Encouraging greater implementation of conservation agriculture practices such as reduced tillage and cover crops may require better understanding of the effect of these practices on soil health. The overall objective of this study was to quantify soil health dynamics due to conservation agriculture practices and address methodological gaps in terms of measuring soil health parameters. We developed five sites across the state of Virginia; each site had replicated plots with combinations of reduced tillage versus disk tillage and wintertime cover crops versus no cover crops as experimental treatments. Soil and plant samples were collected 1-2 times per year for 3 years, and were analyzed for 30 soil health parameters. The parameters were first evaluated to determine if any consistently detected treatment differences. We then quantified the temporal dynamics of the eight most responsive soil health parameters, while considering influences of soil water content at time of tillage, cover crop biomass, and previous land management history. Of the analyzed parameters, only 2-4 mm aggregate stability and magnesium showed high responsiveness and consistency in identifying tillage and cover crop effects. None of the parameters detected treatment differences in all sites or at all times, yet samples collected after high biomass cover crops or after tillage in wet conditions tended to show significant treatment differences for multiple indicators. The previous history of management in each site may have affected trends in aggregate stability, but did not appear to influence other indicators. As soil aggregate stability was found to be the most important soil health parameter, our third study developed an improved method for measuring soil aggregate stability. This new method, Integrated Aggregate Stability (IAS), interprets aggregate stability using a laser diffraction machine. Overall, IAS showed higher correlation with the wet sieving method (R2 = 0.49 to 0.59) than widely used median aggregate size (d50) (R2 = 0.09 to 0.27). IAS can also quantify stability of macro- and micro-sized aggregates, which d50 cannot. When comparing between IAS and wet sieving, IAS requires considerably less time and sample amounts. Our fourth study focused on creating an inexpensive yet accurate tool for measuring soil respiration, as microbial assessments based on respiration rates have great potential for detecting rapid changes in soil health. Using an Arduino-based infrared gas analyzer (IRGA) sensor, we developed the Soil Microbial Activity Assessment Contraption (SMAAC) for less than $150. Our results show that SMAAC provided consistent readings with a commercial IRGA unit when tested using three different configurations. Altogether, the research presented in this dissertation identifies important soil health parameters and quantifies their temporal and between-site dynamics. Using this narrower set of indicators can help producers and practitioners save resources when conducting measurements to assess soil health effects of agricultural practices. Further, this work also provides improved measurement techniques for useful soil health parameters like aggregate stability and soil respiration. These findings and innovations should help to encourage greater adoption of agricultural management practices that build and preserve soil health. / Doctor of Philosophy / If we want to make sure that ample and safe food is available to future generations, then it is time that we produce food without damaging the soil. Many widely used soil management techniques like tillage and leaving the field bare can harm the soil and decrease productivity in the long run. One potential technique to produce food while protecting the soil and environment is conservation agriculture, which can include reduced tillage and cover cropping. Reduced tillage is a technique in which we grow food without majorly disturbing the soil, while cover crops are planted when cash crops are not in the field in order to improve or sustain the soil. Understanding the soil-related benefits of conservation agriculture practices is important to encourage farmers to adopt these practices. In this study we tested the effects on soils of reduced tillage and cover crop practices versus conventional tillage and bare soil practices, using five locations across Virginia. We also developed improved methods for measuring two informative soil parameters. We found that, when looking at all of our five sites, the stability of soil aggregates, the rate at which water enters soil, and the nutrients in surface soils were all affected by the type of management that the soils were subjected to. Reduced tillage increased stability of soil aggregates when compared with conventional till. This increased stability of aggregates indicators lower potential for surface water runoff, erosion, and flooding when we practice reduced tillage. Cover cropping also increased stability of soil aggregates, especially when the cover crops attained substantial above-ground mass. Soil nutrients (which are essential for plants to grow) were also overall higher in the surface soil layers under no-till. Since the stability of soil aggregates was found to be an important benefit of CA practices, we also perceived a need for a better method for measuring stability of these aggregates. In response, we developed a new index called Integrated Aggregate Stability (IAS). IAS was found to give similar results as established methods, but the time required to get IAS result is about 10 minutes, whereas the time required for established methods like wet sieving is around 2 days. IAS measurements are therefore both accurate and quick to perform. We also focused on developing an inexpensive tool for measuring soil respiration. Soil respiration-based measurements help us to understand the activity of microbes in the soil. These microbes are very important for soils to function. Our tool, Soil Microbial Activity Assessment Contraption (SMAAC), was very consistent with a currently used tool and shows high potential for future use. Altogether, we found that no-tillage and cover cropping can increase stability of soil aggregates even within 1-3 years of starting those practices. No-till can also increase nutrient concentrations in the top soil layer. The tools and innovations developed in this study have the potential to increase the ability of farmers to assess soil health and also encourage greater adoption of conservation agriculture practices.

Made available in DSpace on 2016-04-26T19:39:29Z (GMT). No. of bitstreams: 1 2006-Luciano Lopes Reis.pdf: 1765828 bytes, checksum: e031c34734485e7d84bd20e5fcc0d59b (MD5) Previous issue date: 2006-02-24 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / This study had as objective to monitor the process of environmental reclamation of tanks filled with residues from bauxite washings, vegetated by hydro-sowing legume trees species inoculated with rhizobia, and asbuscular mycorrhizal fungi. Nutrient fertilizers, without nitrogen, were added at the mixture at sowing. Later it was planted a mixture of native tree species seedlings, with a high proportion of N2-fixing legumes, in an experiment with additional increasing levels of fertilizers and liming, except for nitrogen. The deposits of sterile bauxite subsoil, vegetated with the mix of native species, with high proportion of legumes capable of N2 fixation and mineral fertilization, were evaluated at different periods of time, for the chemical and biological attributes of soil and plants. Samples of soil, leaves, litter, and soil invertebrates fauna were taken in 2002, 2003 and 2004, to measure nutrient availability in soil; foliar nutrient level of indicator plants; soil microbial biomass and activity; soil fauna activity, diversity and ecological indexes; and evaluation of vegetal coverage of the SP1 residue tank. The results of foliar analyses indicated that even at the highest level of fertilizer and lime additions in the SP1 residue tank were not sufficient to meet the adequate plant nutrition requirements, indicating the need of higher input of nutrients. By using multivariate statistical analyses of the data, it was possible to distribute the studied systems along Cartesian axis, where the native forest area, used as testimony, and old vegetated mining sites (planted in 1984, 1992 and 1994) were clustered together; while the most recent vegetated mining sites and the tanks filled with residues formed a distant cluster. Among the index attributes studied Al+3, total C, total N, K, soil pH, microbial carbon and respiration; and Ca and Mg from litter were the principal factors determining the ordering and distinction between reclamation sites. The reclamation methodology used in the residue tank SP1, which combined the hydro-sowing with application of low solubility fertilizers, using a mix of seeds from medium cycle legume trees inoculated and with mycorrhizae, with later planting of native seedlings and manual dispersion of seeds, showed to be an important technique to stimulate natural vegetation growth. Also, the technique resulted in a high capacity of addition of decidual material, and the legume tree Acacia holosericea showed the best capacity for soil coverage and input of nutrients. / Com o objetivo de monitorar o processo de recupera??o ambiental de tanques de dep?sito de rejeito da lavagem da bauxita, revegetados atrav?s da hidrossemeadura de leguminosas fixadoras de N2 e com adi??o de fungos micorrizicos, mais aporte de nutrientes. Posteriormente, foi feito o plantio de mudas nativas em experimento de n?veis de aduba??o e calagem, sem aplica??o de nitrog?nio. Os dep?sitos de subsolo est?ril em bauxita revegetados com mistura de esp?cies nativas, com grande propor??o de leguminosas fixadoras de N2 e aduba??o mineral na cova, avaliados em diferentes idades, foram utilizados atributos qu?micos e biol?gicos do solo e planta. Foram realizadas coletas de solo, de folhas, de serapilheira e da fauna de invertebrados do solo, nos anos de 2002, 2003 e 2004, para determina??o da disponibilidade de nutrientes no solo; dos teores foliares de nutrientes das plantas indicadoras; da biomassa e atividade microbiana; da atividade, diversidade de grupos e ?ndices ecol?gicos da comunidade da fauna do solo; e avalia??o da cobertura vegetal do tanque de rejeito SP1. Os resultados da an?lise foliar das esp?cies indicadoras e de disponibilidade de nutrientes no solo indicaram que nem os maiores n?veis de aduba??o e calagem utilizados no experimento do tanque de rejeito SP1 foram suficientes para permitir uma adequada nutri??o ?s plantas, indicando a necessidade de novos aportes de nutrientes. Atrav?s da aplica??o de ferramentas de estat?stica multivariada aos dados, foi poss?vel ordenar os sistemas estudados ao longo de eixos cartesianos, onde a ?rea de mata nativa, usada como testemunha, e reflorestamentos sobre res?duos de minera??o com maior idade (realizados nos anos de 1984, 1992 e 1994) se ordenam pr?ximos uns dos outros, enquanto que os reflorestamentos sobre est?ril mais recentes e ?reas dos tanques de rejeito se ordenam distantes destes, formando grupamentos entre si. Dentre os atributos indicadores utilizados, o Al+3, C total, N total, K e pH do solo; a respira??o e carbono microbiano; e o Ca e Mg da serapilheira foram os mais determinantes para o ordenamento e distin??o entre os sistemas em recupera??o. A metodologia de recupera??o utilizada no tanque de rejeito SP1 que combinou a pr?tica da hidrossemeadura com aplica??o de formas de adubos pouco sol?veis, utiliza??o de coquetel de sementes de leguminosas arb?reas de ciclo m?dio inoculadas e micorrizadas, posterior plantio de mudas nativas e lan?amento manual de sementes, mostrou-se como importante t?cnica propulsora da regenera??o natural. A t?cnica tamb?m resultou em elevada capacidade de aporte de material decidual, sendo a leguminosa arb?rea Acacia holosericea, a esp?cie que apresentou melhor capacidade de cobertura do solo e aporte de nutrientes.

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Soil health-based agricultural management practices are widely promoted to improve soil structure, infiltration and reduce erosion. This study was conducted at two locations in North-Central Mississippi to evaluate the influence of different cover crop species and poultry litter on soil health that can impact crop production, climate change, and resilience. The results indicated that the cover crops showed a little effect on some soil health indicators compared to control treatment. However, in one location, rye, and a mixture of cover crops decreased bulk density and increased available water content and organic matter. The poultry litter had a positive effect on most soil physical and chemical health indicators. The cover crop species at Pontotoc decreased bulk density, increased field capacity, CEC, and total carbon. However, there was no significant effect of cover crops on most soil chemical health indicators, and soil responses may take more than five years for the changes to appear.