Orientador: Ely Nahas / Banca: Lucia Helena Sipauba Tavares / Banca: Elcio Liborio Balota / Resumo: A rotação de culturas é um processo de cultivo que pode modernizar e aumentar o rendimento da atividade agropecuária de forma sustentável agregando maior qualidade ao solo. Os objetivos deste estudo foram: (I) avaliar o efeito dos sistemas culturais em plantio direto conduzidos em rotação de culturas e monitorar as alterações das propriedades microbiológicas bioindicadoras da qualidade do solo; (II) investigar as mudanças bioquímicas nos solos decorrentes da adição de diferentes tamanhos de resíduos de soja e milho durante o período de incubação. Foram determinados as biomassas microbianas- C, N e P (CBM, NBM e PBM, respectivamente), a atividade respiratória (C-CO2) e das enzimas desidrogenase, fosfatase e urease, conteúdo do carbono orgânico (Corg), carbono solúvel (Csol), fósforo orgânico (Porg), matéria orgânica (MO), potencial de mineralização do N. O quociente metabólico (qCO2) e microbiano (qMIC) do solo foram calculados. Experimento (I): A avaliação foi realizada em amostras de solo coletadas após a colheita das culturas de verão do ano agrícola 2007/2008, na camada de 0-0,15 m de profundidade em um experimento conduzido sob sistema de semeadura direta, por seis anos. O delineamento experimental foi em blocos casualizados com esquema de faixas com três repetições. As sequências utilizadas foram as monoculturas de soja (Glycine max L.) (SS) e de milho (Zea mays L.) (MM) e a rotação de culturas soja/milho (SM). As culturas de inverno foram milho, girassol (Helianthus anuus L.), nabo forrageiro (Raphanus sativus L.), milheto (Pennisetum americanum (L.) Leeke), guandu (Cajanus cajan (L.) Millsp), sorgo (Sorghum bicolor (L.) Moench) e crotalária (Crotalária juncea L.). O conteúdo da biomassa microbiana-C, N e P do solo aumentou significativamente... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Crop rotation is a practice of growing dissimilar plants that can modernize and increase the farm economy in a sustainable form for adding more quality to the soil. The aims of this study were: (I) evaluate the effect of crop sequences under no-tillage systems on changes in the soil microbiological properties; (II) investigate the biochemistries changes during the incubation of the soil added with different sizes particles of soybean and corn. There were determined the contents of microbial biomass-C, N and P, the production of C-CO2, the activities of the enzymes dehydrogenase, urease and phosphatase, the organic carbon (Corg), soluble carbon (Csol), organic phosphorous (Porg) and organic matter (MO) contents and the potential of mineralization N. The soil metabolic (qCO2) and microbial (qMIC) quotients were calculated. Experiment (I): The evaluation was performed in soil samples collected after the summer crops harvest, on 2007/2008 growing season, at 0-0.15 m soil depth layer on an experiment conducted under no-tillage system through six years. The experimental had a completely randomized block design, in strips plots with three replications. The crop sequences were continuous soybean (Glycine max L.) (SS), continuous corn (Zea mays L.) (MM), and crop rotation soybean/corn (SM). Winter crops were corn, sunflower (Helianthus anuus L.), radish (Raphanus sativus L.), pearl millet (Pennisetum americanum (L.) Leeke), pigeon pea (Cajanus cajan (L.) Millsp), grain sorghum (Sorghum bicolor (L.) Moench) and sunn hemp (Crotalária juncea L.). The content of microbial biomass-C, N and P in the soil increased significantly in crop sequence SM compared to continuous crop. The interactions SM-millet and MMsorghum influenced the content of biomass-C, SM-hemp and SM-millet in the biomass-N content... (Summary complete electronic access click below) / Mestre

Orientador: Rogério Peres Soratto / Banca: Ciro Antonio Rosolem / Banca:Antonio Luiz Fancelli / Resumo: Com o aumento do cultivo de feijão no sistema plantio direto, torna-se necessário o conhecimento da reposta dessa cultura ao nitrogênio em solo sem preparo convencional por diferentes períodos de tempo, já que a disponibilidade desse nutriente pode ser alterada pelo sistema de manejo do solo. O objetivo foi avaliar o efeito da aplicação antecipada e/ou em cobertura do nitrogênio no feijoeiro cultivado em áreas com sistema plantio direto recém-implantado ou consolidado. O experimento foi conduzido durante o período "da seca", nos anos agrícolas 2007/08 e 2008/09, em um Nitossolo Vermelho, no município de Botucatu-SP. O delineamento experimental utilizado foi o de blocos casualizados em esquema de parcelas subdivididas, com quatro repetições. As parcelas foram representadas por quatro sistemas de manejo (SPDR: sistema plantio direto recém-implantado (a cultura do feijão será a primeira cultura a ser implantada no sistema de plantio direto); SPDC: sistema plantio direto consolidado (23 anos após a implantação); SPDR+N: sistema plantio direto recém-implantado com aplicação de 60 kg ha-1 de nitrogênio antecipado; SPDC+N: sistema plantio direto consolidado com aplicação de 60 kg ha-1 de nitrogênio antecipado). As subparcelas foram constituídas por quatro doses de nitrogênio em cobertura (0, 30, 60 e 120 kg ha-1). A adubação de cobertura foi efetuada no estádio fenológico V4, nos dois anos agrícolas. O tempo que a área permaneceu sob sistema plantio direto não influenciou a resposta do feijoeiro à adubação nitrogenada. A antecipação do N contribuiu para a manutenção da população de plantas almejada. A aplicação de N antecipado e em cobertura aumentou o número de vagens por planta, a massa dos grãos, o teor de proteína nos grãos e a produtividade de grãos do feijoeiro.Houve maior eficiência de uso do N quando este foi antecipado, do que quando... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: With the increase in common bean growth under no-tillage, it is necessary to know the response of this crop to nitrogen in soil without conventional tillage for different periods of time, since the availability of this nutrient can changed by the system of soil management. The aim of this study was to evaluate the effect of nitrogen early and/or sidedressed application for common bean crop, grown in newly implemented and established no-tillage system. The experiment was conducted during the dry period, in the 2007/08 and 2008/09 cropping seasons, on a Red Nitosol (Alfisol) located in Botucatu County, São Paulo State, Brazil. A randomized complete block design, in split-plot scheme, and four replications was used. The plots were composed by four management systems (NNT: newly implemented no-tillage system (common bean crop was the first to be cropped in no-tillage system); ENT: established no-tillage system (23 years without soil tillage); NNT+N: newly implemented notillage system with application of 60 kg ha-1 of nitrogen early at common bean sowing, and ENT+N established no-tillage system with application of 60 kg ha-1 of nitrogen early at common bean sowing). The subplots were composed by four sidedressed nitrogen doses (0, 30, 60, and 120 kg ha-1). The nitrogen sidedressing fertilization was performed in the V4 growth stage, in both cropping seasons. The time that area remained under no-tillage system did not influence the response of common bean plants to nitrogen fertilization. Nitrogen early application at common bean sowing contributed to maintaining the desired plant population. Nitrogen early and sidedressing application increased pods number per plant, grains weight,protein concentration in grains and grain yield of common bean. Nitrogen early application was more efficient than sidedressing application / Mestre

Resumo: O sistema de semeadura direta (SSD) proporciona melhores condições físicas do solo favorecendo o armazenamento de água no solo (ARM). A hipótese do trabalho foi que o Latossolo Vermelho argiloso, em sequências de culturas de verão e inverno sob SSD afeta o ARM em decorrência da modificação nos atributos físicos do solo e que o tensiômetro de punção digital (TDig) pode ser usado para medir o potencial mátrico da água no solo. Os objetivos foram avaliar o ARM e os atributos físicos do solo em sequências de culturas de verão e de inverno sob SSD e medir o potencial mátrico da água no solo por meio do tensiômetro de mercúrio e do TDig. O delineamento foi em blocos, com três repetições, no esquema em faixas. Os tratamentos foram constituídos por três sequências de culturas de verão (rotação soja/milho e monocultura de milho e soja) e sete culturas de inverno (milho, girassol, nabo forrageiro, milheto, guandu, sorgo e crotalária). Foram instalados tensiômetros nas camadas de 0,2; 0,4 e 0,6 m. Foi determinada a densidade do solo, a distribuição de poros por tamanho nas camadas de 0-0,1 e 0,1-0,2 m e a infiltração de água na superfície do solo. Os dados foram submetidos à análise de variância e as médias comparadas pelo teste de Tukey. O TDig pode ser usado para avaliar o potencial mátrico da água no solo. O ARM não diferiu entre as sequências de culturas de verão e nas culturas de inverno houve diferença, principalmente após período de menor disponibilidade hídrica. A densidade e a porosidade do solo não foram influenciadas pelas culturas de verão e inverno. O diâmetro de poros entre 0,075 - 0,05 e 0,03 - 0,0375 mm na camada de 0,0-0,1 m diferiu entre as sequências de verão. A distribuição de poros por tamanho não foi influenciada pelas sequências de culturas de inverno. A maior infiltração de água no solo ocorreu na parcela sob monocultura de soja / Abstract: No tillage system provides soil physical properties improvements, and soil water storage. The hypothesis of this study was that a Red Latosol (Oxisol), in summer and winter crops sequences under no-tillage system, can have its soil water storage influenced by changes in soil physical properties and digital tensiometer can be used to measure soil water matric potential. This study aimed to measure the soil matric potential using both mercury and digital tensiometers and to evaluate the soil water storage and physical properties on summer and winter crops sequences under no-tillage system. A completely randomized block was designed with three replications on a strips plan. The treatments were the combination of three summer crops sequences (soybean/maize rotation, corn and soybean monocultures) and seven winter crops (maize, sunflower, oilseed radish, millet, pigeon pea, sorghum and sunn hemp). Tensiometers were installed at a depth of 0.20; 0.40; 0.60 meters. Bulk density and pores distribution curves were determined from layers 0-0.1 and 0.1-0.2 depth and water infiltration at the soil surface. The data were submitted to variance analysis and means were compared by the Tukey test. The hypothesis was confirmed, therefore digital tensiometer can be used to measure soil water matric potential. The results showed no difference regarding soil water storage in summer crops sequences, especially after a period associated with lower water availability. Soil porosity and bulk density were not influenced by summer and winter crops sequences. The results indicated that the pores with diameter between 0,075 - 0,05 e 0,03 - 0,0375 mm from layer 0-0.1 m differed on summer crops sequences. No difference was observed by pores distribution curves between summer and winter crops sequences. The largest water infiltration occurred under the soybean monocultures plot / Orientador: José Eduardo Corá / Coorientadora: Carolina Fernandes / Banca: Antonio Evaldo Klar / Banca: Vilson Antonio Klein / Banca: Maria Helena Moraes / Banca: José Renato Zanini / Doutor

Orientador: Rafael Montanari / Resumo: A variabilidade espacial dos atributos físicos do solo é importante indicador de manejo localizado nas áreas agrosilvopastoris. No ano agrícola de 2009/10 em Selvíria (MS), analisaram-se os componentes de produção da soja e atributos físicos da relação massa/volume de um Latossolo Vermelho Distroférrico em plantio direto, com objetivo de encontrar correlações lineares e espaciais entre eles. Foi instalada uma malha geoestatística para a coleta dos dados, totalizando 99 pontos amostrais numa área de 10 ha. Os atributos do solo, nas camadas de 0,00-0,10 e 0,10-0,20 m foram: a densidade do solo, DS (métodos do anel volumétrico e do torrão parafinado), densidade de partículas do solo, DP (métodos do balão volumétrico e do balão volumétrico modificado) e a porosidade total do solo, PT, utilizando os valores de DS e DP dos diferentes métodos de determinação, calculada pela fórmula PT= (1-DS/DP). Os componentes de produção da soja foram: número de vagens por planta (NVP), número de grãos por vagem (NGV), massa de cem grãos (MCG), massa de grãos por planta (MGP), população de plantas (POP), altura de plantas (ALT) e produtividade de grãos obtida (PGO). Alguns dos componentes de produção da soja e dos atributos físicos do solo revelaram dependência espacial, possibilitando mapear a área de produção. Assim, os alcances geoestatísticos recomendados para futuras pesquisas deverão estar entre 273 e 526,5 m. Espacialmente, foi possível estimar a PGO pela co-krigagem com a MGP; com a DS (mé... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The soil physical attributes spatial variability is an important indicator of localized management practices in the agrosilvopastoral areas. In the 2009/2010 agricultural year in Selvíria (MS), soybean yield components and physical attributes of the mass/volume ratio of a dystroferric Red Latosol (Typic Acrustox) under a no-tillage system were analyzed in order to find linear and spatial correlations between them. It was installed a geostatistical grid to collect the data, totalizing 99 sampling points in an area of 10 ha. The soil attributes in the 0.00-0.10 and 0.10-0.20 m layers were: soil bulk density, BD (volumetric ring and paraffin sealed clod methods), soil particle density, PD (volumetric flask and modified volumetric flask methods) and total soil porosity, TP, calculated by the resulting ratio between BD and PD, using the formula TP = (1-BD/PD). The components of soybean yield were: number of pods per plant, number of grains per pod, mass of 100 grains, grain mass per plant, plant population, plant height and soybean yield. Some of the determined soybean yield components and some of the physical soil attributes revealed spatial dependence, making it possible to map the yield area. Thus, the recommended geostatistical ranges for further researches thus shall be between 273 and 526.5 m. Spatially, it was possible to estimate the soybean yield by co-kriging it with the grain mass per plant; and with the soil bulk density (volumetric ring method) of 0.00-0.10 m; and wit... (Complete abstract click electronic access below) / Doutor

O silício (Si) é benéfico ao desenvolvimento das plantas por proporcionar aumento na capacidade de defesa contra o ataque de pragas e de doenças, além de garantir porte ereto das plantas, o que aumenta a capacidade fotossintética dos vegetais. Fontes silicatadas, como silicatos de cálcio e de magnésio, fornecem Si ao solo e podem funcionar como corretivos de acidez. O acúmulo de resíduos vegetais e fertilizantes, mesmo no sistema semeadura direta (SSD), acelera o processo de acidificação do solo em curto prazo, principalmente em sua camada mais superficial. Esse processo é contínuo em solos tropicais úmidos e tem por consequência a baixa disponibilidade de nutrientes e elevados teores tóxicos de Al+3. Assim como no sistema convencional de manejo do solo, o SSD também demanda a aplicação de insumos, especialmente materiais corretivos de acidez. A aplicação de silicato pode interferir na disponibilidade de Si às plantas e nas formas desse elemento na solução do solo. O ácido silícico (H4SiO4) é a espécie de Si predominante em solos ácidos; e o aumento do pH pode causar sua desprotonação, gerando o ânion silicato (H3SiO4-). Estudos ligados ao Si em solos sob SSD são escassos, principalmente em experimentos de longa duração conduzidos sob condições de clima tropical úmido. Desde 2002 está sendo conduzido experimento de campo em um Latossolo Vermelho distroférrico sob SSD que recebeu aplicação superficial de calcário e de silicato de cálcio e de magnésio. Foram determinados os teores disponíveis de macronutrientes e silício, pH, soma de bases, saturação por bases, capacidade de troca catiônica, matéria orgânica, H+Al e Al3+, minerais silicatados e óxidos de Fe e Al, 24 meses após a reaplicação superficial dos corretivos. Foi feita especiação iônica de Al, Ca, Mg e Si em extrato aquoso e realizada a quantificação de Al por espectroscopia de ressonância magnética nuclear (27Al-NMR). Os principais óxidos encontrados foram a gibbsita, goethita e hematita. Diferentemente do Ca e do Mg, o Al não estava presente, em sua maioria, na forma livre Al3+, mas formando complexos com o carbono orgânico dissolvido. O silício estava quase que totalmente na forma de H4SiO4, sendo que a atividade dessa espécie foi semelhante à sua concentração em solução. A análise quantitativa de 27Al-NMR forneceu somente picos do complexo de alumínio hexa-hidratado ([Al(H2O)6]3+), não havendo espécies de alumínio complexadas com ácidos orgânicos. Amostras com teores moderados a alto de Al (27Al-NMR) se correlacionaram com as concentrações totais de Al provenientes da análise de espectroscopia de emissão atômica (ICP-AES). / Silicon (Si) is an element which is beneficial to plant development in that it provides a line of defense against attack by pests and disease as well, as ensure a plant posture that is more erect that increases their photosynthetic capacity. Silicon sources such as calciummagnesium silicates provide Si to the soil and act as acidity correctives. The accumulation of plant residues and fertilizers, even under a no-till system (NT), accelerates the process of soil acidification in the short term, especially in the uppermost surface layer. This process is continuous in moist tropical soils and results in a low level of nutrients and a high level of Al3+. As is the case under the conventional system of soil management, NT also requires the application of additives, especially acidity corrective materials. The application of silicate can interfere with the availability of Si to plants and the forms in which this element is found in soil solution. Silicic acid (H4SiO4) is the predominant form of Si found in acidic soils; and increases in the pH can cause deprotonation, which generates silicate anions (H3SiO4-). Studies related to Si in soils under NT are scarce, especially long-term experiments carried out under humid tropical conditions. Since 2002, a field experiment has been conducted on a dystroferric Oxisol under NT, where lime and calcium-magnesium silicate were surface applied. The contents of macronutrients and silicon available, as well as pH, basis total and basis saturation, cationic exchange capacity, organic matter, H+Al and Al3+, silicate minerals and Fe and Al oxides, were all determined 24 months after the correctives were applied. The ionic speciation of Al, Ca, Mg and Si took place in aqueous extract as well as the quantification of Al by nuclear magnetic resonance spectroscopy (27Al-NMR). The main oxides found were gibbsite, goethite and hematite. Unlike Ca and Mg, Al was not, for the most part, present in its free form Al3+ but complexed with dissolved organic carbon. Silicon was almost entirely in the form of H4SiO4, and its activity was similar to the concentration of this specie in solution. Quantitative analysis of 27Al-NMR has provided only peaks of Hexaaquaaluminium complex ([Al(H2O) 6]3+), with no species of organic-aluminum complexes. Samples with moderate to high levels of Al (27Al-NMR) were positively correlated with the total concentration of Al derived from the atomic emission spectroscopy analysis (ICP-AES).

Aggregate breakdown is an important process controlling the availability of fine soil material necessary for structural sealing of soil surfaces under rainfall. It may be caused by slaking resulting from rapid soil wetting and by physical dispersion resulting from direct and indirect energetic raindrop impacts. Relationships have been proposed by others predicting steady infiltration rate and saturated hydraulic conductivity from final aggregate size following high energy rainfall on initially dry, uncovered soil surfaces. Under these extreme conditions, both rapid wetting and energetic raindrop impact result in maximum aggregate breakdown and surface sealing. Knowledge of the relative importance of these two agents under less severe conditions and knowledge of how increased aggregate stability due to conservative soil management may ameliorate them should improve prediction and management of aggregate breakdown and surface sealing. ¶ This study has isolated and quantified effects of rapid soil wetting and energetic raindrop impact on aggregate breakdown and surface sealing. Simulated rainfall was applied to re-packed soils from differing tillage treatments on light textured soils from near Cowra and Condobolin in New South Wales, Australia. Aggregate breakdown was assessed using aggregate size distribution, determined by wet sieving and summarised by a range of statistics. The degree of breakdown was assessed after 66 mm of simulated rainfall whilst the rate of change in aggregate size distribution was assessed by sampling after 5, 10, 15, 30 and 60 mm. The degree of surface sealing was assessed using final surface hydraulic conductivity after 66 mm rainfall calculated from inferred infiltration and measured sub-seal soil water potential. The rate of surface sealing was assessed prior to ponding using cumulative rainfall volume at ponding and throughout the post-ponding phase by decline in surface hydraulic conductivity as a function of cumulative rainfall kinetic energy. Two levels of raindrop kinetic energy flux and three wetting treatments were used to isolate effects of these agents of aggregate breakdown and surface sealing. ¶ Significant surface aggregate breakdown was observed when either rapid soil wetting or highly energetic raindrop impact were allowed to occur. The majority of the data suggest a negative interaction between the two agents. When soil was initially dry rapid soil wetting was the dominant agent causing rapid aggregate breakdown, generally within the first 5 mm of rainfall. When rapid soil wetting was prevented by tension pre-wetting, energetic raindrop impact was the dominant agent and was able to cause aggregate breakdown of an almost equivalent degree. This breakdown occurred over a period lasting for up to 30 mm of rainfall. In contrast, the rate and degree of surface sealing were influenced primarily by raindrop kinetic energy with highly energetic impact leading to significant surface sealing, irrespective of soil wetting. For the soils studied, it was concluded that structural sealing of surface soil, could be significantly reduced by protecting the soil surface from energetic raindrop impact but that prevention of surface aggregate breakdown required amelioration of both processes. ¶ In addition to the negative interaction referred to above, a positive interaction was observed whereby energetic raindrop impact occurring concurrently with rapid soil wetting caused a greater degree of aggregate breakdown and a greater degree of surface sealing than energetic raindrop impact occurring subsequent to rapid soil wetting. The effect on surface sealing may be explained by the effect of lower sub-seal water potential that necessarily results from initially dry soil condition required for concurrent rapid wetting. However, the effect on aggregate breakdown remains unexplained. ¶ Notwithstanding the above, permeability was reduced under high kinetic energy rainfall even when soil wetting was reduced to very slow rates by tension pre-wetting. Likewise, surface sealing did occur under low kinetic energy rainfall for the least stable soil following rapid soil wetting. It was concluded that threshold soil wetting rates and threshold rainfall energy levels, proposed by others, are either not applicable to these soils or are negligible. ¶ The rate and degree of aggregate breakdown was also dependent on the soil with the Cowra soil being more stable than the Condobolin soil. Greater aggregate stability brought about by conservative tillage treatments at both soil locations retarded and reduced surface sealing. Unvalidated simulation modelling was used to illustrate possible effects for the soil water balance. In contrast to the conclusions of Loch (1994b), that were based on soils throughout eastern Queensland, the soil water balance simulations predicted that the residual benefits in ameliorating surface sealing resulting from improved aggregate stability could significantly reduce point runoff under the lower intensity winter rainfalls experienced in southern New South Wales. ¶ Limited testing with Condobolin soil following tension pre-wetting showed that rainfall intensity, varying over the range from 16.5 to 66 mm h-1, had little effect on the decline in surface hydraulic conductivity as a function of cumulative rainfall kinetic energy. This contrasts with greater seal permeability under higher rainfall intensities observed by Romkens et al. (1985) and others. It is proposed that an alternative explanation exists for the observations of Romkens et al. based on reduction in seal permeability due to lower sub-seal water potential under lower intensity rainfall. ¶ Post-ponding reduction in K[subscript sat] under high kinetic energy rainfall exhibited exponential decline as a function of cumulative raindrop kinetic energy as proposed by Moore (1981b). However, inferred rates of decline prior to ponding were more rapid than measured post-ponding rates suggesting that infiltration models using only a single exponential rate of surface K[subscript sat] decline based on post-ponding measurements may be in error. Potential for error is greatest at early times for loose soil that is highly susceptible to sealing. ¶ Pre-ponding decline in surface aggregation was also relatively more rapid than post-ponding decline. This discrepancy was evident irrespective of soil pre-wetting. From this it was concluded that the more rapid initial aggregate breakdown and surface sealing was due, at least in part, to processes other than aggregate slaking due to rapid soil wetting. An explanation has been proposed as follows. Raindrops initially fall on aggregates that have not been subjected to rainfall and therefore each drop has the capacity to cause greater aggregate breakdown than subsequent raindrops that fall on aggregates or soil fragments that have been strong enough to survive preceding rainfall impacts. Such a mechanism could provide an alternative explanation of the findings of Baumhardt et al. (1991) who found that less cumulative raindrop kinetic energy was necessary to achieve a given reduction in surface conductance when the cumulative energy was supplied through lower energy drops. ¶ Relationships predicting rates of surface sealing using aggregate breakdown under rainfall and aggregate stability were evaluated. Post-ponding infiltration rate and surface K[subscript sat] were related to aggregate size by exponential functions. The proportion of surface aggregates less than 0.125 mm in diameter provided slightly more consistent relationships. Parameters of fitted relationships differed among wetting pre-treatments suggesting that the influence of sub-seal water potential on surface K[subscript sat] must be considered whenever such relationships are developed or applied. Aggregate stability determined by wet sieving was related to rainfall volume required for ponding, final K[subscript sat] and final aggregate size but only for initially dry soil suggesting that such relationships may be unique to the rainfall, soils and flow conditions used to develop them. ¶ This study has established the relative importance of rapid soil wetting and energetic raindrop impact in both aggregate breakdown and surface sealing over a range of antecedent soil water and rainfall conditions. It has quantified the effectiveness of culturally induced aggregate stability in ameliorating effects of these two important agents and illustrated the potentially significant consequences for the soil water balance. It has quantified temporal patterns of surface sealing and aggregate breakdown and proposed an alternative mechanism explaining more rapid aggregate breakdown during the initial stages of rainfall. It has identified possible explanations for effects of rainfall intensity on surface sealing observed in other studies. It has also partially evaluated a mechanism proposed to explain important effects of subseal water potential on seal permeability found in this and other studies. These significant findings have been used with the findings of other studies to amend the conceptual model proposed by Le Bissonnias (1990). The amended model gives a more complete description of the relationships between parameters and processes determining aggregate breakdown and structural surface sealing under rainfall.

<p>Soils, in general, undergo both elastic and plastic deformations upon loading. Strain dependant anisotropic elasto-plastic models are required for realistic modeling for soil-tool mechanics that will address issues like stress history and soil anisotropy. Although several such models have been proposed, the science of coupled poro-mechanical analysis of an unsaturated soil has not been fully addressed.</p><p>Tillage tool modeling is primarily concerned with the analysis of soil deformation patterns and development of force prediction models for design optimization. Most of the models are based on quasi-static soil failure patterns that cause difficulty in accurately predicting soil-tool behaviour and soil forces for high speed operation. In recent years efforts have been made to improve the conventional analytical and experimental models by numerical approaches. Numerical simulations of soil-tool interactions using finite element modeling (FEM) and discrete element method (DEM) were mostly based on a solid mechanics approach. Due to limitations of constitutive relations, predictions of these numerical models have not been able to address tillage dynamics with high shear rates. The contribution of this research was to study the dynamics of soil-tool interaction using computational fluid dynamics (CFD) from the perspective of soil visco-plastic behavior.</p><p>A motorised soil rheometer was developed for evaluating soil visco-plastic parameters for CFD simulations. The apparatus was used to determine soil yield stress and viscosity at different soil moisture and compaction levels.</p><p>Three-dimensional CFD analyses were carried out using a commercial software CFX 4.4 to observe soil failure patterns around a tool and the pressure distribution on and around the tool. Duct flow as well as free-surface flow simulations of visco-plastic soil as a non-Newtonian Bingham material indicated soil deformation comprising of plastic flow and plug flow patterns. The soil failure front advancement demonstrated a critical speed range of 4 to 6.5 m s-1 where advancement of the failure front did not increase with speed. Soil pressure on the tool surface increased with the tool operating speed. Pressure distribution on the tool surface and draft requirement agreed well with the published literature based on experimental results and FEM analysis. The CFD approach, in its first attempt to tillage process, demonstrated its greater potential for dynamic modeling of soil-tool interaction.</p>

<p>Soils, in general, undergo both elastic and plastic deformations upon loading. Strain dependant anisotropic elasto-plastic models are required for realistic modeling for soil-tool mechanics that will address issues like stress history and soil anisotropy. Although several such models have been proposed, the science of coupled poro-mechanical analysis of an unsaturated soil has not been fully addressed.</p><p>Tillage tool modeling is primarily concerned with the analysis of soil deformation patterns and development of force prediction models for design optimization. Most of the models are based on quasi-static soil failure patterns that cause difficulty in accurately predicting soil-tool behaviour and soil forces for high speed operation. In recent years efforts have been made to improve the conventional analytical and experimental models by numerical approaches. Numerical simulations of soil-tool interactions using finite element modeling (FEM) and discrete element method (DEM) were mostly based on a solid mechanics approach. Due to limitations of constitutive relations, predictions of these numerical models have not been able to address tillage dynamics with high shear rates. The contribution of this research was to study the dynamics of soil-tool interaction using computational fluid dynamics (CFD) from the perspective of soil visco-plastic behavior.</p><p>A motorised soil rheometer was developed for evaluating soil visco-plastic parameters for CFD simulations. The apparatus was used to determine soil yield stress and viscosity at different soil moisture and compaction levels.</p><p>Three-dimensional CFD analyses were carried out using a commercial software CFX 4.4 to observe soil failure patterns around a tool and the pressure distribution on and around the tool. Duct flow as well as free-surface flow simulations of visco-plastic soil as a non-Newtonian Bingham material indicated soil deformation comprising of plastic flow and plug flow patterns. The soil failure front advancement demonstrated a critical speed range of 4 to 6.5 m s-1 where advancement of the failure front did not increase with speed. Soil pressure on the tool surface increased with the tool operating speed. Pressure distribution on the tool surface and draft requirement agreed well with the published literature based on experimental results and FEM analysis. The CFD approach, in its first attempt to tillage process, demonstrated its greater potential for dynamic modeling of soil-tool interaction.</p>

Rice and maize are global staple food and play an important role in world’s food security strategy. Vietnam is one of rice leading export countries but annually it has to import a considerate amount of maize for cattle food processing. Red River Delta in the north of Vietnam is the second rice bucket of the country, which is responsible formore than 20% of total rice production. The priority crops in the areas are rice and maize and rice-maize system is the leading cropping system in the area. Currently, it is reported that the rice-maize cropping system is not sustainable and its profit is reducing in most of production areas in the Red River Delta. Improving rice cropping system aims is not only to increase rice and maize yields and production but also to improve the land use efficiency, decline the cost of the production and to increase system sustainability. To increase sustainability there must be a linkage of various factors. This review emphasizes on increasing rice-maize crop sustainability by applying appropriate agriculture practices such as reducing chemical fertilization and intensive tillage. / Gạo và ngô là nguồn lương thực chính cho toàn cầu và đóng một vai trò quan trọng trong chiến lược an ninh lương thực của thế giới. Việt Nam là một trong những nước dẫn đầu về xuất khẩu gạo nhưng hàng năm vẫn phải nhập một số lượng lớn ngô để chế biến thức ăn gia súc. Đồng bằng sông Hồng là một trong hai vựa lúa lớn của Việt Nam sản xuất khoảng 20% sản lượng lúa gạo của cả nước. Ở đồng bằng sông Hồng, lúa và ngô là hai cây trồng chính là hệ canh tác lúa-ngô là cơ cấu cây trồng hàng đầu trong vùng. Tuy nhiên, trong những năm gần đây, rất nhiều đánh giá cho thấy hệ thống canh tác lúa-ngô là hệ thống canh tác không bền vững và các lợi nhuận của mang lại từ cơ cấu canh tác ở hầu hết các khu vực sản xuất ở vùng đồng bằng sông Hồng của Việt Nam đã và đang giảm dần. Do đó, việc cải thiện cơ cấu canh tác lúa-ngô không chỉ nhằm mục đích tăng năng suất lúa và ngô mà còn nâng cao hiệu quả sử dụng đất, giảm chi phí sản xuất và tăng cường hệ thống canh tác bền vững. Tuy nhiên, để tăng tính bền vững của hệ thống canh tác thì phải liên kết nhiều yếu tố khác nhau. Bài viết này dựa vào các kết quả nghiên cứu của các tác giả khác nhau để đưa ra những giải pháp tích cực làm tăng tính bền vững của hệ thống canh tác lúa-ngô bằng cách áp dụng các phương pháp canh tác hợp lý như giảm sử dụng phân hóa học và các biện pháp canh tác thâm canh như áp dụng phương pháp làm đất tối thiểu.

The main purpose of this study was to evaluate the effect of alternative cropping systems on farm net returns, and nitrate-N and sediment yields in Thomas Brook Watershed (TBW). The study involved integrated bio-physical and economic optimization modelling. Crop yield and nitrate-N pollution response functions were estimated and then used in trade-off analysis between farm returns and environmental quality improvement. Five crop rotation systems were evaluated for seven fertilizer levels under conventional tillage (CT) and no-till systems (NT). Nitrate-N leached, as well as estimated maximum economic rate of N (MERN) fertilizer level and marginal abatement costs depended on crop type, rotation system, and tillage type. The most cost effective cropping systems that met restrictions on Health Canada maximum limit on nitrate-N in water included corn-corn-corn-alfalfa-alfalfa under NT for corn-based cropping systems, potato-winter wheat-carrot-corn under CT for vegetable horticulture-based and potato-barley-winter wheat-potato-corn under NT for potato-based cropping systems.