(22(2):77-97)THE CHARACTERISTICS AND GENESIS OF PADDY SOILS IN NORTHERN PART OF TAIWAN

研究之範圍包括本省北部地區：臺北、宜蘭、桃園、新竹與苗栗五縣，選其重要類型水稻田土壤進行研究，目的在加深對該區水田土壤本身特徵之認識與瞭解，以為管理培肥及土壤分類之改進作參考。採集代表剖面12個，分析其理化性十三項目，結果以圖17種，表十個分別討論其特質及水稻土之生成，玆摘要如下： 1. 十二土壤剖面中有洗入及洗出層之生成者凡六土型，堪稱水稻土（Aquorizems)，餘六土型仍列入原土類，而以稻田形容其亞類；分類結果有三土類、六亞類、十一土系，十二土型，詳見表二；各剖面形態見表三。 2. 稻田土壤代表剖面各層次中細質地占大多數，中質地次之，粗質地垠少，見表四；水稻土六剖面中大部屬中質地，為其特點。 3. 各類型土壤之容積重在剖面深度之變化不一，見圖1至圖3，58分析樣本中平均容積重為1.55g/cc，最低未少於1.2g/cc，最高則超出1.8g/cc，見表七。 4. 表土孔度較高，平均46%，亞表土與底土相差至微，全部樣品中孔度最低為32%，圾高為55%，平均約為42%，見表八。 5. 水稻土六剖面之游離鐵及游離錳曲線，均顯示有由表土下移並積聚於亞表土，見圖4及圖5。 6. 各類型土壤之有效矽，在各該剖面層次之變化多趨向一致，見圖6a、7a、8a、及9a。至於各類型土壤之CEC，在該剖面層次之鑾化則趨向各異，見圖6b、7b、8b、及9b。 7. 土壤反應在各類型剖面中變化之型式，則水稻土均屬D型，見圖10a、10b，稻田灰粘土則四結坋壤土接近C型，見圖11a，城仔粘壤與下大掘坋粘土接近B型，見圖11a，稻田黃棕壤二土型亦類似B型，見圖11b。 8. 各類型土壤之平均C/N比率相差至微，最高與最低則超出三倍，總平均為6.8，見表九。剖面各層次顯示表土之比率平均較高，隨土層深度而愈減低，見表十。 9. 灰色水稻土與稻田黃棕壤之有機質，在其剖面中之變化曲線趨向尚一致，即自耕犁層急劇降低，至亞表土以下則緩慢減低，見圖12及圖14。灰棕色水稻土與稻田灰粘土諸代表曲線各異，見圖13及圖15。 10. X光繞射線分析見圖16，顯示四結坋壤土之五層次均有綠泥石與伊來石之存在，示差熱之分析結果見圖17，顯示柑園坋粘壤土有伊來石之存在，觀音坋粘土有少量高嶺石之存在。 11. 各類土壤受種植水稻之影響如下：a. 質地中等之土壤對水稻土之育成較易。b. 磚紅化土質地多偏於粕重，雖長期用為水稻田，除耕摯層外，仍多保存其原有特性。c. 灰粘土原係受高的地下水位影響所育成，水稻耕作對該土之影響不大。 This study includes the soils of paddy field of Taipei, I-lan, Taoyuan, Shinchu and Miaoli, the northern part of this province. The objective is to study the improvement of soil management, soil fertilization and soil classification in order to emphasize the reconi-zation and understanding of the soil proper characteristics of the paddy soils in Taiwan. Twelve soil profiles of representative soils according to their important patterns were sampled, and 13 items of the physico-chemical properties were analyzed. All the results are shown on appendix 1, 2 and 3. All the characters and the genesis of the 12 representative soils profiles are discussed in relation with 10 tables and 17 figures. It may be summaries as follow: 1. Six soil types may be classified as aquorizems by the development of their eluvial horizons and illuvial horizons. The other 6 soil types still belong to original soil groups and can be modified with “paddy” as sub-group. There are 3 great groups, 6 sub-groups, 11 soil series and 12 soil types based on the result of classification. It is shown on table 2, and the soil profile description is shown on table 3. 2. With all the soil sample studied fine texture occupies the largest proportion, moderate textured comes to the next and coarse textured soils the least, it is shown on table 4. It is rather special that most of the aquorizems are moderate in texture. 3. The changing pattern of soil bulk density with the soil depth in a given profile varies with different types of soil. It is shown on Fig. 1 to Fig. 3. The average bulk density of the 58 samples is l.55g/c.c., the lower limit is not less than l.2g/c.c. and the highest is over l.8g/c.c., it is shown on table 7. 4. The pore space of the surface soils is high showing on the 46% on the average the difference between sub-surface and the sub-soils is small. The lowest of the whole samples is 32%, the highest is 55% and the average is 42%, it is shown on table 8. 5. The distribution patterns of the free iron and free manganes of the six profils of aquo rizems show the accumulation of these elements in the sub-surface soil by leaching from surface soil as shown in Fig. 4 & 5. 6. The available silica content shows only slight changes as it goes down from surface to sub-soils as shown in Fig. 6a, 7a, 8a and 9a. On the contary, C.E.C. shows a great variation under the same conditions, it is shown in Fig. 6b, 7b, 8b, and 9b. 7. From the pH patterns of the soil profiles, it is concluded that the aquorizems belong to D types as shown in Fig.l0a and l0b. The Szu-chieh silty loam approaches C types as Fig. ha. The chengtze clay loam and Hsiatachu silty clay and the two soil types of the paddy yellowish brown latosols approaches B types as Fig. 11a and Fig. 11b. 8. The variation of the avcrage C/N ratio among the different soil types are very small, but variation of the sampling within a soil type is high. The grand average is 6.8, it is shown on table 9. The average ratio of surface soils is high and decreases with the depth of the profile, it is shown on table 10. 9. The organic matter content shows a rather uniform distrbution over the entire soil profile in the gray aquorizems and paddy yellowish brown latosols. It is found that the value decrease sudenly from plow lazer, but slowly after reaching sub-surface soil, it is shown in Fig. 12 and Fig. 14. The curves of the gray aqorizems and paddy gley soils are variant as Fig. 13 and Fig.15. 10. X-ray diffraction pattern is shown in Fig. 16, it shows that there is some chloride and illite in all of the 5 layers of the Szu-chieh silty loam. The results of D.T.A. is shown in Fig. 17, it shows that some illite is present in Kan-yuna silty clay loam and small amount of kaolinite is present in Kan-jin silty clay. 11. The influence of various great soil groups by rice planting is as follovng a) Aquoriz-ems was easier to be developed by the soils which are moderate in texture. b) The texture of latosols is mostly heavy, althogh it was used as paddy for a long time, but the original characters were still conserved except the plow layer. c) The gley soils were original developed by the effect of high ground water table, so the influeuce of these soils by rice planting is not great