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Climate change and soil fertility decline are major threats to smallholder farmers' food and nutrition security in southern Africa, and cropping systems that improve soil health are needed to address these challenges. Cropping systems that invest in soil organic matter, such as no-tillage (NT) with crop residue retention, have been proposed as potential solutions. However, a key challenge for assessing the sustainability of NT systems is that soil carbon (C) stocks develop over long timescales, and there is an urgent need to identify trajectory indicators of sustainability and crop productivity. Here we examined the effects of NT as compared with conventional tillage without residue retention on relationships between soil characteristics and maize (Zea mays L.) productivity in long-term on-farm and on-station trials in Zimbabwe. Our results show that relationships between soil characteristics and maize productivity, and the effects of management on these relationships, varied with soil type. Total soil nitrogen (N) and C were strong predictors of maize grain yield and above-ground biomass (i.e., stover) in the clayey soils, but not in the sandy soils, under both managements. This highlights context-specific benefits of management that fosters the accumulation of soil C and N stocks. Despite a strong effect of NT management on soil C and N in sandy soils, this accrual was not sufficient to support increased crop productivity in these soils. We suggest that sandy soils should be the priority target of NT with organic resource inputs interventions in southern Africa, as mineral fertilizer inputs alone will not halt the soil fertility decline. This will require a holistic management approach and input of C in various forms (e.g., biomass from cover crops and tree components, crop residues, in combination with mineral fertilizers). Clayey soils on the other hand have greater buffering capacity against detrimental effects of soil tillage and low C input.

The study of interrelationships among soil health indicators is important for (i) achieving better understanding of nutrient cycling, (ii) making soil health assessment cost-effective by eliminating redundant indicators, and (iii) improving nitrogen (N) fertilizer recommendation models. The objectives of this study were to (i) decipher complex interrelationships of selected chemical, physical, and biological soil health indicators in pastures with history of inorganic or broiler litter fertilization, and (ii) establish associations among inorganic N, potentially mineralizable N (PMN), and soil microbial biomass (SMBC), and other soil health indicators. In situ soil respiration was measured and soil samples were collected from six beef farms in 2017 and 2018 to measure selected soil health indicators. We were able to establish associations between easy-to-measure active carbon (POXC) vs. PMN (R2 = 0.52), and N (R2 = 0.43). POXC had a noteworthy quadratic relationship with N and nitrate, where we found dramatic increase of N and nitrate beyond an inflection point of 500 mg kg−1 POXC. This point may serve as threshold for soil health assessment. The relationships of loss-on-ignition (LOI) carbon with other soil health indicators were discernable between inorganic- and broiler litter-fertilized pastures. We were able to establish association of SMBC with other soil variables (R2 = 0.76) and there was detectable difference in SMBC between inorganic-fertilized and broiler litter-fertilized pastures. These results could be useful for cost-effective soil health assessment and optimization of N fertilizer recommendation models to improve N use efficiency and grazing system sustainability.

International audience; An experiment has been designed in the Highlands of Madagascar withthe aim to produce multi-criteria indicators of performance ofagroecological practices. In this experiment, different traditionaland innovative practices were tested in field conditions with theassumption that practices that enhance soil biodiversity and soilecological processes are the one that best promote plant production,yield and sustainability. Both ecological and agronomic performanceswere confronted with socio-economic performance defined by farmers inorder to propose innovative practices adoptable by farmers.A 2-year field experiment with 16 different practices, replicated 4times, was designed in the Highlands of Madagascar with upland riceas the main crop. Many soil and plant parameters were measured: 73parameters to describe soil biodiversity and soil ecologicalprocesses, 19 descriptors to measure rice production, nutrition andyield, and 8 socio-economic descriptors.This study led to the production of a useful indicator allowing toevaluate an agroecological practice on the way it promotes soil healthand especially soil biodiversity, crop yield and socio-economicalrequirements which are the main limits for practice adoption. Wemeasured interesting relations between soil ecological descriptorsand agronomic descriptors.

The use of permanganate oxidizable carbon (POXC) as a soil health indicator has gained traction due to its low analysis cost and potential for high-throughput analysis. Permanganate (MnO4−) has long been proposed to fractionate soil organic matter. A methodological alteration was proposed to allow for its use as a rapid soil health indicator (POXC) is to allow the MnO4− to reach with a fixed soil mass, rather than a fixed mass of soil organic carbon (SOC). However, this modification may compromise the robustness of the results by altering the consistency of the stoichiometry in the reduction–oxidation reaction (MnO4− : SOC). Here we use a diverse set of 69 U.S. soils to evaluate whether using a fixed soil mass (2.5 g) substantively undermines the theoretical requirement of a fixed amount of SOC (15 or 25 mg SOC per sample) per unit of oxidant (MnO4−). We found that the use of a fixed SOC mass entailed a more consistent reduction of MnO4− than a fixed soil mass and also resulted in a greater range of absolute (mg kg−1) and relative POXC values (as a % of SOC) across soils. This broader range of values was not driven by large differences in the amount of MnO4− reduced per unit of SOC analyzed, but rather resulted from normalizing the amount of MnO4− reduced on a soil mass basis. The underlying distribution of MnO4− reduction did not substantively change, suggesting that the interpretation when comparing relative differences in POXC would similarly be unchanged. Unexpectedly, the use of a fixed SOC mass decreased the repeatability of the metric relative to the use of a fixed soil mass. Given the current interpretation of POXC, we see few upsides of using fixed SOC mass and several downsides (i.e. lower throughput and decreased reliability), relative to the current use of a fixed soil mass. To minimize unfounded assumptions, we further propose that POXC values be reported strictly as MnO4− reduced, specifically as μmol MnO4− reduced kg−1 soil. Our results further underscore that the results of POXC assays should be cautiously interpreted. Specifically, interpretations should be qualified by the operationally-defined nature of the POXC assay as an indirectly measured, chemically defined fraction.

Modern agriculture fundamentally relies on an extensive use of agrochemicals to enhance crop productivity by controlling harmful pests, pathogens, and undesirable weeds. However, currently, we have reached a stage where several threats are emerging on food security, human and environmental health, maintenance of ecological balance, and conservation of the soil biodiversity. Long-term unbalanced use of agrochemicals may lead to community shift of beneficial microorganisms with dangerous consequences such as the development of antimicrobial resistance. Agrochemicals usage in farming systems may adversely influence soil microorganisms that are mainly involved in nutrient cycling processes, such as nitrogen fixation, phosphorus solubilization, and other essential nutrient biotransformation. The recent report established that some agrochemicals reduce biochemical reaction and activities of soil enzymes that are key indicators of soil microbiological health. This chapter focuses on the effects of applied agropesticides on soil microbiological and biochemical health attributes under different cropping systems.

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.

El carbono orgánico (CO) y el nitrógeno (N) incubado en anaerobiosis (Nan) son indicadores de calidad del suelo. Además, el Nan es un estimador del aporte de N por mineralización, y ha sido empleado para el ajuste de la dosis de N en los cultivos. Los objetivos de este trabajo fueron: 1) relevar y mapear los contenidos de CO total (COT) y de Nan en suelos agrícolas de la provincia de Buenos Aires y 2) relacionar dichas variables a escala regional. Se emplearon un total de 31.776 y 6556 muestras de suelo tomadas a 0-20 cm de profundidad para COT y Nan, respectivamente. La eficiencia de predicción fue 79% para COT y 67% para Nan. El contenido de COT varió entre 3,5 y 80,8 g kg-1, aumentando de noroeste a sureste de la provincia de Buenos Aires. La concentración de Nan varió entre 12 y 260 mg kg-1, siendo mayores los contenidos en el este que en el oeste. Esto evidencia el diferente potencial aporte de N por mineralización que poseen los suelos, el cual debería ser considerado al momento de ajustar la dosis de N para los cultivos. Se encontró una asociación significativa entre los contenidos de COT y Nan a nivel regional (R2 = 50%). No obstante, la estimación del contenido de Nan de los suelos a partir del COT no sería una práctica recomendable a los fines del diagnóstico de N a escala de lote. Sin embargo, los mapas y la relación obtenidos podrían ser utilizados en una primera instancia para el diagnóstico de la fertilidad a escala regional y como orientativos a escala de lote. Fil: Reussi Calvo, Nahuel Ignacio. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Fertilab; Argentina Fil: Studdert, Guillermo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce; Argentina Fil: Calandroni, Mirta Beatriz. Fertilab; Argentina Fil: Diovisalvi, Natalia Verónica. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina Fil: Cabria, Fabián Néstor. Fertilab; Argentina Fil: Berardo, Angel. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina

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.

PhD (Agriculture with Agronomy), North-West University, Mafikeng Campus Grape growing and winemaking process generate enormous amounts of solid waste materials that demand more economical and safe disposal technologies. In this study, co-composting and effective microorganisms (EM) technologies were employed to treat the winery solid waste (WSW), thereafter, the resultant compost was assessed for its physico-chemical properties, phyto-toxicity, nutrient release patterns and agronomic potential. Four WSW compost types produced comprised of EM inoculated or uninoculated compost with an initial heap height (hereinafter pile size) of 1.0 or 1.5 m. Samples of the cured composts were evaluated for physico-chemical properties and germination attributes at different extract concentrations (0, 10, 25, 50 and 100%) using cowpea, maize and tomato seeds. The results demonstrated that EM inoculation exerted a significant effect on compost Bray-2 P content while the interaction of EM inoculation and pile size similarly had significant effects on the ammonium-N content. The produced composts possessed high electrical conductivity values due to high concentrations of soluble salts that could be potentially toxic to crops and soil. The use of 1.0 m pile size promoted extended thermophilic phase during compost production that could ensure better sanitization of the final product. Maize and tomato showed higher degrees of phyto-toxicity at 50% extract concentration and above. The phyto-toxicity effects recorded in maize and tomato may be minimized by using lower application rates. The incubation study was carried-out using a buried-bag procedure to determine the P and K release patterns of inoculated compost with 1.0 m pile size in sandy loam soil under field conditions. Grounded compost was thoroughly mixed in zip-lock bags with 900 g surface soil at rates equivalent to 0, 5, 10, 20 and 40 t ha-1. One bag per treatment was destructively sampled at 0, 7, 21, 42, 63, 84, 105 and 126 days of incubation during which the available P and exchangeable K were analyzed. Net mineralized P ranged from -62 to 86 mg kg-1, while the net mineralized K varied between 41 and 2047 mg kg-1. The high net P and K mineralization suggests that the WSW compost can be used as a P and K source. However, its utilization as soil amendment must be cautious to mitigate the potential risks of unnecessary soil pH increase, nutrient imbalance, toxicity and the antagonistic effects of P and K on other plants nutrients. The study was conducted under tunnel house conditions to determine the optimum application rates and agronomic potentials of the WSW compost. The treatment factors comprised of four WSW compost types, seven compost rates (0, 5, 10, 20, 40, 80 and 100 t ha-1) and two sandy loam soils. The results showed a general increase in stem girth, plant height, number of functional leaves per plant, dry matter yield and relative agronomic effectiveness with increasing compost rate. The microbial inoculation and variation of compost with pile size did not induce significant effects on maize performance and soil chemical properties. In most cases, the higher optimum rates predicted by the quadratic model were associated with dry matter yield that were slightly higher in comparison to the optimum dry matter yield predicted by the linear-plus-plateau model. The 80 t ha-1 rates and above significantly increased the exchangeable soil-Na content by up to 175%, thereby causing harm to maize seedlings. Although the WSW compost has an immense potential for the improvement of maize productivity, its application at rates above 40 t ha-1 is detrimental to both plants and the soil. Field trials were conducted during the 2018 and 2018/19 summer cropping seasons to evaluate the effects of sole and combined application of inorganic N and P fertilizers (INPF) and WSW compost on maize performance and soil chemical properties. Inoculated and uninoculated compost types with pile size of 1.0 m were used. The INPF and each compost type were combined in different ratios (0:0, 75:25, 50:50, 25:75 and 0:100, w/w) in such a way that the total mineral N and P supplies from both sources were equivalent to that supplied by the established optimum rate of WSW compost under the tunnel house conditions. The recommended rates of inorganic fertilizers of 200 kg N ha-1 and 90 kg P ha-1 were mixed and included as a standard control. Treatments were arranged in factorial arrangement fitted in a RCBD with three replicates. The results showed a significant interaction effect of compost type and application rate on plant height and leaf area index during the 2018 season, and on number of leaves and stem girth at tasselling during the 2018/19 season. The grain yields recorded from the 25:75 and 50:50 compost-INPF combinations were 6649 and 6246 kg ha-1 respectively and were significantly higher than 4557 kg ha-1 for the untreated control under the harsh environmental conditions of the 2018/19 season. Compost application alone or combined with INPF increased soil pH and the contents of soil organic C, P, K, Na and Zn. Doctoral

Most soil studies aim a better characterization of the system through indicators. In the present study nematofauna and soil structure were chosen as indicators to be assess soil health as related to agricultural practices. The field research was carried out on the two fodder cropping systems continuous maize (CM, Zea mays L.) and a 3-year rotation of silage-maize – silage-barley (Hordeum vulgare L.) with Italian ryegrass (R3) and grain-maize maintained in these conditions for 18 years. Each crop system was submitted to two management options: 1) the high input level (H), done as a conventional tillage, 2) the low input level (L), where the tillage was replaced by harrowing and the manure was reduced by 30%. The effects of the two different cropping systems was assessed on soil nematofauna and soil physic parameters (structure or aggregate stability). Comparison was made of general composition, trophic structure and biodiversity of the nematofauna collected in both systems. Differences in nematode genera composition and distribution between the two systems were also recorded. The monoculture, compared to the three year rotation, had a negative influence on the nematofauna composition and its ecological succession. The Structural Stability Index (SSI) values indicate that both the cropping systems had a negative effect on the aggregate stability. The results indicate that nematofauna can be used to assess the effects of cropping systems on soil ecosystem, and therefore be considered a good indicator of soil health to integrate information from different chemical or physical indicators.