THERE are many changes for estimating erosion by water in RUSLE, the revised universal soil loss equation. The changes include the following:

Computerizing the algorithms to assist with the calculations.

New rainfall-runoff erosivity term values (R) in the western United States, based on more than 1,200 gauge locations.

Some revisions and additions for the eastern United States, including corrections for high R-factor areas with flat slopes to adjust for splash erosion associated with raindrops falling on ponded water.

Development of a seasonally variable soil erodibility term (K).

A subfactor approach for calculating the cover-management term (C), with the subfactors representing considerations of prior land use, crop canopy, surface cover, and surface roughness.

New slope length and steepness (LS) algorithms reflecting rill to interrill erosion ratios.

The capacity to calculate LS products for slopes of varying shape.

New conservation practice values (P) for rangelands, stripcrop rotations, contour factor values, and subsurface drainage.

History of the USLE 

Although the universal soil loss equation (USLE) is a powerful tool that is widely used by soil conservationists in the United States and many foreign countries, research and experience since the 1970s have provided improved technology that is incorporated in the …

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RUSLE: Revised universal soil loss equation

Agriculture and fishing are the primary source of almost all our food, as well as of many other products, so remain vital activities even though their share in the economy is small and in continuous decline. Partly for this reason public policy in these areas is almost entirely integrated at European level in the Common Agricultural Policy (CAP) and Common Fisheries Policy (CFP). Forestry policies are also heavily affected by EU-level decision-making. As agriculture dominates in terms of direct contribution to GDP and numbers of people engaged in it, as well as accounting for the largest amount of public support expenditure, it is agriculture that will receive the greatest attention here.

Agriculture, Forestry and Fisheries

Many models for soil water retention have been proposed. However, most of these models are curve-fitting equations and do not emphasize the physical significance of their empirical parameters. A new retention model that exhibits increased flexibility was developed by applying three-parameter lognormal distribution laws to the pore radius distribution function ƒ(r) and to the water capacity function, which was taken to be the pore capillary pressure distribution function ƒ(ψ). This model contains three parameters that are closely related to the statistics of ƒ(ψ): the bubbling pressure ψc, the mode ψ0 of ƒ(ψ) and the standard deviation σ of transformed ƒ(ψ). By comparison of this model with three existing models (the van Genuchten model, the Brooks-Corey model, and the modified Tani model), it was shown that ψc, ψ0, and σ are all essential for a general retention model.

Three-parameter lognormal distribution model for soil water retention

Event soil loss, runoff and the universal soil loss equation family of models: A review

From pedotransfer functions to soil inference systems

A Unifying Quantitative Analysis of Soil Texture

A unifying quantitative analysis of soil texture: Improvement of precision and extension of scale

Conventional soil texture classification systems use different definitions of particle-size distributions (PSDs). For example, sand in the International Soil Science Society (ISSS) system equals the combined separate limits of coarse silt and sand in the USDA system. Because relationships between texture and other soil properties are affected by these differences, the ability to merge survey data in environmental studies is limited. Previous research calculated two PSD statistics, namely the geometric mean particle diameter (dg) and its standard deviation (σg), which do not depend on separate limits. We expanded the development of the PSD statistics dg and σg to compare the USDA and ISSS systems, develop relationships with soil properties, include rock fragments, and simplify the USDA texture classification to facilitate the use of soil survey data in environmental research. We found that (i) for equal clay and sand fractions, the texture of a soil sample as described by the USDA system has larger dg and σg values than in ISSS; (ii) for equal clay and sand fractions, soil samples have larger values of cation-exchange capacity (CEC) in the ISSS than in the USDA system; (iii) small differences between some of the traditional 12 USDA classes are reflected in the dg and σg values for samples containing rocks, thereby presenting a rationale for simplification; and (iv) with this rationale, the 12 USDA classes were aggregated into five classes.

Particle-Size Distributions

Low soil water potential and low or high root temperatures are important stresses affecting carbon allocation in plants. This study examines the effects of these stresses on carbon allocation from the perspective of whole plant mass balance. Sixteen-day old spring wheat seedlings were placed in a growth room under precisely controlled root temperatures and soil water potentials. Five soil water potential treatments, from −0.03 MPa to −0.25 MPa, and six root temperature treatments, from 12 to 32°C were used. A mathematical model based on mass balance considerations was used, in combination with experimental measurements of rate of net photosynthesis, leaf area, and shoot/root dry masses to determine photosynthate allocation between shoot and root. Partitioning of photosynthates to roots was the lowest at 22–27°C root temperature regardless soil water potential, and increased at both lower and higher root temperatures. Partitioning of photosynthates to the roots increased with decreasing soil water potential. Under the most favourable conditions, i.e. at −0.03 MPa soil water potential and 27°C root temperature, the largest fraction, 57%, of photosynthates was allocated to the shoots. Under the most stressed conditions, i.e. at −0.25 MPa soil water potential and 32°C root temperature, the largest fraction, more than 80%, of photosynthates was allocated to roots.

L. Boersma

Papers

A Unifying Quantitative Analysis of Soil Texture

A unifying quantitative analysis of soil texture: Improvement of precision and extension of scale

Particle-Size Distributions

Partition of photosynthates between shoot and root in spring wheat (Triticum aestivum L.) as a function of soil water potential and root temperature

Evaluation of the Relationship between Compressibility and Shear Strength of Andisols