Soil Report on the Nibenay Valley

So after talking to a few people in this thread about soils, I decided to write this up. Originally I was going to talk about the soils of all the different provinces, but I wouldn’t be able to stop myself from writing a 20 page paper, and have written far too any papers in the last couple weeks. So instead I decided to pick an interesting area to break down. If this is enjoyed I can pick another area and do that as well.

Delvin Gaerston

Agricultural Advisor to the Elder Council

Report on the Soils of the Nibenay Valley

This report is being compiled on the orders of the Elder Council. The Nibenay Valley has long been the bread basket of the Empire and is one of the most important regions of Tamriel. The aim of this report is to inform the Council on the morphology and productivity of the soils around the Niben and Lake Rumare.

The Nibenay Valley is prime farmland. The lands directly bordering the river are primarily formed of recent alluvium overlying base residuum or, in areas closer to the eastern highlands, recent alluvium overlying colluvium. Residuum being non-transported, weathered bedrock, colluvium being material moved by gravity over long periods of time. Alluvium is material transported and deposited by water. It tends to be loose and unconsolidated due to the short amount of time it has been in place. This allows for quick percolation rates and high hydraulic conductivity. Redoximorphic features (features developed in soil due to the presence of long periods of water exposure, i.e. the water table) are likely to be found in the upper horizons of the soil, possibly in the upper 50 cm. These regions are all subject to flooding due to their proximity to the river. Due to the high water table and risk of flooding, the lands directly bordering the river are not suitable for roads or any buildings with any basements or underground structure. They are, however, very suitable for agriculture. Alluvial soils tend to have a high amount of organic content due to their proximity to a water source. Organic content provides many of the nutrients crops require and promotes agglomeration of clay particles, improving hydraulic conductivity.

The regions just beyond the alluvial floodplains have formed stream terraces. As a river (or any other waterway) gradually erodes the land beneath it, it gradually moves lower and lower. Therefore the lands that once were floodplains are now elevated lands above the current floodplain. While not still regularly flooded, these landscapes were formed with very similar processes to the floodplain soils. These regions are likely an even more agriculture friendly. Not only do they have the alluvial organic matter, but do to the flat, plain-like landscape (especially on the western side of the Niben) also allow for a development of a loess top-layer. Loess is wind transported material that is loosely consolidated and usually contains high organic material. This means even more fertile material in the upper layers of the soil. The water table will almost certainly be lower than in the floodplains, so short depth, manual wells would be a smart investment. These would be relatively cheap to construct and would provide a safety net for the Empire’s cash crop production in the case of drought. These regions are also very suitable for the construction of roads and infrastructure. There is a far less risk of flooding, the water table will should not be a problem due to a lack of limiting layers, and the soil particles are mostly coarse, sandy, or skeletal (containing significant large rock fragments). The particle size is important because smaller sized particles, like silt, have a risk of contraction and expansion due to freeze-thaw forces.

The upper reaches of the Nibenay Valley and the lands around Lake Rumare do not have the alluvial soils seen further down river. Instead they are composed mostly of loess over residuum with the possibility of colluvium on the northern part of the lake due to the hilly regions leading to the Jerall Mountains. There is less stratification, or change in parent material, than seen in the alluvial soils. While the alluvial soils contain much transported organic matter, the older, well developed soils of around Lake Rumare will also contain significant organic matter developed over long periods from the established plant communities of the area. Well developed soil horizons are also found in this region. Therefore there is likely to be strong elluvial and illuvial horizons. Elluvial horizons are ones that have lost nutrients and particles to leaching processes. Illuvial horizons are horizons that have gained and accumulated these nutrients. Elluvial horizons directly overlay illuvial horizons and the nutrients once in the elluvial horizon are now in the illuvial horizon. A common soil profile for this region would look like this: A horizon (top layer, usually disturbed through plowing, contains fresh organic material yet to be lossed through leaching), E horizon (elluvial horizon), and then finally multiple B (illuvial horizons). The B horizons will have a significant clay increase and will almost certainly have redox features indicating the water table. This region, while less fertile than the lower parts of the Niben, is still well suited to agriculture. It is also well suited for infrastructure and roads.

All the soils of this region, and most of Cyrodiil, are Alfisols. Alfisols can occur generally in zones with a temperature range from below 0 oC to above 22 o C. Important for the development of Alfisols is the change between periods of high moisture content and high soil temperature, to break down the primary mineral components and to leach the weathered products, and low moisture content and low soil temperatures, which permit the precipitation or accumulation of the weathered products. Most Alfisols are formed under broadleaf deciduous forest, but they occur also under grassland and prairie vegetation. In forested ecosystems, the trees deliver the bulk of their annual production of organic matter aboveground, which is different from grassland soils. In those ecosystems the organic matter is enriched by the huge root system of the grass or prairie cover. In these soils, the B (illuvial) horizons begin somewhere around 18-30 cm. It is in these B horizons that the water table is usually found.

The soils of the Nibenay Valley are highly fertile and productive. The recent alluvium of the floodplains is the most productive but is not suitable for many types of infrastructure. The stream terraces and lands around Lake Rumare are also quite fertile and are fit for the construction of roads and structures. These are some of the most prime farmlands in the Empire and continued commercial agriculture is recommended in order to sustain the economy and feed the populace of Tamriel.