Reconsolidation of the soil surface after tillage discontinuity, with and without cultivation, related to erosion and its prediction with RUSLE

Abstract

Site-specific regression coefficient values are essential for erosion prediction with empirical models. With the objective to investigate the surface-soilconsolidation factor, Cf, linked to the RUSLE's prior-land-use subfactor, PLU, an erosion experiment using simulated rainfall on a 0.075 m m-1 slope, sandy loam Paleudult soil, was conducted at the Agriculture Experimental Station of the Federal University of Rio Grande do Sul (EEA/UFRGS), in Eldorado do Sul, State of Rio Grande do Sul, Brazil. Firstly, a row-cropped area was excluded from cultivation (March 1995), the existing crop residue removed from the field, and the soil kept clean-tilled the rest of the year (to get a degraded soil condition for the intended purpose of this research). The soil was then conventional-tilled for the last time (except for a standard plot which was kept continuously cleantilled for comparison purposes), in January 1996, and the following treatments were established and evaluated for soil reconsolidation and soil erosion until May 1998, on duplicated 3.5 x 11.0 m erosion plots: (a) fresh-tilled soil, continuously in clean-tilled fallow (unit plot); (b) reconsolidating soil without cultivation; and (c) reconsolidating soil with cultivation (a crop sequence of three corn- and two black oats cycles, continuously in no-till, removing the crop residues after each harvest for rainfall application and redistributing them on the site after that). Simulated rainfall was applied with a Swanson's type, rotating-boom rainfall simulator, at 63.5 mm h-1 intensity and 90 min duration, six times during the two-and-half years of experimental period (at the beginning of the study and after each crop harvest, with the soil in the unit plot being retilled before each rainfall test). The soil-surface-consolidation factor, Cf, was calculated by dividing soil loss values from the reconsolidating soil treatments by the average value from the fresh-tilled soil treatment (unit plot). Non-linear regression was used to fit the Cf = e b.t model through the calculated Cf-data, where t is time in days since last tillage. Values for b were -0.0020 for the reconsolidating soil without cultivation and -0.0031 for the one with cultivation, yielding Cf-values equal to 0.16 and 0.06, respectively, after two-and-half years of tillage discontinuation, compared to 1.0 for fresh-tilled soil. These estimated Cf-values correspond, respectively, to soil loss reductions of 84 and 94 %, in relation to soil loss from the fresh-tilled soil, showing that the soil surface reconsolidated intenser with cultivation than without it. Two distinct treatmentinherent soil surface conditions probably influenced the rapid decay-rate of Cf values in this study, but, as a matter of a fact, they were part of the real environmental field conditions. Cf-factor curves presented in this paper are therefore useful for predicting erosion with RUSLE, but their application is restricted to situations where both soil type and particular soil surface condition are similar to the ones investigate in this study.

Soil, water, nutrients and soil organic matter losses by water erosion as a function of soil management in the Posses sub-watershed, Extrema, Minas Gerais, Brazil

“…Similar behavior was observed by Cogo and Streck (2003), Streck and Cogo (2003), Volk et al (2004), Castro et al (2006) and Gilles et al (2009) in studies on the effects of vegetation cover and soil management on soil erosion. The authors attributed the increased surface flow (higher water loss) to the increased consolidation of the soil surface in more conservationist systems, when compared with the conventional ones.…”

Hidrogramas e sedimentogramas associados à erosão hídrica em solo cultivado com diferentes sequências culturais, com diferentes condições físicas na superfície

“…Já as superfícies de solo que se encontravam mobilizadas, portanto com média e grande rugosidade (1,13 a 1,76 cm) -também média e grande porosidade total da camada preparada do solo -, atuaram de modo inverso, com variada, porém sempre pequena influência da cobertura por resíduos culturais. Resultados semelhantes foram obtidos por vários outros pesquisadores em estudos de natureza semelhante à deste (Burwell & Larson,1969;Larson & Gill, 1973;Cogo et al, 1984;Norton et al, 1985;1987;Schick et al, 2000;Streck & Cogo, 2003;Volk et al, 2004). Quanto às diferenças nos hidrogramas, motivadas pelos tratamentos de sequência cultural, de modo geral foram maiores no primeiro (T1), no quarto (T4) e no sexto (T6) teste de erosão (respectivamente, Figuras 1a a 1e, 2f a 2j e 3f a 3j), destacando-se aqueles com a sequência envolvendo teosinto como os de menor magnitude (Figuras 1b, 2g e 3g), seguidos pelos com as sequências envolvendo milho+feijão-miúdo e milheto (respectivamente, Figuras 1d, 2i e 3i e 1c, 2h e 3h), os quais diferenciaram pouco entre si.…”

Chuvas intensas relacionadas à erosão hídrica

“…Em geral, um solo com estrutura de boa qualidade apresenta boa capacidade de retenção, infiltração, permeabilidade e armazenamento de água no seu interior, o que, no conjunto, refletirá em menor erodibilidade (Volk et al, 2004). Em estudos dessa natureza, Streck & Cogo (2003) observaram que a estabilidade de agregados tende a aumentar em solos cultivados com plantas que produzem elevada massa de raízes variando, no entanto, com a espécie vegetal, de acordo com as diferenças existentes na morfologia e distribuição de volume das raízes.…”