The application of municipal sewage biosolids to agricultural land is a common practice worldwide. Increasing attention is being directed at the presence of organic contaminants bound to the organic phase during wastewater treatment, which end up in the biosolids. The goal of this study was to investigate the decomposition of an alkaline-stabilized biosolid being used as an agricultural soil amendment containing unknown organic contaminants. A two year field trial and a 120 day laboratory soil incubation using increasing rates (0, 7, 14, 28, and 42 Mg ha-1) of an alkaline-stabilized biosolid (ASB) were set up to monitor biosolid decomposition and concentrations of selected contaminants over time. The seven contaminants selected for monitoring (p-cresol, indole, 4-t-octylphenol, phenanthrene, triclosan, carbamazepine, and benzo[a]pyrene) represent a wide range of physico-chemical properties and fall under several different chemical classes. The decomposition of ASB in soil was examined in the incubation study. Almost half of the CO2-C evolved from ASB amended soils occurred within the first 6 days, indicating that a relatively labile pool of carbon remains in ASB following the sewage treatment process. By day 121, between 71 to 78% of the total carbon added to soil had been evolved as CO2-C. A new model developed during this study to describe carbon mineralization, a first order plus logistic function (FLOG), performed better than other commonly used models. The method chosen to analyze organic contaminants in soil was only able to determine four out of seven compounds reliably, with recoveries greater than 50% for 4-t-octylphenol, phenanthrene, triclosan, and benzo[a]pyrene. In treated soils, only triclosan was able to be detected and quantified. Average triclosan concentration in the incubation study ranged from a high of 143 ng g-1 on day 3 to a low of 26 ng g-1 by day 121, representing an 81% decrease over a roughly 4 month period under idealized conditions. In the field, triclosan concentrations following a Fall biosolids application in Oct. 2008 increased to detectable levels (29 to 47 ng g-1) in all three plots measured in Nov. 2008, which remained elevated (29 to 66 ng g-1) over the winter period in two out of three plots when sampled in May 2009. Following the Spring application in June 2009, measured triclosan concentrations in July 2009 samples from these same two plots were lower than predicted (33 to 48 ng g-1) and eventually decreased to levels below the detection limit by the Oct. 2009 sampling.

The combined effect of temperature, moisture and phosphorus availability on soil organic matter mineralization in permafrost affected soils of northern circumpolar region was investigated. This study was a part of research activities of the European project CryoCARB and it was primarily focused on the cryoturbated organic horizons of permafrost affected soils. During this study, the temperature sensitivity of the organic matter mineralization and its relation to the soil moisture and phosphorus availability was investigated using series of incubation experiments and field measurements.

Animal manures are land applied in agronomic systems to supply essential crop nutrients and decrease dependency on chemical fertilizers. Liquid manures are traditionally surface broadcast to fields and sometimes incorporated to reduce odor and nutrient losses; however, incorporation is incompatible with no-till agriculture. Subsurface manure injection is a no-till compatible alternative application method which addresses these concerns, but likely changes the dynamics of nutrient cycling. Comparison of the two application methods has yielded mixed results and warrants further research. Therefore, the objectives of this research were to contrast the surface broadcast and subsurface injection of dairy slurry on nitrogen and carbon cycling, crop yield, and biologic responses to proxy soil health. In a forced air-flow laboratory incubation, manure injection reduced ammonia volatilization by 87% and 98% in a sandy loam and clay loam soil, respectively. The increased ammoniacal nitrogen recovery resulted in increases of soil nitrate of 13% for the sandy loam and 26% for the clay loam after 40 days of incubation. Microbial measurements were inconclusive in the laboratory. In 7 site-years of field study, soil nitrate was greater in 7 of 25 measurements under manure injection and 30% higher under injection on average during the corn pre side-dress nitrate test (PSNT) time. Soil nitrate sampling methods were assessed for fields injected with manure; a standard random sampling method had a coefficient of variation (C.V.) of 28% and was as equally repeatable as utilizing an equi-spaced distribution of cores taken across an injection band, C.V. of 30%. Both biological responses, carbon mineralization (C-min) and substrate induced respiration (SIR), were not different between application methods; both were highly variable and C-min was especially intensive logistically. Corn yield showed no consistent response to application method, but probably was not nitrogen limited. In 2 years of field study conducted on a university research farm injection resulted in greater 0-15cm soil nitrate levels than surface broadcast 1 week after application and persisted for 9 additional weeks. In injected plots, nitrate was concentrated in the injection band; nitrate movement was significant only 10cm lateral to the injection band but overall distribution fit well to a second degree polynomial, especially 2 and 4 weeks after application, R2>0.80. Evidence of leaching was observed in one year after receiving considerable rainfall in weeks 1 and 2 after application. When corn grain yield was averaged year over year, injection was 26% greater than the no- manure control, and 15% greater than surface application. Both biological metrics, C-min and microbial biomass, were stratified by depth; C-min was concentrated within the manure band leading to greater mineralization under injected applications. Microbial biomass was significantly higher under injection at the 15-30cm depth. Overall biological response to manure application method was inconclusive, however manure injection is superior to surface application in terms of nitrogen recovery. / Doctor of Philosophy / Animal manures supply nutrients essential to crop growth (notably nitrogen and phosphorous); liquid manures (pigs and dairy cattle) are commonly applied by spraying them on soils before tillage. Where no-tillage is used as a conservation measure subsurface injection can be used as an alternative to leaving manure on the soil surface. The purpose of this research was to assess nutrient cycling, crop yield, and soil health impacts of surface applied and injected dairy manure applications. Manure injection greatly reduces a nitrogen loss pathway, and as a result supplies more plant available nitrogen to the crop. Methods of soil sampling fields using injection were compared and a recommended sampling method was defined. Transport of a form of nitrogen vulnerable to movement in the ground was found to only travel 10cm away from where manure was injected. Transport of this form of nitrogen below the injection area was observed after abundant rainfall. Crop yields were sometimes higher under injection however, yields are also determined by factors other than nitrogen. Soil health was not repeatably improved under one application method, but microbial activity was greater at shallower soil depths.

Saltwater intrusion due to global change is expected to have a detrimental effect on the biogeochemistry of tidal freshwater wetlands. Of particular concern is that fact that salinization can alter the role of these ecosystems in the global carbon cycling by causing shifts in microbial metabolism that alter greenhouse gas emissions and increase carbon mineralization rates. However, our understanding of how wetland microbial community dynamics will respond to saltwater intrusion is limited. To address this knowledge gap and increase our understanding of how microbial communities in tidal freshwater wetlands change over time (1, 3, 12, and 49 weeks) under elevated salinity conditions, an in situ soil transplant was conducted. Throughout the 49 weeks of saltwater exposure, salinity had no effect on soil quality (organic matter content and C:N ratio). In contrast, the concentration of porewater ion species (SO4-2, NO3-, and NH4+) considerably increased. The activity of hydrolytic enzymes, (ß-1,4-glucosidase and 1,4-ß-cellobiohydrolase) gradually decreased with prolonged exposure to saline conditions; by the final sampling event (49 weeks), activity was reduced by ~70% in comparison to the freshwater controls. Short term exposure to salinity (3 and 12 weeks) had a greater effect on phenol oxidase, decreasing activity by 10-20%. Saltwater exposure had an immediate (1 week) effect on potential rates of carbon mineralization; overall, carbon dioxide production doubled and methane production decreased by ~20-fold. These changes in gas production were correlated to increased salinity and to changes in the abundance of methanogens and sulfate reducing bacteria, suggesting a shift in the terminal step in organic matter degradation from methanogenesis to sulfate reduction. Principal component analysis revealed distinct changes in soil environmental conditions and carbon metabolism within weeks, but the response of the microbial community was slower (months to a year). Taken together, results from this study indicate that the response of tidal freshwater wetlands to salinization is driven by complex interactions of microbial related processes and environmental changes that are dependent on the duration of exposure. Assessing the impact of environmental perturbation on ecosystem function may be better achieved by complementary analysis of both microbial community structure and function.

Doctor of Philosophy / Department of Agronomy / Charles W. Rice / Increasing atmospheric CO2 concentrations and other greenhouse gases have been linked to global climate change. Soil organic C (SOC) sequestration in both agricultural and native ecosystems is a plausible option to mitigate increasing atmospheric CO2 in the short term. Laboratory and field studies were conducted to (1) understand the influence of soil water content on the temperature response of SOC mineralization (2) investigate burn and nutrient amendment effects on biogeochemical properties of tallgrass prairie and (3) assess perennial and annual plant management practices on biophysical controls on SOC dynamics. The laboratory study was conducted using soils collected from an agricultural field, currently planted to corn (C4 crop), but previously planted to small grain (C3) crops. The changes in cultivated crops resulted in a δ¹³C isotopic signature that was useful in distinguishing older from younger soil derived CO2-C during SOC mineralization. Soils were incubated at 15, 25 and 35 oC, under soil water potentials of -1, -0.03 and -0.01 MPa. Soil water content influenced the effect of temperature on SOC mineralization. The impact of soil water on temperature effect on SOC mineralization was greater under wetter soil conditions. Both young and older SOC were temperature sensitive, but SOC loss depended on the magnitude of temperature change, soil water content and experiment duration. Microbial biomass was reduced with increasing soil water content. The first field experiment investigated burn and nutrient amendment effects on soil OC in a tallgrass prairie ecosystem. The main plots were burned (B) and unburned (UB) tallgrass prairie and split plots were nutrient amendments (N, P or N+P including controls). Vegetation was significantly altered by burning and nutrient amendment. Treatment effects on either TN or SOC were depth-specific with no impact at the cumulative 0-30 cm depth. The P amendment increased microbial biomass at 0-5 cm which was higher in unburned than burned. However, at 5-15 cm depth N amendment increased microbial biomass which was higher in burned than unburned. In conclusion, soil OC in both burned and unburned tallgrass prairie may have a similar trajectory however; the belowground dynamics of the burned and unburned tallgrass prairie are apparently different. Another field experiment assessed SOC dynamics under perennial and annual plant management practices. The main plots were grain sorghum (Sorghum bicolor) planted in no-tillage (NT) or continuous tillage (CT), and replanted native prairie grass, (Andropogon gerardii) (RP). The spit plots were phosphorus (+P) and control without P (-P). The P amendment was used to repress arbuscular mycorrhizal fungi (AMF), known to influence soil aggregation. The macroaggregate >250 µm, SOC and TN were higher in RP and NT than CT. The relative abundances of AMF and saprophytic fungi were greater with less soil disturbance in RP and NT than in CT. Therefore, less soil disturbance in RP and NT increased AMF and fungal biomasses. The higher relative abundances of AMF and fungi with less soil disturbance increased macroaggregate formation in RP and NT, which resulted in higher SOC sequestration in RP and NT than CT.

In Limpopo Province of South Africa, poor soil fertility and low crop yields are serious problems facing resource poor smallholder farmers. A survey of over 60 farmers in 2 villages (Gabaza and GaKgoroshi) found that most of the smallholder farmers were women (68%), elderly (50% above 68 years of age) and had not attended school or only attended up to the primary level (80%). Very few farmers kept livestock (usually in small numbers) and most grew cereal and legume crops (on 1ha of land) for home consumption and livestock feed, with legumes being planted on 13% of the land. The study showed that 80% of farmers were not fully aware of the benefits of legumes in fixing nitrogen (N) and improving yield. A field study at the survey village of Gabaza found that the application of fertiliser N and grass mulch combination and fertiliser N plus guarbean mulch significantly increased plant height and maize shoot growth at 4 and 8 weeks after planting. However, when grass mulch was without N fertiliser, there was no increase in maize growth relative to the control (0N). A farming systems simulation model (Agricultural Production Systems sIMulator - APSIM) was used to simulate this field study as well as over the long-term (1971 to 2008). Simulation analysis showed poor average maize yield (<3000 kg ha⁻ ¹) with the application of grass residues even when used with 30 kg N fertiliser. However, the application of guarbean residues as mulch with or without N fertiliser and as green manure increased maize yields to >4000 kg ha⁻ ¹. Simulation showed that the grass mulch with or without the addition of N fertiliser reduced water stress and soil water evaporation but increased N stress during the reproductive phase of the crop in most seasons. When guarbean mulch was used as green manure by itself, or mulch plus N fertiliser, N stress was reduced but water stress and soil water evaporation were increased which could have been due to faster decomposition of legume mulch as compared to grass mulch. Addition of N fertiliser reduced N stress to maize but increased water stress and soil water evaporation similar to the guarbean mulch because of high soil evaporation. APSIM analysis clearly showed the importance of N x soil water interactions in determining maize growth and yield at Gabaza. Therefore, two studies were undertaken in the laboratory in Australia to determine the dynamics of carbon (C) and N where residues of different qualities [canola (C:N 43), wheat (26), pea (9) and mucuna (14)] were applied to clay loam (Tarlee) or sandy (Waikerie) soils. In experiment 1, where residues were incorporated into the two soils, the cumulative CO₂-C evolution for the wheat and canola treatments at the end of the incubation period were fairly similar but significantly higher than for pea, mucuna and the control. In general, the application of residues increased microbial biomass C more than the control, with highest increases up to 1.48 and 1.56 mg C g⁻ ¹ soil for canola and wheat in Tarlee soil, respectively and 0.82 mg C g⁻ ¹ soil for pea in Waikerie soil. Even though the Tarlee soil showed greater C release than Waikerie soil, the C turnover from the residues between the 2 soils was not significantly different except for pea residues. Canola and wheat residues were found to immobilise N whereas N content increased in both soils with the application of legumes (pea and mucuna). In experiment 2, mucuna, pea and wheat residues were either incorporated or applied as surface mulches on Waikerie soil. Initially the CO₂-C release was higher for incorporated than mulched residues and CO₂-C released was higher for pea residues. However, at the end of the incubation more CO₂-C was released with the application of wheat residue indicating differences between residue types in the pattern of soil respiration. Microbial biomass C was higher for incorporated than mulched residue treatments; pea residue showed the highest biomass C for incorporated (0.78 mg C g⁻ ¹ soil) whereas mucuna had the highest microbial biomass (0.11 mg C g⁻ ¹ soil) treatments. The method of residue application resulted in a significant difference in C turnover between residues, with pea residue showing significant increase in C utilisation than mucuna and wheat. The pea residues, which had the lowest C:N, increased soil mineral N more than other treatments in both incorporated and mulched treatments. Lower mineralisation of N observed in residues of high C:N ratio compared to the control could be due to immobilisation of N. Therefore, understanding the nutrient dynamics of different crop residues could play an important role in the management of residues in different soil types. Based on these results it can be concluded that legume residues have the potential to improve soil fertility and crop yields in dryland farmers’ fields in Limpopo. Extension programs aimed at increasing farmers’ knowledge of the benefits of N fixation by legumes may increase their adoption and thereby improve soil fertility and maize yield. / Thesis (M.Ag.Sc.) -- University of Adelaide, School of Agriculture, Food and Wine, 2010

In Limpopo Province of South Africa, poor soil fertility and low crop yields are serious problems facing resource poor smallholder farmers. A survey of over 60 farmers in 2 villages (Gabaza and GaKgoroshi) found that most of the smallholder farmers were women (68%), elderly (50% above 68 years of age) and had not attended school or only attended up to the primary level (80%). Very few farmers kept livestock (usually in small numbers) and most grew cereal and legume crops (on 1ha of land) for home consumption and livestock feed, with legumes being planted on 13% of the land. The study showed that 80% of farmers were not fully aware of the benefits of legumes in fixing nitrogen (N) and improving yield. A field study at the survey village of Gabaza found that the application of fertiliser N and grass mulch combination and fertiliser N plus guarbean mulch significantly increased plant height and maize shoot growth at 4 and 8 weeks after planting. However, when grass mulch was without N fertiliser, there was no increase in maize growth relative to the control (0N). A farming systems simulation model (Agricultural Production Systems sIMulator - APSIM) was used to simulate this field study as well as over the long-term (1971 to 2008). Simulation analysis showed poor average maize yield (<3000 kg ha⁻ ¹) with the application of grass residues even when used with 30 kg N fertiliser. However, the application of guarbean residues as mulch with or without N fertiliser and as green manure increased maize yields to >4000 kg ha⁻ ¹. Simulation showed that the grass mulch with or without the addition of N fertiliser reduced water stress and soil water evaporation but increased N stress during the reproductive phase of the crop in most seasons. When guarbean mulch was used as green manure by itself, or mulch plus N fertiliser, N stress was reduced but water stress and soil water evaporation were increased which could have been due to faster decomposition of legume mulch as compared to grass mulch. Addition of N fertiliser reduced N stress to maize but increased water stress and soil water evaporation similar to the guarbean mulch because of high soil evaporation. APSIM analysis clearly showed the importance of N x soil water interactions in determining maize growth and yield at Gabaza. Therefore, two studies were undertaken in the laboratory in Australia to determine the dynamics of carbon (C) and N where residues of different qualities [canola (C:N 43), wheat (26), pea (9) and mucuna (14)] were applied to clay loam (Tarlee) or sandy (Waikerie) soils. In experiment 1, where residues were incorporated into the two soils, the cumulative CO₂-C evolution for the wheat and canola treatments at the end of the incubation period were fairly similar but significantly higher than for pea, mucuna and the control. In general, the application of residues increased microbial biomass C more than the control, with highest increases up to 1.48 and 1.56 mg C g⁻ ¹ soil for canola and wheat in Tarlee soil, respectively and 0.82 mg C g⁻ ¹ soil for pea in Waikerie soil. Even though the Tarlee soil showed greater C release than Waikerie soil, the C turnover from the residues between the 2 soils was not significantly different except for pea residues. Canola and wheat residues were found to immobilise N whereas N content increased in both soils with the application of legumes (pea and mucuna). In experiment 2, mucuna, pea and wheat residues were either incorporated or applied as surface mulches on Waikerie soil. Initially the CO₂-C release was higher for incorporated than mulched residues and CO₂-C released was higher for pea residues. However, at the end of the incubation more CO₂-C was released with the application of wheat residue indicating differences between residue types in the pattern of soil respiration. Microbial biomass C was higher for incorporated than mulched residue treatments; pea residue showed the highest biomass C for incorporated (0.78 mg C g⁻ ¹ soil) whereas mucuna had the highest microbial biomass (0.11 mg C g⁻ ¹ soil) treatments. The method of residue application resulted in a significant difference in C turnover between residues, with pea residue showing significant increase in C utilisation than mucuna and wheat. The pea residues, which had the lowest C:N, increased soil mineral N more than other treatments in both incorporated and mulched treatments. Lower mineralisation of N observed in residues of high C:N ratio compared to the control could be due to immobilisation of N. Therefore, understanding the nutrient dynamics of different crop residues could play an important role in the management of residues in different soil types. Based on these results it can be concluded that legume residues have the potential to improve soil fertility and crop yields in dryland farmers’ fields in Limpopo. Extension programs aimed at increasing farmers’ knowledge of the benefits of N fixation by legumes may increase their adoption and thereby improve soil fertility and maize yield. / Thesis (M.Ag.Sc.) -- University of Adelaide, School of Agriculture, Food and Wine, 2010

Diss. (sammanfattning). Uppsala : Sveriges lantbruksuniv. / Härtill 5 uppsatser.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Nitrification inhibitors can reduce the potential for environmental contamination of animal wastes, relatively to nitrate (NO3 -) leaching and nitrous oxide (N2O) emission. However, this strategy has not yet been sufficiently evaluated by research, especially with poultry litter (PL). Therefore, the objective of this study was to evaluate the effect of the product "Agrotain Plus" (AP), containing 81% of dicyandiamide (DCD), on the nitrification inhibition, ammonia (NH3) volatilization and carbon (C) and nitrogen (N) PL mineralization. Two laboratory experiments were conducted, using a Hapludalf soil collected in the 0-10 cm layer. In one experiment, conducted for 54 days, the treatments consisted of PL (4.7 Mg ha-1, dry basis) incorporated in the soil, without and with AP doses (3.5, 7.0 and 14 kg ha-1), and without PL or AP (control). In the other experiment, conducted for 69 days had all these treatments plus two additional treatments of CA on the soil surface, without and with AP (7 kg ha-1). The AP delayed NO3 - production in soil, and this inhibitory effect was more intense at the highest dose of AP (14 kg ha-1). NH3 volatilization occurred only when PL remained on the soil surface and was favored by the addition of AP. The AP addition increased PL C- and Nmineralization by 4 and 28%, respectively. The results of this study indicated that dicyandiamide (DCD), contained in the product Agrotain Plus, reduces the nitrification rate of PL ammonia in soil and could be a strategy to preserve the N of this organic material and reduce potential pollution of the environment. / Inibidores de nitrificação podem reduzir o potencial de contaminação ambiental de dejetos de animais, relativamente à lixiviação de nitrato (NO3 -) e à emissão de óxido nitroso (N2O). Todavia, essa estratégia não tem sido suficientemente avaliada pela pesquisa, especialmente com a cama de aviário (CA). Por isso, o objetivo do presente trabalho foi o de avaliar o efeito do produto Agrotain Plus (AP), o qual contém 81% de dicianodiamida (DCD), sobre a inibição da nitrificação, a volatilização de amônia (NH3) e a mineralização do carbono (C) e do nitrogênio (N) da CA. Foram conduzidos dois experimentos em laboratório, em solo da camada 0-10 cm de um Argissolo Vermelho Distrófico arênico. Num experimento, conduzido durante 54 dias, os tratamentos constaram da incorporação ao solo de CA (4,7 Mg ha-1, massa seca), sem AP e juntamente com as doses de 3,5, 7,0 e 14 kg ha-1 de AP, além de um tratamento sem CA e sem AP (testemunha). No outro experimento, conduzido durante 69 dias, além desses tratamentos havia dois com adição da CA na superfície do solo, com e sem adição de AP (7 kg ha-1). O AP, contendo DCD como inibidor da nitrificação, retardou o aparecimento de NO3 - no solo, sendo que esse efeito inibitório da nitrificação foi mais intenso na maior dose de AP (14 kg ha-1). A volatilização de NH3 ocorreu apenas quando a CA permaneceu na superfície do solo e foi favorecida pela adição de AP. A adição do AP aumentou a mineralização do C e do N da CA em 4 e 28%, respectivamente. Os resultados deste trabalho indicam que a dicianodiamida (DCD), contida no produto Agrotain Plus, reduz a taxa de nitrificação do N amoniacal da cama de aviário no solo e poderá constituir uma estratégia para preservar o N deste material orgânico, além de reduzir o seu potencial poluidor do ambiente.

Recent work has demonstrated that vast amounts of soil organic carbon (SOC) are redistributed and buried within Canadian croplands; however, the effects of redistribution on SOC dynamics and biological properties of the soil environment remain unknown. Because soil microorganisms are drivers of carbon (C) turnover in soil, the effects of such processes on microbial community dynamics are important in assessing the overall effects of redistribution and the stability of displaced C. This is particularly important in the face of future climate change scenarios and potential disturbances. The objectives of this study were to examine microbial community dynamics with depth and among landscape positions in an eroded landscape, and to assess C mineralization response between surface and subsurface soil layers in a depositional position. Microbial abundance was highly influenced by SOC redistribution. This was most evident in the buried backslope position where substantial soil and SOC deposition had occurred, creating a very thick A horizon (ca. 80 cm). Phospholipid fatty acid (PLFA) analysis revealed substantial concentrations of microbial biomass located at depth (30-60 cm), which was greater than PLFA concentration at the soil surface and correlated with SOC concentration. Community structure analysis demonstrated the strong influence of landscape position and depth in structuring microbial communities near the soil surface (0-20 cm). Communities in positions that were predominantly erosional were the most different from those in the depositional position, accounting for the largest amount of variation (60%) in the overall analysis. The existence of distinct microbial communities found in depositional material (0-25 cm) and within the buried A horizon (30-80 cm) in the buried backslope position indicate a strong influence of depth and redistribution in structuring microbial communities. The existence of significant viable biomass in the buried A horizon of the depositional position leads to question the persistence of highly concentrated, buried SOC over many decades. When soils from surface (0-5 and 20-25 cm) and subsurface (40-45 and 65-70 cm) depths were incubated in surface-like conditions, greater mineralization response in surface relative to subsurface soils, despite relatively similar SOC concentration, suggests that redistribution protects buried C from decomposition. Distinct microbial communities found at the onset and completion of the mineralization study between surface and subsurface soil layers may indicate the influence of microbial community structure on mineralization response. Depth was the largest source of variation in microbial community structure, and although a shift occurred after exposure to incubation conditions, the effect of depth remained the strongest influence. This work indicates that SOC redistribution strongly influences microbial abundance and community structure development, primarily driven by altered substrate gradients occurring with depth, and suggests that C is less susceptible to decomposition once buried in depositional positions.