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Adequate soil management can create favorable conditions to reduce erosion and water runoff, consequently increase water soil recharge. Among management systems intercropping is highly used, especially for medium and small farmers. It is a system where two or more crops with different architectures and vegetative cycles are explored simultaneously at the same location. This research investigated the effects of maize intercropped with jack bean on soil losses due to water erosion, estimate C factor of Universal Soil Losses Equation (USLE) and how it can be affected by soil coverage. The results obtained also contribute to database generation, important to model and estimate soil erosion. Total soil loss by erosion caused by natural rain, at Lavras, Minas Gerais, Brazil, were: 4.20, 1.86, 1.38 and 1.14 Mg ha -1 , respectively, for bare soil, maize, jack bean and the intercropping of both species, during evaluated period. Values of C factor of USLE were: 0.039, 0.054 and 0.077 Mg ha Mg -1 ha -1 for maize, jack bean and intercropping between both crops, respectively. Maize presented lower vegetation cover index, followed by jack beans and consortium of the studied species. Intercropping between species showed greater potential on soil erosion control, since its cultivation resulted in lower soil losses than single crops cultivation, and this aspect is really important for small and medium farmers in the studied region. Index terms:Cover plants, C factor, soil sustainability. RESUMOO manejo adequado do solo pode criar condições favoráveis para reduzir a erosão hídrica e escoamento superficial, e, consequentemente, aumentar a recarga de água no solo. Entre os sistemas de manejo, o consórcio de culturas é um sistema de manejo muita utilizado, principalmente por médios e pequenos agricultores. Trata-se de um sistema onde duas ou mais culturas com diferentes ciclos e arquiteturas vegetativas são exploradas concomitantemente, no mesmo local. Portanto, objetivou-se neste trabalho, avaliar os efeitos do consórcio entre a cultura do milho e o feijão-de-porco nas perdas de solo por erosão hídrica, a determinação do fator C da Equação Universal de Perda de Solo (EUPS) e do índice de cobertura para os sistemas de cultivos estudados. Pode-se concluir que as perdas de solo totais por erosão hídrica sob chuva natural, no município de Lavras, MG, foram de 4,20, 1,86, 1,38 e 1,14 Mg ha -1 , respectivamente, para o solo descoberto, milho, feijão-de-porco e o consórcio entre as duas espécies, durante o período avaliado. Os valores de fator C da EUPS calculados para os diferentes sistemas de cultivos foram 0,039, 0,054 e 0,077 Mg ha Mg -1 ha -1 para o milho, feijão-de-porco e o consórcio entre as duas espécies, respectivamente. O plantio do milho solteiro apresentou menor índice de cobertura vegetal, seguido do cultivo de feijão-de-porco solteiro e do consórcio entre as duas espécies vegetais. O consórcio entre as espécies apresentou maior potencial no controle de processos erosivos, uma vez que seu cultivo resulta em menores p...

Recebido em 19/8/09; aceito em 28/7/10; publicado na web em 16/11/10 SURFACE CHARGE OF CLAY FRACTION AS AFFECTED BY VINASSE AND PHOSPHORUS. Effects of vinasse, P sorption and the interaction vinasse-phosphorus on zeta potential and point of zero charge (PZC) as well as the effects of vinasse on P sorption on clay-fraction samples from two soils were evaluated. The vinasse and P sorption influenced the surface charge of clay fraction of both soils. Sorption of P increased negative charges from soil particles reducing PZC. These effects were more pronounced when clay fraction was previously treated with vinasse. Vinasse treatment reduced P sorption, probably due to coating of P-adsorption sites and by enhancing the negative charges.Keywords: zeta potential; point of zero charge (PZC); soil charges. INTRODUÇÃOAs cargas na superfície das partículas dos solos estão relacionadas aos fenômenos de superfície, como a dispersão/floculação, 1,2 capacidade de troca de cátions e de ânions, 3 adsorção de pesticidas 4 e de metais pesados. 5 As cargas do solo podem ser do tipo permanente, quando originadas de substituição isomórfica na formação dos minerais, principalmente da fração argila, ou dependentes do pH do meio (variáveis), 6,7 sendo essas últimas comuns em solos tropicais altamente intemperizados ricos em óxidos de ferro e de alumínio. 8 As cargas variáveis representam mais de 70% da carga total em amostras da superfície de Latossolos. 9Uma das formas de avaliar as cargas superficiais dos coloides do solo é por meio do potencial zeta (ζ), definido como a carga elétrica líquida que se desenvolve no plano que divide a camada de Stern e a camada difusa a um determinado pH.6 O ζ é influenciado principalmente pela concentração eletrolítica e pelo pH da suspensão coloidal. 6,10,11 Quando o ζ é igual a zero, o ponto de carga zero (PCZ) da partícula coloidal é alcançado. 6 A carga elétrica e o PCZ são dependentes da proporção dos constituintes minerais e orgânicos do solo. Os óxidos de ferro e de alumínio contribuem para o aumento das cargas positivas e do PCZ, enquanto a matéria orgânica e argilominerais silicatados, como a caulinita, aumentam as cargas negativas e reduzem o PCZ.3,12-14 Além disso, a introdução de cátions, ânions e moléculas no meio podem afetar reações de protonação/desprotonação, influenciando as cargas superficiais e o PCZ dos coloides do solo. [15][16][17] Solos ricos em óxidos de ferro e de alumínio apresentam elevada adsorção de P, 18-20 exigindo adubações pesadas desse nutriente para se ter uma disponibilidade adequada para as plantas. Além de sua elevada adsorção, o P causa significativas mudanças nas cargas superficiais das partículas do solo, tornando-as mais eletronegativas e reduzindo o PCZ. 16,17,21 Tais alterações, além dos benefícios da adubação fosfatada, podem contribuir para o aumento da capacidade de troca de cátions no solo, 3 importante no manejo da fertilidade do solo e, também, influenciar o comportamento sortivo de metais pesados e pesticidas.22,23 Por outro lado, o aumento da carga lí...

Several soil conservation practices are used to reduce water erosion and ensure sustainable agriculture. An effective crop management practice is intercropping, in which two or more crops with different architectures and vegetative cycles are grown simultaneously in the same area. We hypothesized that intercropping of corn and jack-bean increases soil cover and reduce soil erosion by water in comparison to monocropping. The objective of this study was to evaluate the effects of different crop systems on soil cover and on soil erosion by water. Soil and water losses from a Typic Hapludox were measured under the following systems: corn cultivation (CO), jack-bean cultivation (JB), intercropping of corn and jack-bean (IC), and bare soil (BS), as a reference for maximum erosion rates. For each crop system, erosion plots with dimensions of 12 × 4 m were set up in the field on a 0.12 m m -1 slope gradient. The experiment was carried out under natural rainfall, over three crop seasons (November to March) from 2011 to 2014. The soil cover index of the systems was monitored during crop growth, and rainfall erosivity for the crop seasons was calculated according to the EI 30 index to interpret soil and water losses. A set of linear mixed models was fitted to relate soil losses to rainfall erosivity, crop systems, and soil cover. The average rainfall erosivity in the study area was 6,132 MJ mm ha -1 h -1 per crop season. The results indicate that water losses are directly related to erosivity and are less influenced by soil cover and cultivation systems than the soil losses. A linear maximum value of the soil cover index was achieved 70 days after sowing. Intercropping exhibited greater soil cover than single crops. Total soil losses from the three seasons display the trend: BS > CO > JB > IC. The best fitted model of the linear mixed models indicates that soil loss responses are strongly correlated with rainfall erosivity and soil cover, which nullified the influence of the crop systems in the model.

In order to assess the movement of trifluralin in soils, used as root intrusion inhibitor in subsurface drip irrigation system (SDI), its concentration at effluent from lysimeters was measured. The lysimeters with sugarcane (Sacharum officinarum L.) under natural weather conditions and supplementary irrigation were filled with two Oxisols and an Ultisol. Three lysimeters with undisturbed soil were used as replicates for each treatment; the columns were one meter in diameter and 45cm deep. The SDI system consisted of drippers installed at 20cm depth, with 10.5mm internal diameter tubing with 6 emitters per lysimeter spaced 50cm between them. A moisture sensor was installed in each lysimeter to monitor the soil water tension. A weather station was installed besides the lysimeters, in order to supply weather information. Precipitation, volume of leachate, and trifluralin concentration in the effluent were measured during 65 days. There was no change on the SDI system flow rate. The LVA presented the highest amounts of leached compound, which was above the EPA limit and lower than the allowed by Brazilian law.