@Shubham Lamba

@Shubham Lamba

Dear Shubham - You are right, though I am yet to get the results of SOC & N from the soil test laboratory for the sampled soils collected from the each soil layers of 20 cm within the soil profile of 1m depth. In the mean time, I read out several literatures regarding vertical distribution of soil organic carbon and nitrogen, and almost all the literatures show the uniformly decreasing trend of SOC & N content with the increment of depth, and bulk density increases with the depth within the soil profile of 1m depth and all these papers are related to the forest soils, still I am in the same boat of thoughts that you have elaborated about the vertical distribution of the soil parameters.

Dear Elaheh - Do you possess the same thoughts as observed by Shubham Lamba, or something different as per topographical features of your areas

Dear Gautam,

In the case of this discussion, I am totally in agreement with the statements and thoughts of Shubham. He explained the issue as well. I am specifically a soil ecologist and zoologist and I am also concerned about issues related to physical and chemical properties of soil. Thank you for your precision. Good luck.

Best, Elaheh

Elaheh - I have found several data during my course of study related to the forest soils which do not show similaritiness with those of the conventional data found in the literature, and those data are almost everytime close to the data of previously published literature, sometimes it is embarrassing.

On observing the vertical distributions of soil organic carbon (SOC) & available nitrogen (N) in soil profile, it will definitely decrease with increasing depth. The higher bulk density in the lower layers of soil is due to the less SOC. The volume of soil is more important for bulk density of the soil which is directly and largely controlled by the SOC than soil structure and texture of the soil. It is very common in all the soils (generally the soil may have 50 percent of the pore space). The forest soil also follow the same trend. But the rate of decrease of SOC and available N with depth may vary and depends on the impact of soil forming processes taking place in a particular soil.

Jothimoni Subbiah - Definitely the SOC content & N concentration are decreased with the increment of the depth within the soil profile, and simultaneously, the bulk density has increasing trend, it is conventional, but in the forest soils, particularly where the soil is not compressed by the outside agents like vehicles or tractors, or soils are not affected with the tillage like mechanical manipulation that happens in the agricultural lands, variations in the vertical distributions of SOC & N are expected due to the rate of leaching i.e. rate of draining away of soil nutrients and organic carbon from the surface soils and particularly for the vegetation characters of different forest types occurred in the different topographical areas that supply litterfall for the microbial biomass decomposition. But the literatures show no diversity/variations of content in their occurrences within the soil profile up to 1m depth, though I have not read out yet all references regarding vertical distribution of these soil parameters.

Soil organic matter (SOM) has three main fractions, fresh undecomposed residues, decomposing and partially decomposed materials, and a highly decomposed and stable product humus (it is not completely decomposed organic matter; complete decomposition of organic matter produces carbon dioxide, water, and other inorganics). Plant litters including dead leaves, stems, barks, flowers, fruits, and logs are the major sources of forest SOM. Soil animals, microorganisms, and roots also contribute to the SOM. The threshold value for organic matter in agricultural soil is 2 % by weight, beyond which soil quality does not remain sustainable, but no threshold level for forest soils has so far been established. Forest mineral soils have generally 1–5 % organic matter by weight.

Forest soils usually have higher organic matter than agricultural soils. There are two types of organic matter in soil, active or labile and passive or stable. Humus is the stable fraction of SOM. Forest ecologists identify three types of humus: mull humus, mor humus, and moder humus depending on the degree of decomposition and integration with mineral matter, acidity, and base contents. This categorization is more pronounced in temperate and boreal forest soils. A deep O horizon also develops in these types of forests. So no variation in SOC and N in the forest soil may be due to the presence of thick O horizon than other horizon with in 1 m depth as observed by Gautam Kumar Das.

The list of literature attached may be useful to enrich the knowledge on distribution of SOC and N in forest soil.

Deep into the forest soils, it is made of layers, or horizon, and that is an organic (O) horizon composed of mostly organic matter such as decomposing leaves and that layer is almost equivalent to the eluviated (E) layer comprising leached of clay, minerals, and organic matter, leaving a concentration of sand and silt particles of quartz or other resistant materials that is too found in the forest soils. Leaching is a primary process for such horizon for passing of soil nutrients and soil organic carbon with the increment of depth within the soil profile. The content of organic carbon and nitrogen concentration might depend upon the rates of leaching of soil organic matter along the soil profile, but not with the leached clay as the value of SOC & N cannot be obtained from the soil sample analysis, and they are not available for absorption by the forest vegetation.