Effect Approach Of Acidified Soil On Yield And Nitrogen Utilization Efficiency Of Rice

Soil acidification is a very serious soil degradation problem in present, and soil acidification in Hunan province is the most serious in China. Field and pot experiments were conductrd in Paddy Field Acidification Monistoring Area of Changsha County, Hunan Province, to study the effects of acidified soil on yield formation and nitrogen utilization efficiency of rice, and the effect approaches of acidified soil on yield and nitrogen utilization efficiency of rice from aspects of photosynthetic characters, roots physiological characters, activity of nitrogen metabolism enzymes and protective enzymes in leaves and roots. The main results were as follows:1. By germination experiments and field experiments, early rice varieties Xiangzaoxian No.45, Luliangyou 611, Luliangyou 211, Lingliangyou 396, T-you 705 and Lingliangyou 104 and late rice varieties Yueyou 6135, Shenyou 9586, Xiangfengyou 103, Zhongyou 288, Fengyuanyou 299, Nongxiang 18, Zhong 9A/R9963 and Zhong 9A/R10402 were classified into acid-sensitive rice varieties. Early rice varieties Xiangzaoxian No.44, De 111A/974, Xinyou 5396, Jinyou 463 and Xin 203 and late rice varieties Yueyou 9113, Shenyou 9588 and ? you 3027 were classified into acid-obtuse rice varieties, and Xiangzaoxian No.42, Lingliangyou 32, Yueyou 6135, Huayou 18, Jinyou 284, ? you 46 belonged to acid-specific rice varieties.2. Acid-sentive varieties were claasified into different nitrogen sensitive types. Among early rice varieties, Lingliangyou 104 and Luliangyou 611 belonged to acid-sensitve type, Xiangzaoxian No.45 and T you 705 belonged to nitrogen-intermedia type, and Lingliangyou 396 and Luliangyou 211 belonged to acid-obtuse type. Among late rice varieties, Xiangfengyou 103 and Nongxiang 18 belonged to acid-sensitve type, Yueyou 6135, Zhong 9A/R9963 and Zhong 9A/R10402 belonged to nitrogen-intermedia type, and Shenyou 9586, Zhongyou 288 and Fengyuanyou 299 belonged to acid-obtuse type.3. Acidified soil induced yield decrease in early rice because of significant decrease of effective panicles and seed setting rate, and its physiological basis were decrease in leaf area, photosynthetic pigment content, net photosynthetic rate, transpiration rate, roots dry weight, roots volume and soluble protein, and increase in intercellular CO2 concentration.4. Under condition of acidified soil, all indexes of nitrogen untilization efficiency of acid-sensitive early rice showed the downtrent, in which N accumulation, N utilization efficiency, N harvest index, N physiological efficiency and N fertilizer efficiency showed significant downtrent for acid-sensitive varieties, only N accumulation, N physiological efficiency and N harvest index showed significant downtrent for acid-intermedia varieties, while almost all of indexes of nitrogen untilization efficiency were decreased unclearly for acid-obtuse varieties. Looken from photosynthetic characters, the derease in N accumulation was induced by decrease of stomatal conductance, transpiration rate, net photosynthetic rate and increase of intercellular CO2 concentration, which were induced by decrease of chlorophyll content. Decease of N utilization efficiency, N harvest index, N physiological efficiency mainly induced by decrease of net photosynthetic rate, stomatal conductance and transpiration rate and increase of intercellular CO2 concentration caused by decrease of leaf area, photosynthetic pigment content and soluble protein content in leaf. Looken from roots physiology, decrease of roots volume and dry weight was the main reasons for decrease of N physiological efficiency, and the decrease of N utilization efficiency mainly related to decrease of total absorption area, active absorption area and volume of roots.5. N accumulation, N utilization efficiency, N fertilizer efficiency and N physiological efficiency of acid-sensitive late rice varieties showed the downtrent in acidified paddy field, in which N physiological efficiency of all varieties showed very significant downtrent, and the significance of decrease of the former three indexes related to nitrogen-sensitive type, that was to say, nitrogen-sensitive varieties showed very significant downtrent, nitrogen-intermedia varieties showed significant downtrent and acid-obtuse varieties showed unclear change. Correlation analysis between roots physiological characters and indexes of nitrogen utilization efficiency showed that effect of acidified soil on nitrogen utilization efficiency of late rice was realized by affecting on roots POD activity and roots vigor.6. Comprehensive considering pot experiments of early and late rice, soil pH evidently affected yield and its components of rice. Lower soil pH resulted in relatively slow rice tillering rate at early tillering stage, the relatively late peak tillering stage, the highest tiller number and more effective panicles per hill, and lower seed setting rate. Correlation analysis showed that the effect of soil pH on rice yield was mainly realized by affecting on roots vigor, chlorophyll content and CAT activity in leaves.7. Pot experiments of early and late rice showed that effects of soil pH on rice N accumulation, NUE and others N utilization efficiency indexes were significant, while there existed differences between early rice and late rice, among treatments and indexes. Correlation analysis showed that effects of soil pH on N accumulation and NUE of rice were realized by affecting on roots vigor, chlorophyll content, POD and CAT activity in leaves and soluble protein in roots, and the effects of soil pH on N utilization efficiency, N harvest index and N physiological efficiency of rice were realized by affecting on chlorophyll content, roots vigor, activities of SOD, POD, CAT and NR in leaves.