0.535*. Potassium and spraying potassium could increase the activity of POD, positive correlation was observed between yield and POD activity in mature period, the correlation index was r=0.949**,0.950*and0.521*respectively under three nitrogen levels. Dynamic change of SPAD in late growth stage, POD activity and dynamic change of leaf area index were uniform which meant that potassium could delay leaf-senescence in mature period, prolong the time of photosynthesis to make more photosynthetic product amd finally increase the yield of rice.Nitrogen could increase the biggest tiller number. The tiller number under medium and high nitrogen level was5.64%and20.51%lager than that under low nitrogen level respectively. However, the spike rate under medium nitrogen was0.72%higher than that under low nitrogen level, spike rate under high nitrogen level was12.59%lower than that under low nitrogen level which meant that large tiller number did not represent high spike rate. Spraying potassium increased spike rate, spike rate of spraying potassium was19.20%,7.88%and5.46%higher than that of no spraying potassium treatment respectively under three nitrogen levels.Effect of nitrogen and potassium interaction on dry matter accumulation was significant in all growth stages of rice except complete heading stage. Potassium and spraying potassium could increase dry matter of rice. High potassium promoted dry matter accumulation of rice, there was significant difference between potassium treatment and no potassium treatment.; In mature period, amount of dry matter accumulation of spraying potassium treatment was5.26%,3.91%and1.96%higher than that of no spraying potassium treatment.Applying potassium and spraying potassium increased root activity of rice and the nutrient absorption. Interaction of nitrogen and potassium was significant on nitrogen absorption and utilization. Potassium promoted nitrogen uptaking, spraying potassium had significant effects on growth of rice. In mature period, amount of nitrogen absorption of spraying potassium treatment was4.08%,7.62%and4.57%higher than that of no spraying potassium treatment under three nitrogen levels. There was positive correlation between yield and nitrogen accumulation in mature period, the correlation index was r=0.968**,0.936*and0.895*respectively. Potassium promoted the thanslocation of nitrogen from leaves to seeds, however, spraying potassium did not increase the amount of nitrogen translocation and rate of nitrogen translocation significantly. Nitrogen increased content of phosphorus in each organ of rice, spraying potassium increased the amount of phosphorus translocation, amount of phosphorus translocation of spraying potassium was4.03%,20.24%and4.49%higher than that of no spraying potassium treatment respectively under three nitrogen levels. Nitrogen also increased the accumulation of potassium and potassium translocation of rice, amount of potassium accumulation under medium and high nitrogen levels was2.72%and8.39%higher than that under low nitrogen level, amount of potassium translocation was41.85%and20.85%higher than that under low nitrogen level.