Effect Mechanism Of Acidified Soil On Nitrogen Utilization Efficiency Of Different Rice Varieties

Soil acidification directly affects on the roots of rice and enzymes and microbial population in soil, and then affects on growth and yield of rice. To study the influence mechanism of soil acidification on nitrogen utilization efficiency of different rice varieties, based on the results of previous two years, comparative tests in acidified paddy field and simulated acidification pot experiment were conducted with double-cropping late rice varieties with different sensibility to acidification as materials, agronomic traits, yield, the amount of aboveground plant nitrogen accumulation and nitrogen utilization efficiency of different double-cropping late rice varieties were compared between acidified field and normal paddy rice field, photosynthetic characteristics, root morphological and physiological characters and soil biological characteristics of double cropping late rice in acidified soil were studied, and their correlation with nitrogen utilization efficiency was investigated.. The main results were as follows:(1) In acidified soil, growth duration of late rice was prolonged 5-7 day, and the number of tillers, plant height, leaf area index, photosynthetic rate and dry matter accumulation were decreased, and three kinds of acid-sensitive type of double cropping late rice varieties showed the same trend. With the decrement of soil pH,1000-grain weight, effective panicles and yield of acid-sensitive and acid-dull varieties were decreased,the yield of acid-sensitive varieties were decreased 2.02%-24.55%,the yield of acid-dull varieties were decreased 9.18%～10.56%. while the yield of acid-special late rice varieties showed increasing trend.(2) The amount of nitrogen accumulated in different parts of the aerial parts of rice plants was affected by soil pH, nitrogen accumulation in different parts and total plants of three kinds of acid-sensitive type late rice varieties in acidified field showed increasing trend, while rice grain nitrogen production efficiency, nitrogen harvest index and nitrogen physiological efficiency showed the decreasing trend, and mostly showed very significant difference.(3) Simulated pot experiment showed that:Compared with pH6.5 treatment, volume, dry weight and nitrogen content of roots in pH3.5 treatment were significantly decreased, at the same time, root total absorption area, active absorption area and nitrate reductase activity were decreased, while protective enzymes (SOD, POD and CAT) activities were increased.(4) Field and pot test showed that:when the soil pH decreased from 6.5 to 5.2, the soil catalase activity, invertase activity and urease activity were decreased, microbial groups also changed, all of bacteria, actinomycetes, fungi and protozoa were reduced.(5) The correlation analysis showed that positive correlation existed between net photosynthetic rate, stomatal conductance, transpiration rate and nitrogen utilization efficiency, and the negative correlation existed between leaf CO2 concentration, SPAD value and nitrogen utilization efficiency. Negative correlation existed between total absorption area, active absorption area, active absorption area percentage, soluble protein root, SOD, POD and CAT activity and nitrogen utilization efficiency, while positive correlation existed between root activity, root volume, root dry weight, ratio of root to shoot, nitrogen content and nitrogen utilization efficiency. There was a significant negative correlation between nitrate reductase activity and nitrogen utilization efficiency. Correlation between activity of catalase, invertase and urease, quantity of bacteria, actinomycetes, fungi and protozoa and rice grain nitrogen utilization efficiency, nitrogen harvest index and nitrogen physiological efficiency were significant or very significant. So effect of acidified soil on nitrogen utilization efficiency of late rice mainly realized by affecting activity of catalase, invertase and urease, quantity of bacteria, actinomycetes, fungi and protozoa, and nitrate reductase activity, nitrogen content and ratio of root to shoot of roots.