Carbon pool ratios as scientific support to field morphology in the differentiation of dark subsurface soil horizons

In soil surveys, it is usual to find profiles with an uncommon disposition of horizons. Dark horizons in depth might be either the consequence of erosion and redeposition of soil materials from upslope or an indication of the podzolization process, which forms a spodic horizon. Few laboratory analyses are known to characterize dark subsurface horizons which could allow for the differentiation of spodic from buried A horizons. Some researchers propose C-humic and C-fulvic acid fraction ratios and forms of carbon to analyze characteristics of these horizons. Therefore, this research aimed to characterize dark subsurface horizons found in soils under a Eucalyptus minimum tillage system in the state of Rio Grande do Sul, Brazil, and to relate soil organic carbon to landscape features in toposequences. The characterization was performed by using the following ratios: humic acid and fulvic acid fractions (Cha/Cfa); pyrophosphate extractable-C and organic carbon (Cp/OC); fulvic acid fraction and pyrophosphate extractable-C (Cfa/Cp), and fulvic acid fraction and organic carbon (Cfa/OC). Soil organic carbon was related to slope gradient and Geomorphons in a Geographic Information System (GIS). None of the horizons analyzed met the criteria required for spodic horizon classification, where Cha/Cfa < 0.50, Cfa/OC < 0.30, and the ratio Cp/OC ≥ 0.50 simultaneously with Cfa/Cp ≥ 0.50. A relationship was found between landscape features and soil organic carbon content. The methodology proved to be satisfactory for providing scientific support to field morphology classification of dark subsurface horizons, specifically in the case where they could be misinterpreted as spodic horizons

Índice de cobertura vegetal pela cultura do milho no período de chuvas intensas no sul de Minas Gerais Plant cover index in the period of intensive rainfall for corn crop at south of Minas Gerais state, Brazil

A cobertura vegetal é a defesa natural do solo contra a erosão hídrica. Nos modelos de estimativas de perdas de solo, o efeito da cobertura vegetal na interceptação da energia cinética da chuva é a variável chave na modelagem do processo erosivo. Assim sendo, objetivou-se avaliar a eficiência da cobertura vegetal, proporcionada pela cultura do milho, e suas relações com os atributos fitotécnicos desta cultura para alguns híbridos. O estudo foi realizado no campo demonstrativo de híbridos de milho da Universidade Federal de Lavras, localizada no município de Lavras, MG. Para determinação da cobertura vegetal utilizou-se um aparato que consiste em uma estrutura horizontal, contendo orifícios para visualização dos pontos com cobertura e sem cobertura vegetal, sendo as leituras feitas de forma aleatória e transversalmente às linhas da cultura. Os atributos fitotécnicos avaliados foram altura da planta, estande, matéria seca e produção de grãos. Diante dos resultados pode-se concluir que o maior índice de cobertura vegetal foi observado para os híbridos de milho P 30F33, P 30F90, P 3021, STRIKE, FORT, VALENT, UFLA 2001, UFLA 2004, CO 32, D 8480, D 8420 DKB 333B, DKB 440, evidenciando boa qualidade como planta protetora do solo. No período de maior ocorrência de chuvas, na região sul de Minas Gerais, a cultura do milho pode minimizar o efeito do processo erosivo. A produção de matéria seca relacionou-se bem com o índice de cobertura vegetal, podendo ser um indicativo quanto à proteção do solo.<br>The plant cover is a natural protection of soil against water erosion. In estimative models of soil loss, the effect of plant cover in the interception of rainfall kinetic energy is the key variable in the modeling of the erosive process. Thus, the aim of this work is to evaluate the efficiency of the plant cover provided by the corn crop and their relations with the phytotechnical attributes of this crop for its respective hybrids. This study was conducted in the corn hybrids demonstrative field at the Federal University of Lavras, Minas Gerais State, Brazil. In order to evaluate the plant cover a display was used that included a horizontal structure, containing holes for viewing the points with and without plant cover, the being readings performed at random and transversally to the crop lines. The phytotechnical attributes evaluated were plant height, stand, dry matter and grain production. It can be concluded that the higher plant cover index was observed for corn hybrids P 30F33, P 30F90, P 3021, STRIKE, FORT, VALENT, UFLA 2001, UFLA 2004, CO 32, D 8480, D 8420 DKB 333B, and DKB 440, proving good quality as a protective soil plant. In the period of larger occurrence of rainfall in the south of Minas Gerais state, the corn crop can minimize the effect of the erosive process. The production of dry matter was well correlated with the plant cover index, and can be used as evidence of soil protection

Perdas de solo, água, nutrientes e carbono orgânico em Cambissolo e Latossolo sob chuva natural Soil, water, nutrients and organic carbon losses from inceptisol and Oxisol under natural rainfall

A erosão hídrica é responsável por perdas de nutrientes e carbono dos solos agrícolas. A minimização das perdas de solo, água, nutrientes e carbono orgânico constitui importante aspecto do planejamento conservacionista. Os objetivos deste trabalho foram avaliar as perdas, por erosão hídrica, de solo, água, nutrientes e carbono orgânico em Cambissolo Háplico Tb distrófico típico (CXbd) e Latossolo Vermelho distroférrico típico (LVdf). As coletas foram realizadas depois de cada evento de chuva considerada erosiva. As perdas médias anuais de solo foram de 205,65 Mg ha-1 para o CXbd e de 14,90 Mg ha-1 para o LVdf. As perdas médias anuais de água foram 369 mm para o CXbd e 113 mm para o LVdf, representando, respectivamente, 28,67% e 8,78% do total precipitado. Os atributos mineralógicos, químicos e físicos e o relevo de ocorrência desses solos explicam satisfatoriamente os resultados obtidos. O CXbd apresentou as maiores perdas de nutrientes e carbono orgânico. O carbono orgânico foi encontrado em maior quantidade no sedimento erodido, evidenciado pelo caráter seletivo da erosão.<br>Water erosion is responsible for considerable losses of nutrients and organic carbon from agricultural soils. The reduction of soil, water, nutrients and organic carbon losses constitutes an important aspect of the conservation planning. The objectives of this work were to evaluate the soil, water, nutrients and organic carbon losses from a Typic Dystrochept (TD) and a Rhodic Hapludox (RH). The samplings were performed after each considered erosive rain event. The mean annual soil losses were 205.65 Mg ha-1 for the TD and 14.90 Mg ha-1 for the RH. The mean annual water losses were 369 mm for the TD and 113 mm for the RH, representing 28.67% and 8.78% of the total precipitation, respectively. The mineralogical, chemical and physical attributes and the relief where these soils occur satisfactorily explain the obtained results. The TD presents higher nutrients and organic carbon losses than the RH. The organic carbon was the main component of the eroded sediment, evidenced by the selective character of erosion