To date only a limited number of studies have been done at the field level to observe the effects of agricultural management practices on carbon sequestration, water quality, and bioenergy crop yield in Mississippi. Therefore, the goals of this study were to monitor soil organic carbon (SOC) levels at the field scale and perform a comprehensive analysis of the potential environmental impacts at the watershed scale using the Soil and Water Assessment Tool (SWAT) in two watersheds located in Mississippi. It was found that SOC levels generally are affected by depth, land use, and time. The SWAT models showed good performance overall and predicted that perennial grass production in the Town Creek watershed would render the most feedstock with the least environmental impact. The results of this study were consistent with the available literature, but a longer study period is recommended.

Deep row incorporation (DRI) is a biosolids recycling method that is especially appropriate for reclaiming disturbed land because of the extremely high application rates used. Nutrient additions in excess of the vegetation requirements, especially in coarse-textured soils, can potentially impair water quality. Increasing C and N additions with biosolids DRI can also generate emissions of greenhouse gases N₂O and CH₄ and decrease the value of C sequestration. Objectives of this research were: (i) compare the effects of DRI biosolids type and rate and annual conventional fertilizer application on N and P leaching losses; (ii) determine the effects of aging on the N, C and P dynamics in the DRI biosolids seams; (iii) compare the effects of biosolids type and conventional N fertilization on N₂O, CH₄ and CO₂ emissions; and (iv) compare the effects of DRI biosolids and conventional N fertilization on hybrid poplar biomass dynamics, C, N and P sequestration. The following eight treatments were established to achieve objectives (i) and (iv): 0 (control), 167, 337, 504 kg N ha⁻¹ yr⁻¹ as conventional fertilizer; 213 and 426 Mg ha⁻¹ anaerobically digested (AD) and 328 and 656 Mg ha⁻¹ lime stabilized (LS) biosolids applied in trenches. The amount of N lost from the DRI biosolids was 261–803 kg N ha⁻¹, while the fertilizer treatments were not different from 0 kg N ha⁻¹ yr⁻¹ control. Orthophosphate and TKP leached in negligible amounts. Deep row biosolids incorporation did not pose P leaching risks but did result in high N leaching below the biosolids seams. Aboveground biomass production in the biosolids treatments was not different from the control treatment and ranged from 2.1±0.3 to 4.0±0.5 kg tree⁻¹. The fertilizer treatments produced significantly less biomass than the control and the biosolids treatments. Hybrid poplars sequestered up to 3.20±0.54 Mg C ha⁻¹, 71±12 kg N ha⁻¹, and 11.0±1.8 kg P ha⁻¹. The planting density capable of the N uptake in order to avoid N leaching was estimated at 3912 to 11363 trees ha⁻¹. Our results suggest increased hybrid poplar planting density and decreased application rates of DRI biosolids may decrease the risk of groundwater contamination with N. Three treatments were compared to address objective (ii): 426 Mg ha⁻¹ AD and 656 Mg ha⁻¹ LS biosolids. Organic C losses were 81 Mg ha⁻¹ and 33 Mg ha⁻¹ for LS and AD biosolids, respectively. Total N lost over the course of two years was 15.2 Mg ha⁻¹ and 10.9 Mg ha⁻¹ for LS and AD biosolids, respectively, which was roughly 50% of the N applied. No significant losses of P were detected. Most of the P was Al- and Fe-bound in the AD biosolids and Ca-bound in the LS biosolids. Our results indicated that recommended rates of DRI biosolids in coarse textured soils should be based on crop N requirements and N mineralization considerations, and P mobility from biosolids of the type used should not pose a water quality risk. Four treatments were compared to address objective (iii): 426 Mg ha⁻¹ AD and 656 Mg ha⁻¹ LS biosolids; 0 (control) and 504 kg N ha⁻¹ y⁻¹ as conventional fertilizer. Contributions from CH₄ and CO₂ emissions to the radiative forcing were very small compared to N₂O. More N₂O was produced in the DRI biosolids treatments than in the conventional fertilizer treatments, and N₂O production was higher in AD than in LS. Expressed as global warming potentials, N₂O emissions from AD (101.5 Mg C ha⁻¹) were 4.6 times higher than from LS and 14.5-16.1 times higher than from the fertilizer treatments. High N₂O emissions from deep row incorporated biosolids reduce the C sequestration benefits of the DRI method. / Ph. D.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The growing demand for biofuels as alternative to petroleum-based fuels has instigated increased production of bioenergy crops. The southern half of Rio Grande do Sul, by having limited water resources for the production of soy, has received government incentives for the production of these crops, especially crops of sugar cane and cassava. However, there is need for more precise information regarding the proper management of these crops, and the influences of physical and hydraulic properties and mechanical soil on the growth and development of plants. Accordingly, this study aimed to determine the effect of different tillage systems on soil physical attributes, water and soil mechanics and its effects on the productivity of sugar cane and cassava. The study was conducted in the experimental area of the Soils Department, Federal University of Santa Maria in a Hapludalf. In two experiments were planted crops of sugar cane and cassava, in randomized blocks with three replications under different management systems and levels of compression: conventional tillage (CT) no tillage chiseled (NTC) no tillage (NT) and no tillage compacted (NTComp). Soil samples with preserved structure were collected for determination of physico-hydric soil density, pore size distribution curve of water retention, air and water flows, optimal water and compressive parameters: preconsolidation pressure (PP), compression index (CI) and elasticity of the soil. In addition, we calculated the indicators of soil quality: S ratio and relative density (RD) or degree of compression (GC). Soil preparation with mobilization (CT and NTC) alters the compacted soil, reducing soil bulk density and increased macroporosity and total porosity, but these effects are temporary and soil back to become thickened compromising the functionality of soil structure and plant development. A further compaction by traffic loader modifies the structure of Hapludalf, due to the increase in density and changes in distribution of soil pores, reducing macroporosity and total porosity, affecting the conductivity to water and air in the soil. The deeper layers were responsible for increased water storage in the soil. In the culture of cane sugar, NTC and NTComp retains higher water content, while the cassava crop, is the NT and NTC. Yield of both crops in association with the studied parameters, no-till soil management is offering the best physical condition and is indicated for production of sugar cane and cassava. / A crescente demanda de biocombustíveis como alternativa em substituição aos combustíveis derivados de petróleo tem instigado aumento da produção das culturas bioenergéticas. A metade sul do estado do Rio Grande do Sul, por apresentar limitações hídricas para a produção da soja, tem recebido incentivos governamentais para a produção dessas culturas, em especial às culturas da cana-de-açúcar e da mandioca. No entanto, há necessidade de informações mais precisas quanto ao manejo adequado a essas culturas, e as influências das propriedades físico-hídricas e mecânicas do solo sobre o crescimento e desenvolvimento das plantas. Nesse sentido, o presente estudo objetivou determinar o efeito de diferentes sistemas de preparo do solo nos seus atributos físicos, hídricos e mecânicos e na produtividade da cana-de-açúcar e da mandioca. O estudo foi realizado na área experimental do Departamento de Solos da Universidade Federal de Santa Maria em um Argissolo Vermelho-Amarelo Distrófico. Em dois experimentos foram plantadas as culturas da cana-de-açúcar e da mandioca, em delineamento de blocos ao acaso com três repetições, sob diferentes sistemas de manejo e níveis de compactação: plantio convencional (PC), escarificado (ESC), plantio direto (PD) e plantio direto compactado (PDC). Amostras de solo com estrutura preservada foram coletadas para determinação dos parâmetros físico-hídricos do solo: densidade, distribuição do tamanho de poros, curva de retenção de água, fluxos de ar e água, intervalo hídrico ótimo e os parâmetros compressivos: pressão de preconsolidação (σp), índice de compressão (IC) e elasticidade do solo. Além disso, foram calculados os indicadores de qualidade do solo: índice S e densidade relativa (DR) ou grau de compactação (GC). O preparo do solo com mobilização (PC e ESC) altera a camada compactada do solo, pela diminuição da sua densidade e aumentando a macroporosidade e a porosidade total, mas esses efeitos são temporários e o solo volta a se tornar adensado comprometendo a funcionalidade da estrutura do solo e o desenvolvimento das plantas. A compactação adicional pelo tráfego da carregadora modifica a estrutura do Argissolo Vermelho-Amarelo, em função do aumento da densidade e alterações na distribuição dos poros do solo, com redução da macroporosidade e porosidade total, comprometendo a condutividade à água e ao ar no solo. As camadas mais profundas foram responsáveis pelo maior armazenamento de água no solo. Na cultura da cana-de-açúcar, o PDC e o ESC retém maior conteúdo de água, enquanto na cultura da mandioca, é o PD e o ESC. Pelo rendimento de ambas as culturas em associação com os parâmetros estudados, o plantio direto é o manejo do solo que oferece as melhores condições físicas, sendo indicado para produção de cana-de-açúcar e mandioca.

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CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Empresa Brasileira de Pesquisa AgropecuÃria / Em regiÃes Ãridas e semiÃridas com campos de exploraÃÃo petrolÃfera, a Ãgua obtida junto com petrÃleo, conhecida como âÃgua produzidaâ (AP), vem sendo considerada para irrigaÃÃo. Devido a importÃncia dos microartrÃpodes para o funcionamento do solo, foram avaliadas as perturbaÃÃes promovidas pela AP sobre esses organismos. No capÃtulo I, foi avaliado se irrigaÃÃo com AP filtrada e AP tratada por osmose reversa, comparado com Ãgua do subsolo captada, altera a estrutura da assembleia de microartrÃpodes do solo em culturas de mamona e girassol em perÃodo seco e chuvoso. A abundÃncia e a riqueza de tÃxons de microartrÃpodes foram afetadas pela irrigaÃÃo e a sazonalidade na mamona. A estrutura da assembleia foi alterada durante a estaÃÃo chuvosa no girassol, e nas duas estaÃÃes na mamona. As perturbaÃÃes promovidas pela AP indicam que a mesofauna do solo pode ser utilizada no monitoramento ambiental da irrigaÃÃo. No capÃtulo II, foi avaliado o efeito da irrigaÃÃo com AP, da AP tratada por osmose reversa e do glutaraldeÃdo, utilizado no tratamento de osmose reversa, sobre os tÃxons da mesofauna na cultura de abacaxi ornamental. Avaliou-se, atravÃs de testes ecotoxicolÃgicos, a reproduÃÃo de Folsomia candida e Enchytraeus crypticus em solo coletado nos tratamentos apÃs um ano de irrigaÃÃo e em solo contaminado com glutaraldeÃdo. A AP influenciou Hymenoptera, Cosmochthonius sp, e Entomobryomorpha. A AP tratada por osmose reversa reduziu a reproduÃÃo de F. candida e E. crypticus e a AP filtrada afetou a reproduÃÃo de E. crypticus. O glutaraldeÃdo reduziu a reproduÃÃo de F. candida. Este estudo revela que a AP e o glutaraldeÃdo afetam os tÃxons da mesofauna reduzindo sua reproduÃÃo no solo. No capÃtulo III as respostas ambientais de Ãcaros Mesostigmata e do restante dos microartrÃpodes foram comparadas. MicroartrÃpodes foram coletados em parcelas irrigadas com as trÃs Ãguas e cultivadas com girassol e mamona e na vegetaÃÃo nativa durante a estaÃÃo seca e chuvosa. As respostas da abundÃncia e riqueza das duas assembleias em relaÃÃo a irrigaÃÃo e sazonalidade foram similares. Os Ãcaros foram afetados pela sazonalidade no girassol e pela irrigaÃÃo na mamona e o resto dos microartrÃpodes por ambos os fatores. Essas assembleias podem ser acessadas para monitorar sazonalidade uso do solo. / In arid and semiarid lands with continental oil fields, the water obtained with oil, known as "produced water" (PW), has been suggested as an alternative source for irrigation. Because the relevance of microarthropods assemblage for the soil, in this study was evaluated the disturbances promoted by the PW on those edaphic organisms. In Chapter I, was assessed whether the irrigation with PW filtered and PW filtered and then treated by reverse osmosis, comparing with groundwater from AÃu aquifer, changes the mesofauna in sunflower and castor bean crops during dry and rainy seasons. PW and seasonality changed the abundance and richness in castor bean. In the sunflower crop, the assemblage structure was different from the aquifer in PW treated by reverse osmosis during the rainy season, while in castor bean that difference occurred in both seasons. Disturbances promoted by PW on mesofauna can be used for environmental monitoring of irrigation. In Chapter II the effects of PW filtered, PW filtered and then treated by reverse osmosis and the glutaraldehyde, commonly used in treatment of PW by reverse osmosis, on microarthropods taxa was assessed in an ornamental pineapple crop. Ecotoxicological tests evaluated the survival and reproduction of Folsomia candida and Enchytraeus crypticus on soil samples collected in the treatments after a year of irrigation and in soil contaminated with glutaraldehyde. PW influenced Hymenoptera, Cosmochthonius sp. and Entomobryomorpha. The PW treated by reverse osmosis reduced reproduction of F. candida and E. crypticus and the PW filtered affected the reproduction of E. crypticus. Glutaraldehyde reduced the reproduction of F. candida. Our study reveals that AP and glutaraldehyde affect the mesofauna taxa reducing their reproduction. In chapter III the environmental responses of total microarthropod and Mesostigmata mites were compared. Microarthropods were assessed in irrigated plots under castor bean and sunflower cultivation, and native vegetation during the dry and rainy seasons. The response of the two assemblages to irrigation and seasonality was similar. Mites were affected by seasonality in the sunflower and by irrigation in castor bean crops, while the total microarthropod have been affected by both factors. Mesostigmata mites or total microarthropd assemblages can be assessed to monitor seasonality and land use.