User:Hansh07/sandbox

Soil loss tolerance
The greatest allowable degree of soil loss from an area that allows a high level of production to be maintained is known as soil loss tolerance. It is usually used to determine if a soil is exposed to erosion risk (soil erosion), productivity loss, and off-site damages. Soil loss tolerance is also known as T value which is in unit of tons per acre per year. The soil loss tolerance levels range from 1 to 5 in which show the maximum amount of soil loss per acre per year that may be tolerated for growing food, feed, and fibre plants. 1 ton/ac/year is usually for the most fragile soils, and 5 tons/ac/year is for soil that could sustain more erosion without losing significant productive potential.

Texture, permeability, accessible water capacity, and depth to restrictive layers like as rock, clay, or gravel are all factors that influence T value.

History of soil loss tolerance
Soil loss tolerance is determined based on over 80 years of research establishing rates of soil formation and the effects of erosion on soil productivity. The idea was firstly stated in 1941 that soil loss values could be affected by the possibility to damage soil with fertilizers to replace nutrient content loss from erosion. The concept was subsequently spreaded and applied since 1962, when the T value were determined by U.S. Soil Conservation Service for the majority of the American soil types with assigned value range from 4.5 to 11.2 ton ha–1 year–1. Now the range has adjusted to 1-5 ton ha–1 year–1 which is same as the range in Europe which was decided in 1998.

Evaluation of soil loss tolerance
Soil loss tolerance (T value) is an effective tool for planning soil and water conservation projects worldwide as it is applicable for converting both technical and nontechnical elements into a number. The commonly accepted maximum limit of soil loss is 277 Mg ac–1 year–1.

The relationship between soil loss tolerance and soil depth is expressed as:

T (x, y, t) = (T1 + T2)/2 - (T2-T1) / 2 cos (π(Z-Z1) / (Z2-Z1))

where T (x, y, t) is the T value at point (x, y) at time t (i.e., the present), T 1 is the lower limit of T, T 2 is the upper limit of T, Z is the present soil depth, Z 1 is the minimum allowable soil depth, and Z 2 is the optimum soil depth.

The universal soil loss equation (USLE) could be applied for TSL value to design for soil and water systems conservation projects. The T values obtained from USLE are not relevant to building sites or other non-farm applications.

Soil loss tolerance (T values) for different types of land
Ecological service-related characteristics such as organic matter content, soil formation rates, erosion rates, and pollution offset could be chosen as factors influencing T in forests and grasslands. T values in these places can be calculated using the soil formation rate or the erosion rate. The T value standard should be greater in forests and grasslands than in agriculture. As for the soils in particular regions such as significant mining and industrial regions, key natural reserves, and watersheds may represent a risk to people's health and well-being. As a result, estimating the T values for certain soils should take pollution, water quality, and erosion rate into account, among other variables. In such cases, the greatest T values would be preferable in order to better regulate the erosion modulus through soil and water conservation projects (both biological and engineering).

In terms of farmland, Soil productivity-related elements such as soil depth, soil fertility, gully formation management, and water losses are chosen as variables impacting T values in agricultural perspective, and T values should be evaluated using soil productivity-based methodologies. Furthermore, soil productivity can differ substantially depending on the types of soil, climate, and topography. Hence, evaluating T value in farmland occurred to be the most complex and difficult.

Future research for Soil loss tolerance
It was indicated that the soil loss tolerance established in U.S. soils could not be suitable for soils in other regions due to the poorly and outdated scientific evidence. There are many questions remained to be answered such as planning periods and offset damages should also be included in calculating T values.