Question

1. Summarize"Soils of the Tropics and the World Food Crisis" the article in a paragraph, making sure to hit all of the key points.

2. Consider the issues noted in the article regarding feeding the world. How might soil taxonomy be implemented to solve this large undertaking?

3. Explain why simply indicating that tropical soils are not sufficient for crop growth is considered an over-generalization. What usually comes to mind when you think about the tropics?

4. What is base saturation and why is it important for crop growth? How does it differ in soils from different regions?

5. Peer Responses: Through peer responses, discuss the feasibility amongst yourselves of the strategies discussed in the reading regarding improving soils for cultivation in the tropics. Do you think they will work or not? Are the options presented even affordable to rural poor in the tropics? Explain why or why not. I would like for everyone to come to a consensus in this post.

Answer 1

• 1. Tropical alluvial soils are azonal, usually defined as young sods of recent and subrecent sedimentary deposits, without horizons or with only weak ones.
• The concepts Alluvium and Alluvial soils have various meanings. In geology Alluvium is a deposit of the Holocene Period. In sedimentology Alluvium often refers to sediments deposited in recent flooding, whereas in geography Alluvial plain means a flood-plain or river valley.

O. De Schutter, UN Special Rapporteur on the Right to Food, sees the emergence of a new world food order as a response to the 2007-08 food crisis (HRC 2008b, 32-35). There is no denying that battling hunger and ploughing funds back into agriculture are topics now receiving attention internationally; and there is no denying that international organisations and States have made efforts to increase coordination. The creation of the High-Level Task Force on the Global Food Security Crisis for bringing together the heads of all UN agencies is without parallel, as are the reform of the CFS and the creation of the Global Partnership for Agriculture and Food Security.

2. Classification of Histosols aims to stimulate use of the system in developing countries. It is by no means complete, however, so there is a need to expand upon it. The lower categories need particular attention for use in tropical countries. Detailed information on chemical characteristics, on the nature of the mineral part of the organic materials, for example texture, must be used for a further subdivision. Lucas (1982) mentions the use of parameters such as texture of mineral subsoil, presence of iron, kind of limnic material, depth of peat, soil reaction (pH) and soil temperature class for a separation at family level. In the USA, however, they use properties such as pH, temperature class, depth and the mineral soil texture within and/or below the organic soil layer at series level. It should be emphasized that, by definition, the Histosols are allowed to contain a considerable amount of mineral matter and for practical management purposes it is important to realize the difference between a soil with no mineral material and a soil with say 40 percent mineral matter. At a high level of classification such differences are not immediately obvious. Loss on ignition is therefore regarded as a key parameter which is easily analysed and which should be used as an important diagnostic feature in any system set up locally. Knowledge of both the depth and nature of peat beyond the 1.6 m control section and of the underlying material is essential to enable predictions of the behaviour of peat soils upon drainage and to estimate the lifespan of this wasting resource. Local systems should be geared to management requirements, including water control, so they should modify and supplement Soil Taxonomy.

3. In many regions the productivity of Alluvial soils is low, partly because of low natural fertility or high acidity, but more through floods and inunda-tion, because most low-lying Alluvial soils are not protected by dikes and there are no pumping stations that can drain the land. Very often the period in which Alluvial soils can be cultivated is short and only crops with a short growing season can be grown. In some regions there is salinization or alkali-zation, in others a dense vegetation or there are no roads. In many coastal
areas soils are unripened clay soils, that become acid sulphate soils on reclamation. The special crop of Alluvial soils is rice, but sugar-cane, bananas and on better drained sites cocoa, coffee and citrus are grown too. Although
tropical Alluvial soils are not considered to be as good as those in temperate regions, they still have great potential. However it is extremely difficult to reclaim such soils, not technically, but because of economics and sociology.

4. Positively charged soil nutrients are called cations. Cations spend time on the soil exchange sites,
clay and organic matter, or in the soil solution. The ratio
between cations on the exchange sites and cations in soil
solution is directly affected by the base saturation percentage
of each cation. This is why we need to take base saturation
into account when calculating fertilizer and amendment
applications. The amount of fertilizer and amendments
required to correct soil problems can vary greatly depending
upon the soil’s base saturation.

The CEC of soil organic matter and some clay minerals varies with pH. Generally, the CEC is lowest at soil pHs of 3.5 to 4.0 and increases as the pH is increased by liming an acid soil, as shown in Figure 2. Because CEC may vary considerably with soil pH, it is a common practice to measure a soil's CEC at a pH of 7.0. Also note that some positive charges may occur on specific soil mineral surfaces at low pH. These positive charges retain anions (negatively charged ions) such as chloride (Cl-) and sulfate (SO42-).

a. Coastal Plain (includes Atlantic Flatwoods and Sand Hills): Soils have sandy surfaces and a CEC of 6 meq/100 g or less. Soils in their native state can be acid and infertile. Soils will vary in clay content, drainage characteristics and color. Soils will vary in productivity, ease of handling and adaptation to row crop production. Typical soil types are Norfolk, Lakeland, Lynchburg and Tifton.

b. Piedmont soils: Soils are predominately upland, well-drained red soils with a CEC of 6 to 12 meq/100 g. Soils in their native state are acid and low in phosphorus but higher in potassium than the Coastal Plain soils. Major soil series are Cecil, Madison and Davison.

c. Mountain and Limestone Valley soils: Soils may have a gray, sandy surface underlain with a heavy red sandy clay or clay texture soil. The alluvial terraces and river bottoms are gray to light brown in color with yellow to dark red sandy clay loam subsoil. Soils are acid and low in fertility. The average CEC value of these soils is 9 meq/100 g. The major soil types are Porters, Hayesville, Talladega, Fannin, Congaree, Clarkesville, Fullerton, Dewey and Decatur.

d. Soils from landscapes and golf greens: These soils are frequently maintained differently than crop soils and are usually artificially constituted and maintained. Many are erratic in fertility and cannot be easily placed in one of the three categories given above.