There seems to be a standard range of the level of organic matter in the soil in order to refer to a soil as fertile. For instance, according to Metson (1961) as adapted from Booker Tropical Soil Manual (ed. Landon); the level of organic matter of 17.2-34.4 in soil was considered high. Is this classification regional, continental or does it depend on ecological zone?
Yes of course if the soils were located in or near the forests the OM % will be much high, resulting in the rich fertility of soils.
note: this classification seems to be regional. As in Pakistan soils having 1 % OM value are considered to be fair. While it goes to 17 in the hilly and mountainous regions always covered with plants
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A general answer is YES, of course. It is a regional issue. But you need to specify an ecological zone first. This is too broad to answer you specifically.
@Antonin, Thank you. My consideration is humid ecological zone of Africa compared with other region of the world.
Aloha Clement. I would say the amount of organic material to be considered "fertile" soil depends on many things. Ecological zone will have an effect, but much more the effect will depend on the soil that the organic matter is added to. Soils with high natural fertility, reasonable pH, and a 'good' mix of sand, silt, and clays may have high nutrient concentration, retention, and availability for plants so that the concentration of organic matter may not matter much.
Organic matter in soils in general does several things. One it that it enhances moisture storage, which typically is a good thing for fertility. Organic matter will also tend to come with some nutrients, and increase total nutrients in the soil, also good for fertility. But organic matter can also have negative effects on fertility as well. Organic matter will typically decrease the pH through organic acids, which will decrease the zero point of charge and therefore in some cases lower the retention of important anion nutrients, the most important being nitrate and phosphate. Organic matter is already very acidic soils will therefore not do much for fertility, nor will it persist long. Organic matter will virtually always increase the retention of free cations, such as exchangeable calcium, sodium, magnesium, etc.
One last aspect of organic matter I would consider is that it will affect the microbial community very significantly, which will very much affect the cycling of nutrients. This can go both ways, again depending on the soil. For example the increase of organic matter will allow microbial communities to increase ad therefore releasing nutrients from more stable forms. This may increase nutrient availability to plants, but it also increases the potential for leeching form the system. So I think there is a balance there.
In short I would say one cannot generalize about high organic matter content making a fertile soil, and it will depend on the ecosystem to a point, but much more depend on the stage of soil pedogenesis.
Dear Clement Ogunkunle, definitely depends on the ecological zone y course that soil fertility is closely linked to the content of organic matter, the reason lies in several aspects:
1. - The higher the organic matter content in soil greater nutrient recycling.
2. - A higher percentage of organic matter in the soil it will increase your ability to retain nutrients.
3. - A higher content of organic matter in the soil the greater the proliferation of macro and micro flora and fauna.
4. - In soils with pH tending to alkalinity, organic matter bring us closer to a neutral pH.
5. - And another very important from the point of view of agriculture, is the greater the amount of organic matter in agricultural soil, it will improve its structure, moisture retention, and manageability for easier farming way different.
Thank you Lincoln and Lopez for those contributions!!!!!!!!!!! Viola!!!!!!
I would disagree a bit with Celso in point 1 :)
In forest soils, especially under conifers (high mountains, boreal areas), despite a huge amount of OM (even organic soils, peat), recycling is highly limited due to climate, so again, zone is important to define. I know, this is not a case of tropical areas, Clement.
There is a strong relation between Climate zones and OM .
The amount and quality of humic substances dependes on Period of Biological Activity.
And this doubtless affecting on fertility.
In Russia this studies were started by Vasily Dokuchaev and this time it is resalted on detailed maps of humus status of soils of RF
Yes, Mikhail. This is a good point.
Clement, please see that Dokuchaev concept of soil zonation and related zonal concept used in classification of forests in the North Hemisphere (especially in British Columbia). It has much to do with soils and OM! You may apply this concept to Africa, I think and it is really a gallege!
Thanks Antonin, climatic condition has alot to do with soil fertility as you have rightly said. Cold condition may prevent organic matter present to be phytoavailable due to low decomposition or reduced microbial activities. I really appreciate your contribution.
Thanks alot
Clement, sorry for the typo before. In the last sentence I wanted to say: I think it is a really challenge!
Antonin You are quite right, we should not generalize, it's definitely the soil temperature that defines the growth of microbes degrading the organic matter and all processes resulting from this, do not put attention on the looks "temperature". My opinion only applies in areas not so cold or warm.
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