|Title:||臺灣主要土壤含氮狀況與其供應情形||Other Titles:||The Nitrogen Status and Nitrogen Supplying Power of Taiwan Soils||Authors:||林家棻
|Issue Date:||3-Sep-1973||Publisher:||農業試驗所||Journal Volume:||22||Journal Issue:||3||Start page/Pages:||186-203||Source:||農業研究||Abstract:||
1. 本省主要農田土壤，經熱鹽酸處理後，所得有機態氮之分佈（以全氮作100計算）如下：(a)非水解性氮(non-hydrolyzable-N)為24.4%，(b)水解性氮(Total hydrolyzable-N)為75.6%，(3)胺基酸態氮為35.7%，銨態氮包括Amid態及非蛋白質態氮為25%，Hexosamine-N為4.8%，其他未知態氮為10.5%。此等有機態氮之分佈與土類間之關係不明顯，但與土壤若干性質則有顯明關係，如粘土含量、有機物、全氮及陽離交換能量等，其中尤以有機物及全氮與土壤水解性總氮量及胺基酸態氮之相關係數均在0.9以上。
3. 潛水保溫培養所產生礦物化氮的累積量與培養時間（星期）的平方根成直線型的關係。由此顯示在潛水之下，土壤中銨態氮的釋放可以log(N0-Nt)=log N0-k/2.303(k)公式表示之，式中N0=氮礦物化能量，Nt=培養期間生成礦物化氮的累積量ppm，t=培養時間，k=常數，視個別土壤而定。由此公式所求得的氮礦物化能量（N mineralization potential）與水稻氮吸收量有顯著的關係。
Nitrogen in the soil is almost always in the organic matter and as such is not directly utilizable by plants. Before, it can be taken up by a crop, the nitrogen must released through decomposition of the organic matter and transformed to the nitrate and ammonium forms of nitrogen. Since decomposition and transformation are biological proceses, they are affected by weather, soil texture, soil management, previous crop and other variables. The dependence of nitrogen availability on microbial activity makes testing for available nitrogen a more difficult problem than testing for available phosphorus and potassium. However, the nitrogen fertility of soil plays a crucial role in lowland rice production. It is necessary to know the behavior of native nitrogen during the growing season in order to control the N uptake by rice plants at each stage for getting adequate grain yield.
Twenty soil samples from plow layer scattered widely over the Island were taken to study the N distribution after acid hydrolysis, the liberation of mineralyzable N, the biological and chemical methods for measuring soil N availability. All the tested values were calibrated with the N uptake of rice and the percentage yield of rice in order to understand the N status and N supplying power of Taiwan soils. The results may be summarized as follows:
1. The average distribution of different forms of N calculated as percentage of total N was as follows Non-hydrolyzable N (24.4%), total hydrolyzable N (75.6%), amino acid N (35.7%), hydrolyzable ammonium N (25%), hexosamine N (4.8%), and unidentified N (10.5%), The relation between N distribution and soil groups was obscure. However, significant correlations between some soil properties (organic matter, total N, clay content, cation exchange capacity)and various forms of N after hydrolysis were found. Among them, the correlation coefficients of soil organic matter as well as total nitrogen to the total hydrolyzable N and amino acid N were extremly significant (over 0.9).
2. Nitrogen values obtained after intermittently two-week waterlogged incubation were closely related to the contents of total hydrolyzable N, amino acid N, and unidentified N, So was the N-uptake of rice plant It, thus, indicated that mineralizable N produced under two-week period of waterlogged incubation will reveal the nitrogen supplying power of paddy soils.
3. Cumulative net N mineralization was linearly related the square root of time, t , throughout the 12 weeks of intermittent incubation with most soils. Because of the generally consistant results, the data were employed in calculating the N mineralization potenial, N0 of each soil, based on the hypothesis that rate of N mineralization was proportional to the quantity of N comprising the mineralizable substrate. Values of N0 ranged from 90 to 340 ppm of air-dry soil, and they were closely related to the N-uptake of rice plant.
4. Rates of N mineralization (ppm N/week ) declined gradually with increasing duration of incubation with most soils. However, the relative low rate of mineralization during 0-2 weeks was found among them, it may reflect lag in microbial activity and/or assimilation of N by organisms owing to decomposition of small amounts of low-N plant material. The N mineralization rates of some soils were essentially constant or even gradually increase for all cumulative periods from 0-12 weeks. N-uptake of rice was closely related to N mineralization rate obtained at each period of intermittently two-week incubation.
5. Among the biological and chemical assays, N values obtained from the 1-week period of waterlogged incuation at 40°C was comparable to those from two-week period of incubation. and N value from micro-diffusion method in which ammonia released on treating soil with normal sodium hydroxide agreed moderately well to those from two-week period of incubation.
6. Highly significant correlation existed between N-uptake of rice from no N pot and combined N values obtained by 1-week period of waterlogged incubation and inital NH4-N. So was the percentage yield of rice grain. Among chemical assays, only micro-diffusion method gave N values fairly related to N-uptake of rice from no N plot as well as to the percentage yield of rice. However, the coefficients of determination f or these relationships obtained by chemical assays were appreciably lower than those by waterlogged incubation.
In conclusion, ammonia production after 1-week period of waterlogged incubation at 40°C agrees extremely well with the N-uptake of rice or the N supplyng power of the souls under certain conditon. As this method is rapid and precise and is readily applicable to both air-dried and field moist soil, it can be employed, to study the liberation .of native nitrogen under various field conditions in order to understand the nitrogen fertility of paddy soils.
|Appears in Collections:||1.台灣農業研究(1950～迄今)|
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