Weathering is the alteration by chemical, mechanical, and biological processes of rocks and minerals at or near the Earth’s surface, in response to environmental conditions.
Highly weathered soils (or strongly weathered soils) are soils that have undergone prolonged and intense weathering under the net leaching environment of the humid tropics. They are commonly found on stable and old geomorphic surfaces underlain by easily weatherable rocks such as ultrabasic and basic rocks as well as by pre-weathered sediments (Beinroth, 1982). These soils are clayey, deep, reddish, acidic, and have low nutrient status. According to Jackson et al. (1948), highly weathered soils are characterized by weathering stages of 10 to 12 wherein the clay fraction is dominated by 1:1 phyllosilicates (kaolinite & halloysite), aluminum oxide (gibbsite), and iron oxides (goethite and hematite). This mineralogical characteristic is also predicted by the “residua hypothesis” of Chesworth (1973) which states that soil composition will with time move towards the residua system composed of SiO2, Al2O3, Fe2O3, and H2O. In the USDA Soil Taxonomy, the highly weathered soils belong to the Ultisols and Oxisols orders. In the World Reference Base, these soils belong to the reference soil groups Alisols, Acrisols, and Ferralsols. These soils possess nutritional problems for crop growth and thus are a problem for agriculture.
(Beinroth, F.H. 1982.Geoderma 27(1982)-1-73; Chesworth, W. 1973. J. Soil Science 24: 69-81; Jackson, M.L. et al. 1948. J. Physical and Colloidal Chemistry 52: 1237-1260).
Below are photos of the important highly weathered soils from Leyte, Negros and Samar islands in the Visayas.
 |
| This is an Oxisol that formed from ultrabasic rock in Salcedo, Eastern Samar |
 |
| The widespread red soil (Ultisol) in the volcanic area of Central Negros |
 |
| An Ultisol on pre-weathered sediments from basalt in Silago, Southern Leyte |
 |
| An Ultisol formed on pre-weathered sediments from basalt in Biliran, Leyte |
 |
The widespread soil from basalt on the lower slopes of Mt. Pangasugan, Baybay, Leyte
|
3 comments:
Prof. Vic maayong hapon! Buddy Vargas here of Sagrex Corporation in Luzon.
Am doing a little study on the availability of citric acid in soil to improve solubility of phosphates.
One study says that on highly weathered soils, phosphate effectiveness is greatly compromised. My question is that, in the Phils, areas / lands devoted to corn and rice production, can it be classified under "weathered soils"?
Salamat kaayo for any feedback!
Hello Buddy,
Good afternoon. Thank you for visiting my blog and for leaving a note. Yes, it is true that P availability is a problem in acidic soils such as those "highly weathered soils". This is because P is fixed by aluminum and iron which are highly soluble under acidic conditions. Most lands devoted to rice and corn are alluvial or lowland soils which are mostly young soils (meaning they are not highly weathered soils). So in most of these soils, except if they are really acidic (pH below 5), P is not much a problem. A good indicator to know if the soils are highly weathered soils is to observe their color and texture. Highly weathered soils are reddish and clayey such as those common in Claveria and Bukidnon. I hope I answered your question. If you have more questions please free to email me at: vbasio@vsu.edu.ph
Vic Asio
Hello Sir Vic, I'm Christopher Capito, I am searching for some information about ultisols especially in Bukidnon for our learning activity in Hort 141. I find your blog very comprehensive. God bless sir!
Post a Comment