臺灣主要土壤含氮狀況與其供應情形

The Nitrogen Status and Nitrogen Supplying Power of Taiwan Soils

林家棻(C. F. Lin) ； 張愛華(A. H. Chang) ； 曾肇清(C. C. Tseng)

《中華農業研究》 22卷3期 (1973/09) Pp. 186-203

https://doi.org/10.29951/JARC.197309.0003

摘要

從全省各地農田選取代表性表土樣本20種，以探討本省主要土壤中有機態氮之分佈狀況，潛水保溫培養下礦物化氮之釋放情形及氮有效指數之測定法，所得結果并以溫室盆栽水稻校正之。藉以暸解本省土壤含氮狀況與供應情形。茲將所得結果摘要如下：
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)爲24.4%，(b)水解性氮(Total hydrolysable-N)爲75.6%, (3)膠基酸態氮爲35,7%，銨態氮包括Amid態及非蛋白質態氮爲25%，Hexosamine-N爲4.8%，其他未知態氮爲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。
2．潛水保溫培養兩星期所產生的礦物化氮與土壤中未知態氮，水解性總氮量及有胺基酸態氮均有密切的關係，水稻氮吸收量亦與上述三形態氮間有顯著的關係。由此顯示，在一定環境之下，保溫培養法所得礦物化氮確可反映土壤氮素供應情形。
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(N(下標 o)-N(下標 t)=log N(下標 o)-k/2.303(k)公式表示之，式中N(下標 o)=氮礦物化能量，N(下標 t)=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。由此公式所求得的氦礦物化能量(N mineralization potential)與水稻氦吸收量有顯著的關係。
4．各法所得氮有效指數與潛水保溫培養兩星期所產生礦物化氮之相關係數中，以潛水保溫培養一星期者最高，其次爲微量擴散法，其他方法之相關係數均未達顯著平準。由此顯示潛水保溫培養時間可縮短爲一星期。
5.各法所得氮有效指數與稻谷收量百分率及水稻氮吸收量之相關係數中，仍以一星期潛水保溫培養法及同法再加土壤中原有NH4-N者最高，且達極顯著平準，其次則爲微量擴散法，所得相關係數雖然亦達到顯著平準，但遠低於潛水保溫培養法。
綜上而言，在一定環境之下，潛水保溫培養法所得氮有效指數確可反映土壤氮素的供應情形，此法簡易精確，可供今後加強研究在各種環境下，土壤中礦物化氮之釋放情形，藉以增進稻田氮素肥力之暸解。

並列摘要

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(1/2), 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 340ppm of air-dry soil, and they were closely related to the N-uptake of rice plant.
4. Rates of N mineralization (ppm N/week (1/2)) 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℃ 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 for 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℃ agrees extremely well with the N-uptake of rice or the N supplyng power of the soills 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.