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Fires are a natural and important element of lodgepole pine forests, however severe fires can adversely impact soil productivity, or a soils’ ability to sufficiently support nutrient availability and plant growth, for decades after a wildfire. Compound disturbances, for example, when fire occurrences follow severe mountain bark beetle outbreaks, may reduce ecosystem resiliency by influencing soil biogeochemical processes and destroying seed sources. Organic soil amendments are often applied to manage post-fire erosion, but they also have short-term impacts on soil moisture and nutrient retention that may enhance recovery of native vegetation. Little is known about how woody residue treatments such as mulch and biochar impact long-term soil productivity in compound disturbed coniferous forests. This research compared decade scale post-fire change in soil nutrients and understory plant cover and composition on six replicate burned hillslopes treated with 1) biochar, 2) wood mulch, 2) biochar + mulch and 4) an untreated control in a severely burned, beetle-killed lodgepole pine ecosystem in Colorado, USA. The site was in the gray-phase at the time of the 2010 Church’s Park fire and experienced significant overstory mortality. Both mulch and biochar were still evident a decade after treatment when they were resampled in 2023. Six replicate 5 x 5 m experimental plots that were moderately to severely burned and had similar pre-fire forest compositions were established in 2012, two years following the Church’s Park fire. Treatments of 37 t ha−1 of wood mulch, 20 t ha−1 of biochar, their combination, and an untreated burned control were randomly assigned within each treatment block. Soil moisture, nutrient pools, and plant cover were sampled in each plot in 2016 and 2023. As observed in the first years after treatment, mulch increased soil moisture compared to unamended controls ten years later, though it had few residual impacts on soil N or cations. Conversely, biochar amendments increased total soil carbon, dissolved organic C in soil leachate and C:N ratios in both soil and leachate. Though biochar also elevated various dissolved and extractable soil N forms, it reduced net nitrification rates. Total understory plant cover has remained at ~40% since 2016 and the amendments had no significant effects on overall graminoid and forb cover. However, biochar doubled the cover of the dominant shrub Vaccinium scoparium in areas where it occurred. Conversely, mulch reduced the cover of most common forb, Oreochrysum parryi, by more than 50%. These post-fire rehabilitation treatments had lasting impacts on water, N and C soils, and significant impacts on the abundance and cover of key understory species, but the long-term recovery of this ecosystem remains uncertain. As seen elsewhere in the Southern Rocky Mountain region where fire has burned bark beetle-killed forests, tree regeneration is extremely sparse within the burn scar and completely absent from the plots. Managers addressing changing climatic conditions and more frequent, severe disturbances would benefit from further research that evaluates whether these rehabilitation treatments enhance tree, shrub, and herbaceous plant establishment during active revegetation projects.

Southeastern peach orchards often have poor soil quality due to native soil composition, intensive farming practices and generational replanting of trees in the same locations. This study investigated using mulch amendments to improve the chemical and physical quality of soil prior to planting a new peach orchard. At the beginning of the four-year study, a single-ground municipal composted mulch was incorporated into the soil at two different rates and three cultivars of peaches, ‘Rubyprince’, ‘Julyprince’, and ‘BigRed’ were planted on berms. Thereafter, the same mulch product was annually applied to the top of the berms at two different rates to evaluate changes to soil organic matter (OM), cation exchange capacity, soil nutrients, and base saturation throughout the study. Additionally, horticultural parameters including tree growth, leaf nutrients, fruit yield, and fruit quality were assessed. Incorporating either rate of mulch generally had a positive effect on soil chemistry as cation exchange capacity, base saturation, and OM all increased, while soil pH was stabilized closer to 7. Both mulch rates generally enhanced nutrient availability, suggesting the potential benefits for peach growers looking to provide trees with non-synthetic forms of fertility. The trees in mulch-amended soils grew larger and could potentially yield more fruit at younger age from increased tree size, but initial yields only showed no decrease of yield from the treatments. However, continued observation over the orchard lifespan is needed to understand tree productivity and additional work is needed to optimize future application rates to avoid over-fertilization and to understand the farm economy.

Soil disturbance from the cultivation and intensive management of orchards in hot and humid subtropical climates can reduce soil organic matter (OM). This research explored how the addition of OM amendments impact soil and tree parameters in two field studies and how proximity to OM may elicit unique genomic response of peach roots in a split-root pot study. The first field study applied two rates of compost (1x and 2x) and subsequently reduced fertilizer applications annually to a virgin and replant orchard location. While both compost rates successfully replaced fertilizers, only the 2x rate in the replant location increased soil OM, phosphorus, and tree size compared to the control without compost over time. Larger tree size was most likely due to improved soil moisture within the compost-treated soil in comparison to the control during each growing season, but trees had similar water status and carbon assimilation when measured. In the second field study, municipal mulch (M) and poultry litter with mulch (PLM) were topically applied to cover the herbicide strip under mature trees to maintain a depth of 15 cm annually. The M and PLM treatments had similar foliar nutrient concentrations during the summer, but more nitrogen was available in the PLM treatment over time and led to excessive vegetative growth, a delay of fruit maturation, and reduced yield after three years. Both M and PLM treatments covering the soil appeared to limit soil moisture evaporation during the spring but prevented rewetting later in the growing season. Regardless, trees often had similar water status by treatment. A split-root pot study designed to understand gene expression of peach roots growing in heterogeneous OM soil environments revealed higher numbers of differentially expressed genes (DEGs) when roots were split between two different soil treatments, suggesting OM can elicit a systemic response like other abiotic or biotic stimulants. Additions of the OM amendments allowed for a reduction of synthetic fertilizer in the field, but additional studies will be required to understand the influence of OM amendments on orchard pests and pathogens, the orchard economy, and long-term changes to soil quality and soil health.

Riparian zones lie at the interface between aquatic and terrestrial ecosystems and usually have fertile soils, which play a crucial role in maintaining ecosystem productivity and biodiversity. Riparian zones are currently subject to vegetation loss and degradation due to human activities, intensification of agricultural practices, weed invasion, and global climate change. Therefore, there is an urgent need to revegetate and/or maintain the current vegetation of riparian zones. Soil nitrogen (N) is one of the most important growth-limiting nutrients and plays a crucial role in plant growth and productivity. Various management practices such as revegetation establishment, weed control methods, fertiliser applications, and/or organic amendments are practiced to sustain vegetation in riparian zones. However, management practices can alter soil N cycling. It is essential to understand the effect of different land management practices on soil N transformations, to maintain the long-term functional stability of riparian zones ecosystems. Revegetation of degraded riparian zones is considered one of the most effective measures in riparian management, which may influence soil N cycling. To date, no systematic literature review (meta-analysis) exists to assess the effects of different vegetation types and age on soil N pools regarding the revegetation of riparian zones (Chapter 2). Vegetation types along the riparian zones can be both native tree species and/or horticultural trees. The success of riparian revegetation projects with tree species currently depends on weed control to reduce the non-target vegetation competing over nutrients. I, hence, investigated the effects of chemical weed control on N cycling using glyphosate (commonly used herbicide) and organic-based herbicides including the registered products BioWeedTM, Pelargonic acid (Slasher®), and horticultural vinegar (acetic acid) compared with mulching. Additionally, there is a lack of information on how different herbicides could affect soil N dynamics and microbial community structure even after the application was ceased for at least one year (Chapter 3). Horticultural crops established within riparian zones are also one of the major land-use practices requiring large quantities of fertiliser, particularly N, and herbicide inputs. Glyphosate is commonly applied in horticultural lands and glyphosate interactions with organic amendments (e.g., biochar) remain uncertain. I explored the long-term interactions between biochar-amended soil and repeated application of glyphosate even after the application has ceased for over two years on soil microbial communities and soil N transformations are not well understood (Chapter 4). Glyphosate application is likely to be resumed even after stopping for a period of time and usually, very short-term N pools in response to glyphosate application in the presence of soil organic amendments like biochar are overlooked. Short-term N pools may have implications for long-term N management and hence it is important to understand short-term N pools with respect to treatments (Chapter 5). Therefore, my thesis specifically aimed to: (1) Examine the influence of riparian zone revegetation with different revegetation types and age on soil N pools by conducting a quantitative literature review (meta-analysis) (Chapter 2). (2) Assess and compare the effects of different organic-based herbicides (BioWeedTM, Slasher®, and acetic acid) and the commonly used herbicide glyphosate with mulch, on soil N dynamics and microbial community structure at two riparian revegetation sites up to two years repeated application of herbicides followed by one year after stopping herbicides applications (in total three years since the revegetation establishment) (Chapter 3). (3) Investigate the impacts of long-term repeated application of glyphosate (12 years) interacted with biochar (for three years) on soil N cycling, more specifically abundance of nitrifying populations such as the ammonia-oxidizing bacteria and archaea (AOB and AOA) as well as the overall soil microbial diversity and community structure (both fungi and bacteria) after two years following the cessation of herbicide applications (Chapter 4). (4) Explore how the interaction of biochar and glyphosate would immediately affect soil N transformations in short-term (in a 5-day laboratory incubation) using the 15N pool dilution techniques (Chapter 5) In Chapter 2: A meta-analysis was undertaken using a categorical mixed effect model to synthesise the results from 52 published articles. This study aimed to explore how different revegetation types (woodland, shrubland, and grassland) and revegetation age (< 3 years, 3-10 years, 10-20 years, 20-40 years, or > 40 years) would affect soil N pools. This meta-analysis revealed that revegetation of riparian zones significantly increased soil total nitrogen (TN) particularly in woodlands, which was associated with the presence of N fixing species and high litter inputs. Soil TN increased in revegetation ages between 10 and 40 years following revegetation, which might be associated with the increased soil organic carbon (SOC) inputs within those ages following establishment. Of the revegetation types considered in this study, NO3--N concentration in soil followed the order of grassland < shrubland < woodland, suggesting that woodland might be more efficient in soil NO3--N retention than grassland. However, revegetation significantly decreased soil moisture by 7.6% compared with the corresponding control, which might be associated with the selection of exotic species as dominant vegetation in riparian zone revegetation. This study provides insight into the influence of different revegetation types and age on soil N pools and soil moisture. This study also highlights the importance of revegetating riparian zones to increase soil TN, particularly in woodlands. Therefore, in Chapter 3, I used two newly established revegetation sites at (Kandanga and Pinbarren sites), planted with native wood species to investigate how different weed control methods including organic-based herbicides (BioWeedTM, Slasher®, and acetic acid) and the commonly used herbicide, glyphosate with mulch would affect soil N dynamics and microbial community structure over three years following revegetation establishment(two years repeated application of herbicides followed by one year after stopping herbicides applications). Soil samples were collected three times following revegetation establishment at months 2, 14, and 26 at the Kandanga site and at months 10, 22, and 34 at the Pinbarren site. The last sampling at the Pinbarren site (at month 34) occurred one year after the last herbicide was applied. In this study, I found that soil microbial biomass carbon (MBC) was significantly higher in response to mulch compared with glyphosate and organic-based herbicide treatments at months 26 at the Kandanga site and months 10 at the Pinbarren site following the revegetation establishment. However, soil MBC at month 34 at the Pinbarren site was only significantly higher in the mulch treatment than glyphosate and BioWeedTM. The level of MBC in glyphosate and BioWeedTM was also lower than the acceptable threshold at month 34 at the Pinbarren site. I also found that soil nitrate (NO3--N) was significantly higher in the soil treated with mulch than only glyphosate treatment at months 22 and 34 after revegetation at the Pinbarren site. Higher soil NO3--N in mulch compared with that of glyphosate could be partly explained by decreased denitrifying bacteria (Candidatus solibacter and Candidatus koribacter). However, there were no significant differences in soil NO3--N between mulch and other organic-based herbicides despite the fact that C. solibacter and C. koribacter were still lower under mulch than those of other herbicides. My study suggested that the application of mulch in the riparian revegetation projects would be beneficial for soil microbial functionality, particularly soil MBC as compared with [glyphosate and other organic-based herbicides. Additionally, this study suggested that some herbicides like glyphosate and BioWeedTM may have long-lasting effects on soil 125 microbial biomass even if they do not necessarily change microbial diversity. Hence, the long-term use of glyphosate and BioWeedTM needs to be considered with caution. Some woodlands within riparian zones are also horticultural sites where intensive weed control management practices are applied (Chapter 4). Therefore, an established horticultural site (Macadamia orchard) located in a riparian zone, with a history of repeated application of glyphosate (up to four times per annum for 12 years) was chosen to understand the impacts of repeated application of glyphosate interacted with biochar on soil N cycling. Wood-based biochar was first applied at this site in 2012 (64 months before my sampling time) at two different rates of 10 dry t ha-1 (B10) and 30 dry t ha-1 (B30) and the glyphosate had not been applied for two years before my sampling. Therefore, biochar and glyphosate applications coincided for three years before glyphosate was ceased. The results showed that soil TN was significantly higher in the glyphosate applied areas compared with those of no glyphosate, which may suggest that glyphosate may have stimulated N transformations in this study through increasing soil carbon (C) substrate resulting from the degradation of glyphosate and dieback of weeds. Similarly, no effect of glyphosate on soil microbial diversity and community structure was observed two years after glyphosate application had been ceased. However, glyphosate-treated soil had significantly higher AOB abundance than no glyphosate areas, which might be potentially associated with increased total carbon (TC). Conversely, biochar did not affect soil TN in this study, potentially due to the low TN content of the biochar used in this study (wood-based biochar), but had also significantly higher AOB abundance than those of no biochar plots, potentially through stimulated N cycling. In summary, neither glyphosate nor biochar impacted soil microbial diversity or community structure, but both increased AOB abundance with possible long-term implications on soil N cycling even after two years since the last glyphosate was applied. In Chapter 5, I then investigated the short-term N pools in response to the immediate interaction of glyphosate in an amended soil with biochar. I conducted an incubation study (5-day) to understand the short-term and immediate effects of glyphosate interacted with biochar on soil N transformations (ammonification, nitrification, and N mineralisation) using the 15N pool dilution techniques. Soil samples were collected from the same horticultural site used in Chapter 4. My 5-day incubation study showed that δ15N of NO3--N was not affected by any of the factors assessed including glyphosate, biochar, nd moisture content, nor were their interactions significant. However, this study showed that both nitrification and N mineralisation were stimulated by biochar. My results also showed that application of glyphosate significantly decreased δ15N of NH4+-N in soil following 3- and 5-day incubation, indicating that N mineralisation occurred, which could be related to stimulation of soil microbes due to the addition of C as a source for soil microbes resulting from the decomposition of glyphosate. In summary, my work highlighted the importance of revegetating riparian zones to increase soil N retention particularly using woodland species and showed that glyphosate and organic-based herbicides may not necessarily alter soil microbial diversity but there were long-lasting effects on soil microbial biomass observed about one year after the application being terminated. In the horticultural site, there was also an indication of both glyphosate and biochar having affected soil microbial abundance. This long-lasting effect of herbicides on soil N cycling may have implications for the long-term sustainability of riparian zones. Therefore, my work suggested that the application of mulch should be an alternative for chemical weed control when possible.

High tunnels (HTs) help producers to be more profitable through crop protection and extension of growing season. Proper ventilation and heat managements inside HTs are crucial for adjusting inner microclimates and future obtaining marketable crop production. This study first analyzed daytime ventilation rates that responds to the changes of external weather conditions in a Gothic-type HT located in eastern Tennessee. A mathematical energy balance model and instrumental measurement serve as validation data were developed with a good agreement for ventilation rates (R2>0.70). The coupling of energy balance model and air-flux calculation based on external weather parameters can be considered a valuable method to predict the interior microclimate condition and also can be used to estimate door opening levels. Also, this study using an advanced artificial neural network (ANN) discovers a better structure of HT ventilation models, and input sensitivity revealed that relative humidity and wind direction had the least significant impact on the prediction of inside air temperature. The result shows that ANN is more strongly effective than the previous theoretical model in the estimation of HT ventilation rates and opening levels. Moreover, A three-year experiment assessed the beneficial effects of independent and combined practices on temperature changes inside the HTs, and further examined the impact of temperature changes on crop production. Specific practices included surface mulches, row covers, cover crops, and irrigation water types. Statistical differences were analyzed in a randomized complete block design for total marketable yields of spring pepper and fall lettuce, as well as the changes in soil and air temperature. Black polyethylene mulch is highly recommended for pepper and lettuce production in HTs. Unfortunately, the benefit of cover crop to improve soil health was not found in this study, although there was a positive soil temperature rise surrounding plant root-zones caused by cover crops. Moreover, row covers continuously added protection from freezing during the cold nights resulting in a higher crop production. Stored rainwater was warmer than the city water except in the cold period, and rainwater irrigation is tended to increase the overall production of pepper but lettuce yielded better by using city water.

Situated on the western edge of Africa's harsh Sahel region, Senegal faces a number of agricultural production constraints. Limited rainfall, poor soil fertility, and insufficient agronomic inputs all contribute to low yielding millet production systems. This study was initiated to assess the potential for intercropping either cowpea (Vigna unguiculata (L.) Walp.) or mungbean (Vigna radiata (L.) Wilczek) into traditional pearl millet (Pennisetum glaucum (L.) R. Br.) cropping systems. During the 2013 and 2014 growing seasons two varieties of cowpea (upright and viney), and one variety of mungbean (upright) were grown in monoculture and subsequently intercropped with millet to evaluate the potential for increasing millet and overall yields. Millet was also planted with a mulch (2 t/ha of neem leaves) to test the effectiveness of increased ground cover on millet yields. In addition to yield data, soil moisture and plant NDVI data were also collected. Millet grain yields increased when intercropped with either cowpea or mungbean compared to millet that was grown alone, with grain yield increases of up to 55%. Additionally, the combined grain yields (millet + bean) were up to 67% higher than the traditional monoculture millet. The addition of mulch was the most effective treatment and increased millet grain yields up to 70%. Soil moisture increased up to 14% in mulched treatments over millet monoculture treatments. All yield increases were achieved without the addition of fertilizers or nutrient amendments. In an attempt to mimic local practices our experiment was rainfed and no soil amendments were introduced.

As urban land expands across the globe and impervious surfaces continue to be used for constructing urban infrastructure, stormwater treatment costs and environmental damage from untreated stormwater will rise. Well designed urban landscapes can employ trees and soils to reduce stormwater runoff flowing to streams and treatment facilities. Typical urban soil, however, is compacted and restricts tree growth via high soil strength and inadequate gas exchange. A site preparation method that deeply incorporates compost and includes trees for long term carbon input and pore development was evaluated in the urban setting of Arlington, Virginia. Three species were used in that study of 25 streetside plantings. The site preparation affected soil at 15 30 cm by lowering soil bulk density by 13.3%, and increasing macro-aggregate-associated carbon by 151% compared to control plots, and resulted in 77% greater tree growth during the first year after transplant. In a second experiment, rainfall simulations were used to evaluate common landscape mulch materials for their ability to prevent compaction from traffic as well their affect on surface runoff before and after traffic. When plots were subjected to heavy rainfall, (>97 mm/h) mulches were found to reduce sediment loss 82% and 73% before and after traffic, respectively. Runoff rates from wood chips were only 0.19 ml/s faster after traffic while rates from bare soil and marble gravel with geotextile increased 2.28 and 2.56 ml/s, respectively. Management of soils, trees and landscapes for stormwater benefit could reduce cost of wastewater treatment for municipalities and can prevent environmental degradation.

The rise of Industrial Revolution in the 19th century has brought not only fast economic growth, but also the release of large amounts of anthropogenic compounds into the environment. Trichloroethene (TCE), a confirmed human carcinogen, is one of the most commonly found contaminants in groundwater, therefore the remediation of this compound has been extensively studied and practiced in the past several decades. For compounds like TCE that are highly oxidized, destruction by reduction reactions (called reductive dechlorination) is more favorable than oxidative reactions. Although a wide range of bioremediation methods have been applied, biological permeable reactive barriers, referred to as biobarriers are attractive for shallow groundwater contamination plumes because of their ability to capture groundwater contaminant plumes before they migrate offsite, and their low cost of operation and maintenance. However, little research has explored the ability of biobarriers to reach complete dechlorination of TCE in oxygenated groundwater. Additionally, the dissolved oxygen in groundwater has not been taken into consideration when estimating the longevity of a biobarrier, and the impact of dissolved oxygen to the dechlorination process in a biobarrier is unknown. For this Master's thesis, a column study was conducted to study the capacity of a mulch biobarrier to fully dechlorinate TCE to ethene. Six mulch (pine bark) filled columns (2 control, 4 experimental) were constructed to study the dechlorination process of TCE, with the inoculation of KB-1TM enrichment culture (at a 1:1000 dilution level). The 1 mg/L TCE-containing v inflow water was oxygenated, to examine the impact of dissolved oxygen on mulch column performance. The mulch columns (with a hydraulic residence time of 3.3 days) were able to reduce the dissolved oxygen concentration from 7.9 mg/L to a level anaerobic enough to allow reductive dechlorination to happen within three cm into the columns. Four days after inoculation, cis-1,2-dichloroethene appeared in the columns and 8 days after inoculation, vinyl chloride showed up in trace amounts. Until 130 days of operation, levels of vinyl chloride or ethene remained low, but the dechlorination process then accelerated. By Day 212, two of the four inoculated columns reached 73% and 99% complete dechlorination (i.e. ethene comprised over 73% of the chlorinated ethenes detected at the effluent ends of the columns), and by Day 297, the other two columns also reached 95% and 99% complete dechlorination. The longevity of the column was predicted to be 7 years, considering only the impact of dissolved oxygen on the consumption of mulch-derived electron donors. Using column parameters and results from another researcher's studies, a dissolved oxygen penetration front speed of 0.7 cm of column height per month was predicted-corresponding to 5 cm within 212 days. With time, signs of TCE penetration was observed in the four inoculated columns, suggesting oxygen intrusion further into the columns. From PCR tests on DNA extracted from column liquids, the existence of key KB1 dechlorination populations, Geobacter and Dehalococcoides, were confirmed using the biomarker genes pceA for Geobacter and vcrA/16S rRNA for Dehalococcoides. qPCR tests failed to quantify these populations, but results with 16S rRNA gene primers suggested 100 to 100,000 times more 16S rRNA gene copies (not specific to known inoculated dechlorinators) vi were associated with the mulch-attached biofilms than with planktonic phases (in column liquid). vii

Small-scale urban agriculture production has become increasingly prevalent in the United States, due to an increased availability of abandoned property and demand for locally grown products. As with most agriculture production, weed suppression is a major concern for urban growers. Mulch is ideal for managing weeds because it is inexpensive and readily available. A variety of mulches have been found successful in conserving soil moisture, moderating soil temperature, suppressing weeds, and improving crop performance. These include continuous mulches such as black plastic, and particulate mulches, such as residues from cover crops. Disadvantages of black plastic, the industry standard, include impermeability and difficulty of removal and disposal. Alternatively, newspaper end-rolls (the unprinted remains of the newspaper printing process) may be a good alternative to black plastic in that they are permeable and biodegradable. However, newspaper has a high C:N ratio which can reduce soil fertility and crop growth. The primary disadvantage of plant residue is the large quantity necessary for adequate weed suppression, but combining newspaper and plant residues may provide adequate weed suppression with reduced mulch material and a lower C:N ratio. The objective of this research was to compare two continuous (sheet) mulches, newspaper and black plastic, with and without an underlying particulate mulch of killed cover crop. Field studies were conducted in 2011 and 2012 to determine the effects of mulches on soil moisture, soil temperature, weed growth, weed removal cost, and collard (Brassica oleracea L.) performance in a low input production system. Mulch treatments were newspaper alone, black plastic alone, cover crop alone (no overlying sheet mulch), newspaper + cover crop, black plastic + cover crop, and a control (no cover crop or sheet mulch). A 60:40 mix of cowpea [Vigna unguiculata (L.) Walp.] (84 kg ha-1) and buckwheat (Fagopyrum esculentum Moench) (107 kg ha-1) was planted on June 7, 2011 and May 18, 2012, and was used based on the species' rapid growth and low C:N ratio. The cover crop treatments were killed with a tractor-mounted undercutting crimper attachment eight weeks after planting. In the sheet mulch treatments, a single layer of black plastic or two layers of newspaper were rolled over the cover crop residues or bare soil and anchored with soil and/or staples. Collards were transplanted after mulches were established at 24 plants plot-1 (August 5, 2011 and June 29, 2012). In general plots with newspaper sheet had lower soil temperature and higher soil moisture than black plastic. Adding newspaper over cover crop alone improved weed control and reduced hand weeding costs compared to cover crop alone. Plots with newspaper sheets yielded as well as plots with black plastic. The addition of a cover crop had no effect. Newspaper alone or the combination of newspaper + cover crop mulch should be considered for further research because of its positive impact on soil moisture and soil temperature and its potential to suppress weeds and improve crop performance with modifications to cover crop management practices.

Growing interest in sustainable, local food production has created incentives for crop producers in urban areas to grow food for local consumption using low chemical inputs and sustainable or organic management techniques. Weeds represent a major obstacle to any organic crop production system and for small-scale producers in urban environments there is a need for organic weed control methods that are inexpensive, sustainable, and effective. Mulch has been successfully used for weed control in numerous fruit and vegetable crops. Cucurbita pepo has a high pollination demand and the native, ground-nesting bee, Peponapis pruinosa, provides the majority of the crop's pollination requirement. Peponapis pruinosa nests directly in crop fields and the nests can be disturbed by tillage operations used for weed control. Mulches that utilize municipal waste materials may provide a sustainable weed control strategy for application in urban C. pepo plantings that is more benign to P. pruinosa than tillage. Novel mulch materials remain to be investigated for their effects on weed suppression, crop performance, crop nectar and pollen production, and bee nesting. Field and greenhouse studies of pumpkin and zucchini were conducted in 2011 and 2012 to determine the effects of polyethylene black plastic, woodchips, shredded newspaper, a combination of shredded newspaper plus grass clippings (NP+grass), and bare soil on soil characteristics, C. pepo pollination, fruit production and overall crop performance, weed abundance, pest and disease pressure, and P. pruinosa nesting. Woodchip, newspaper and NP+grass mulches conserved soil moisture, with newspaper mulch resulting in the highest and plastic in the lowest soil moisture levels overall. NP+grass mulch accumulated the most soil growing degree days over the course of a season and had a positive effect on pumpkin and zucchini plant growth, producing plants greater in size and with higher leaf chlorophyll content than plants grown on bare soil. All mulch treatments resulted in higher pumpkin yield than bare soil. Misshapen, unmarketable zucchinis occurred more frequently in black plastic than in the other mulch treatments. No measurable differences in floral resource production or crop pollination were found among mulch treatments, so misshapen fruits present in black plastic may have been due to high soil temperatures. During the critical period for weed control, four to six weeks after planting, suppression of weed biomass ranged from 74% by NP+grass to 100% control by black plastic in 2011, and from 99% in woodchips to 100% control by plastic, newspaper, and NP+grass mulch in 2012. NP+grass mulch may have been compromised in 2011 due to wet weather conditions leading to more rapid degradation of grass clippings and higher weed emergence. Bee nests were located within bare, newspaper, and NP+grass plots, so P. pruinosa nesting was not prevented by these mulches. Shredded newspaper and shredded newspaper combined with grass clippings should be considered for further research because of their potential to increase sustainability within urban agricultural systems by providing adequate weed suppression and improving crop performance of C. pepo with no apparent negative impacts on pollination or P. pruinosa nesting.

The popular broadleaf herbicide atrazine is often found in contaminated groundwater along with other agricultural chemicals, such as nitrate. Mulch biowalls, a passive treatment placed in situ, can inexpensively remediate groundwater by intercepting and treating a contaminant plume. Three types of organic mulch: cedar, cypress, and hardwood were evaluated for their ability to act as supporting materials for a biowall to simultaneously remove atrazine and nitrate from groundwater. Physical and chemical properties of the mulch were characterized. Cedar mulch had the highest organic carbon content, 996 mg/g. The adsorptive capacity of the mulch for atrazine and nitrate, in mono and binary adsorbate systems were evaluated in a series of isotherm experiments. There was no statistical difference in the ratio of qe/Ce (equilibrium concentration on the mulch/equilibrium concentration in solution) for atrazine or nitrate among the three types of mulch, except for atrazine in the pairs of cedar-hardwood and cypress-hardwood in the binary adsorbate system. Atrazine adsorption appeared to exhibit a C-type isotherm, due to the range of concentrations examined; A wider range of atrazine concentrations may show a more distinct L-type isotherm. Atrazine adsorption was not affected by the presence of nitrate. Nitrate adsorption did not clearly exhibit a specific isotherm type and was affected by surface properties of the mulch as well as the presence of atrazine. The adsorption behaviors of atrazine and nitrate were quantified from Langmuir and Freundlich isotherms. Atrazine adsorption was best modeled by the Freundlich isotherm, while nitrate adsorption was best modeled by the Langmuir. Qualitatively, cypress mulch exhibited the greatest sorption capacity for atrazine and nitrate and was selected to examine the feasibility of a mulch biowall using a laboratory-scale biotic column. The cypress column was not able to remove nitrate because the concentration of dissolved oxygen was too high, even after the addition of an external carbon source. The column was not able to remove atrazine because the concentration of nitrate was too high for bacterial degradation of the herbicide to occur. Advisor: Mohamed Dahab

A combination treatment (AFM), designed to decompact and amend urban soils, and its individual components (air tillage, fertilizer, and mulch) were tested to determine their effects on fine root morphology. The site was an urban area located in Anderson, SC and included 50 red maples (Acer rubrum) growing in compacted, nutrient poor soils. Treatments were installed in November 2005, and data was collected through summer 2008. Data collection included minirhizotron images, soil moisture readings, soil temperature readings, and pre-dawn leaf water potentials. The AFM treatment had the lowest root production, root standing crop, and median root lifespan. The AFM treatment had the highest rate of root turnover. Median root lifespan for the AFM treatment was 248 days, followed by the mulch-only treatment which had a median root lifespan of 434 days. Median root lifespan for all other treatments exceeded 800 days. The mulched plots (AFM and mulch-only) had significantly higher soil water content and foliar leaf water potentials during periods of summer drought. Overall, the AFM treatment produced and maintained the fewest number of roots, had the highest rate of root turnover, but provided the most improvements to previously measured soil parameters as well as overall tree appearance and performance.

European type grapes (Vitis vinifera L.) account for over 90 % of all grapes grown in the world. However, an extra so-called “winter-hilling” practice is required for winter protection of grafted vinifera grapes in northern states including Ohio. Winter hilling consists of two tillage activities. The first is to mound soil up to cover the graft union in fall for protection from lethal cold temperatures during winter, and the second is to remove the mounded soil in the next spring for prevention of rooting from the vinifera scion. Due to the intensive soil disturbance associated with winter hilling, any vineyard along a hillside is facing elevated risk for severe soil erosion. Along with soil erosion, any chemicals applied into the vineyard, such as fungicides, insecticides, herbicides and fertilizers, are also more likely to runoff during heavy rainfall. Loss of the fertile surface soil harms grapevines, and offsite movement of chemicals pollutes the environment. Therefore, there is a great research need to find a potential substitute to winter hilling.In this study, we used simazine treated mulches (STM) to replace winter hilling and explored the following aspects: 1) weed population shifts as affected by winter hilling, 2) the efficiency of STM on weed control and herbicide resistant weed management, 3) grape production variables as affected by STM, including winter protection, nitrogen nutrition, fruit yield and quality, and 4) the potential of mulches as a mitigation tool to reduce chemical offsite movement. The results indicated that winter hilling increased the number of weed species and density in vinifera vineyards relative to vineyards that had not been hilled. STM overall provided outstanding weed control, largely due to the season-long weed suppression by mulches. Pre-winter application of simazine herbicide resulted in little residual activity by the next spring, and simazine reapplication made in June controlled weeds but was not sufficient for the balance of the growing season. Triazine resistant (TR) common lambsquarters became more prevalent in response to simazine treatment, contributing to the low efficiency of simazine on weed control. However, simazine treated bark suppressed common lambsquarters and did not result in accumulation of a more TR population. These results suggested that STM could be used as a tool for management of TR weeds in vineyards. STM protected the graft union through winter and conserved soil moisture. The effect of STM on grape yield varied on different varieties from year to year, but overall STM either had no effect or increased grape yield. The fruit quality of grape was not affected by STM with the exception that sugar content in juice of Auxerrois was lower than un-mulched treatment one of two years. Lastly, the in-lab simulation trial indicated that straw reduced simazine leaching and runoff by 40 % and 68 %, respectively, after intensive simulated rainfalls. These results indicated that mulches could be an effective tool to mitigate chemical offsite movement from the vineyard. In conclusion, STM is an integrated management tool with multiple beneficial impacts including winter protection, soil conservation, weed control and chemical runoff mitigation.

Phytophthora root rot of Fraser fir caused by Phytophthora cinnamomi and several other Phytophthora spp. is a severe problem in Christmas tree production. Since fungicides are ineffective in disease control and host resistance is not yet available, cultural control methods are under investigation as a means of reducing disease pressure on infested production sites. Mulching systems with raised beds of pine bark, wood chips, or wood chips blended with compost were tested, along with compost or sulfur as soil amendments, at five sites spanning the western North Carolina growing region. Microbial populations and activity in soils and mulches were characterized over a two year period, using dilution plating with calculation of a log series diversity index for counts of bacteria, fungi, and cellulose-degrading micoorganisms, analysis of fluorescein diacetate hydrolysis for estimation of total microbial activity, and quantification of reducing sugars after incubation with carboxymethyl-cellulose for estimation of total cellulase enzyme activity. Bacterial and fungal counts, microbial activity, and cellulase activity were higher in mulch than in soil at all sites and times (P

The application of mulch products to disturbed soil is frequently used to decrease soil erosion. The addition of polyacrylamide (PAM) has been demonstrated to reduce erosion even further. We conducted rainfall-simulator and field tests on several types of mulch, hydromulch, and erosion control blankets with varying rates of PAM to determine the relative improvements in erosion control and vegetative establishment achieved by different groundcovers and PAM. We also compared applications of granular (37 and 74 kg ha-1) and aqueous (37 kg ha-1) PAM with straw. The tests were done on 2- x 1-m soil boxes tilted to 32% slope and three field locations with similar slopes. Under simulated rainfall, the addition of 37 kg ha-1 aqueous PAM to any mulch type tended to reduce runoff turbidity, TSS, and sediment loss, with reductions of 50% or more in some cases. In the absence of PAM, increasing hydromulch rate from 1971 kg ha-1 to 2957 kg ha-1 significantly reduced turbidity for an experimental cotton product but not for wood fiber. Granular PAM, when applied at a rate equal to that of aqueous PAM, had a significantly higher mean turbidity and TSS; total sediment loss was reduced by dry-PAM only at the higher rate. The lower rate of granular PAM apparently did not reduce erosion but did flocculate the sediment captured in the runoff collection bucket, reducing turbidity. In field experiments, bonded fiber matrix had significantly lower biomass and vegetative cover than all other treatments at one site but differences were not significant at other sites. In one instance where a cotton fiber matrix test product washed off the slope face, runoff turbidity and TSS was significantly higher than other treatments. There were no instances of straw with PAM significantly improving biomass or vegetative cover compared to straw alone.

The land available for new hardwood plantations in southeast Queensland, Australia characteristically has low soil moisture availability and fertility. Establishment silviculture, such as mulch and weed control, is being used to overcome soil nutrient and water limitations during the establishment phase of hardwood plantations. However, the soil and tree physiological responses to mulch and weed control can vary widely since specific responses to such treatments in any particular stand will be the result of complex interactions of site condition, tree species, and climate. Spotted gum (Corymbia citriodora subsp. Variegata (F. Muell.)) and blackbutt (Eucalyptus pilularis Smith) are currently recommended for plantation development because they have good wood quality, good market potential and are expected to grow well on a range of sites in south-east Queensland. In this study, a series of closely related field experiments have been conducted to evaluate the effects of mulch and weed control on soil and tree physiological properties in the two establishing hardwood plantations.

The influence of reflective mulch on Pinot noir grape and wine quality was investigated over the 2004-2005 season at Upper Moutere in Nelson, New Zealand. This trial used mussel shells as a reflective mulch to improve the balance of ripening in Pinot noir. The mussel shell mulch had numerous effects on vine performance and sensory characteristics of the resulting wine. The mussel shell mulch affected numerous environmental, vegetative, phenological, yield and flavour parameters. Soil temperature was lower under the mulch by an average of 0.9°C, 1.4°C and 1.2°C. Canopy temperature was greater above the shell treatment by 1°C for an average of 7.1 hours per day. Soil moisture retention was increased under the shell mulch. The shell mulch increased reflected UV-B radiation on the canopy by four fold over the control. Soil analysis showed zinc, iron, manganese and aluminium all decreased compared to the Control. Microbe population under the shell mulch was reduced compared to the control. Early season shoot growth was greater in the shell mulch treatment than the control by 6.5 cm and 4.6 cm, respectively. Canopy vigour measured by Point Quadrat was not significantly different between treatments. Leaf SPAD readings were higher in the shell treatment during the ripening period by an average of 3.45 and 2.5. Pruning weights were not significantly different in 2004, however increased for mulched vines by an average of 0.19 kg. Budburst was not affected by treatments in 2005. Shell mulch advanced both flowering and veraison date during the season. Treatment influences on yield parameters were varied. Clusters numbers and berry weights were not significantly different at harvest in 2005. However, bunch weights were significantly different with the control bunches an average 13.1g heavier than those from the shells treatment. Ripening analysis from veraison to harvest showed similar brix and pH measures, however on the first sample date fruit sampled from the shell treatment had TA 2g/l less than the control fruit sample. This early difference was reduced to zero by harvest. HPLC analysis showed the fruit sampled from the shell treatment accumulated flavonols and anthocyanins differently than the control, although at harvest and in the resulting wine no differences were found through HPLC or spectrophotometer analysis. Wines were made on two separate scales - controlled micro-vinification and commercial scale and tasting notes of each are included. Analytically wines and fruit are similar; however, distinct sensory differences are evident: As a young wine, the shell treatment has a more vibrant richer and more complex fruit structure, more into the black cherry spectrum as opposed to a red cherry character seen in the control wines. The control wine is perceived to be more one-dimensional than the shell wine and the shell treatment wine is considered to have less green and grippy tannins than the control wine. These differences tend to reduce as the wines age.

Organic mulches and cover crops mulched in situ were assessed for their effects on B. cinerea primary inoculum and disease levels in inflorescences at flowering and/or bunches at harvest. Organic mulches were used to enhance biological degradation of vine debris to reduce levels of B. cinerea primary inoculum the following season. Four mulch types (anaerobically and aerobically fermented marc (grape pressings), inter-row grass clippings and shredded office paper) were applied under ten-year-old Riesling vines in a ten-replicate randomized block design in New Zealand over two consecutive years. Plastic mesh bags, each containing naturally infected vine debris, were placed under vines on bare ground (control) and at the soil-mulch interface, in winter (July) 2003 and 2004. In each year, half the bags were recovered at flowering (December) and the remainder at leaf plucking (February), for assessment of B. cinerea sporulation from the vine debris and debris degradation rate. Bait lamina probes, which measure soil biological activity, were placed in the soil-mulch interface three weeks before each of the two bag-recovery dates in both years and were then removed and assessed at the same times as were the bags. All mulches led to a reduction in B. cinerea sporulation. This reduction was significantly correlated with elevated rates of vine debris decomposition and increased soil biological activity. Over both years, compared with the controls, all treatments gave a 3-20-fold reduction in B. cinerea sporulation, a 1.6-2.6-fold increase in vine debris degradation and in the two marc and the paper treatments, a 1.8-4-fold increase in activity of soil organisms. The mulches also altered vine characteristics and elevated their resistance to B. cinerea through changes to the soil environment. Functional soil biological activity, as measured by Biolog Ecoplates and bait lamina probes, was increased 2-4 times in the two marc and paper treatments, compared with the control, an effect relating to the elevated soil moisture and reduced temperature fluctuations under these mulches. Soil nutrient levels and the C:N ratios were also affected in these treatments. The mulched paper lowered vine canopy density by up to 1.4 times that of the other treatments, an effect which probably led to elevated light penetration into the canopy and consequent increased canopy temperature, photosynthesis and lowered canopy humidity. These changes to soil and vine characteristics increased grape skin strength by up to 10% in the paper treatment and sugar concentrations by 1.2-1.4 °Brix in the two marc and paper treatments. The severity of B. cinerea infections in the anaerobic marc, aerobic marc and paper treatments were reduced to 12%, 3% and 2.2% of the control, respectively, in field assessments averaged over two consecutive harvests. Cover crops mulched in situ had similar effects to those of the organic mulches, increasing soil biological activity and reducing B. cinerea primary inoculum and the severity of B. cinerea infection in grapes at harvest (2006). Inter-row phacelia and ryegrass were mulched in winter 2005 and compared with a bare ground control, under 10-year-old Chardonnay vines in a ten-replicate randomized block design. Functional soil biological activity increased by 1.5-4.5 times in the two cover crop treatments compared with the control, an effect possibly related to elevated soil moisture in these treatments. This increase in soil moisture and soil biological activity increased vine debris degradation, reduced B. cinerea primary inoculum on the debris and decreased B. cinerea severity at flowering (December 2005) and harvest (April 2006). These results show the potential of organic mulches and cover crops mulched in situ to enhance soil ecosystem services and improve the sustainability of viticultural practices.

A trial established in 2003 at Upper Moutere in Nelson, New Zealand, was used to evaluate the effect of mussel shells as reflective mulch on Vitis vinifera L. cv. Pinot noir vine performance and fruit and wine quality. Shell mulch had several effects on the environment and vine growth as well as grape and wine composition in the 2006/2007 season. Soil under mulch was cooler compared to un-mulched control, but buffered the extremes in temperatures. Fruiting zone temperature over shells was slightly higher during the day and cooler at night, showing no effect on mean hourly temperature. Shell mulch reflected greater amounts of UV-A, UV-B and PAR radiation into the fruiting zone. Shell reduced weed growth compared to control. Leaf petiole and blade samples showed higher amounts of calcium compared to control. Leaf SPAD values were higher in the shell treatment during veraison, previous and postharvest, but lower post budburst. While date of budburst was not affected by treatments, dates of flowering and veraison appeared to be slightly advanced over shells. Fruit set was similar between treatments and was considered poorer in shell bunches due to a larger population of seedless berries. Vine growth was not affected in terms of the number of nodes laid at pruning, flower cluster and shoot number pre shoot thinning, early shoot growth and lateral shoots development. Vigour was not increased by shells as demonstrated by pruning weights, canopy density and trunk circumferences being similar, though internode lengths in shell shoots were greater in 2007 and lower in 2006. Berry weights, bunch weights and vine yields were lower in shell than control, though greater berry numbers were recorded. There were slight differences between treatments in fruit and wine composition. Grape pH only varied in the middle of the sampling time, being higher the 2nd week and lower the 3rd week in shell grapes and TA was greater at harvest time. However, °Brix was only higher in shell grapes in the middle of the sampling period, being similar to control at veraison and harvest. Peduncle lignification was delayed at veraison as well as at harvest time. Shell must after crushing was greater in Brix but similar to control in pH and TA. Similarly, shell wines pre bottling showed higher alcohol and no differences for pH and TA. HPLC-DAD analyses of commercial-scale and microvin wines showed consistent differences of the individual flavonoid composition. Shell microvin wines were greater than control in quercetin and resveratrol. However, commercial shell wines were lower in epicatechin, gallic acid, resveratrol, and catechin than control. Leaf phenolic composition was also different between treatments. However, further analyses by HPLC-MS in wines as well as in leaves are necessary to identify individual compounds. Total anthocyanins and total phenolics were no different between treatments. Sensory analyses of microvin and commercial shell wines exhibited consistently lower levels of green and unripe tannins, and greater smoothness and complexity as well. Further analysis by GC-MS and HPLC-MS is warranted. Shell mulch improved sensory characteristics of the resulting wines.

Effects of site preparation methods on establishment and growth of different seedling types and clones of Norway spruce were examined in this project. Two studies were established in the southern parts of Sweden. The first study aimed at investigating the effects of mulch and scarification on growth of six clones of Norway spruce in the form of rooted cuttings. In the second study, interactions between scarification treatments, including non scarified control, mounding and soil inversion, and seedling types of Norway spruce were examined at two different locations. The three different seedling types used in the experiment were a 10 weeks old containerized seedling referred to as mini seedling, a 2 year-old containerized seedling and a 2 year-old hybrid seedling (grown both as a containerized- and a bare root seedling). Mulch and scarification reduced amount of competing vegetation. Bud break occurred earlier for cuttings planted in scarification compared to control and mulch. Gas exchange and the number of new roots were higher in planting spots covered with mulch. Mulch and scarification affected survival and growth of the cuttings after the second growing season positively. Height growth was 32 mm greater and biomass increment 6 g higher in plots treated with both scarification and mulch compared to the control. Clonal differences regarding gas exchange and growth were significant. Clone 1100 had poor biomass growth, height growth and gas exchange and the lowest amount of new roots. Clone 2136 achieved the highest biomass and height growth after two years. This clone had high gas exchange values and a large number of new roots compared to clone 1100. In this study, clonal effects on growth were greater than site preparation effects. Scarification increased survival of the mini seedlings. Differences in growth between the control and scarification treatments were relatively greater for the mini seedling than for the two larger seedling types. Interactions between seedling type and scarification method for growth indicates that the mini seedlings were able to establish faster in the soil inversion treatments compared to the larger seedling types. Comparing growth rates at the same seedling age, biomass and height growth of the mini seedlings were higher or similar as for the containerized and the hybrid seedling in all scarification treatments. At the age of 3 years in the soil inversion treatment, height of the mini seedlings was 600 mm and for the hybrid seedlings the height was 400 mm. Results from this study show that mini seedlings can grow as well as or even better than larger seedlings if they are successfully established. However, mini seedlings are more sensitive to their planting environment and proper handling is critical. Problems with frost heaving and competing vegetation can be a problem and has to be taken into consideration when choosing site preparation method.

Landfills are ideal locations for short-rotation forestry, tree-based bioremediation, and wildlife habitat reconstruction. However, tree survival is reduced by harsh growing conditions and poor soil quality. This study was designed to determine survival of various tree seedlings and effects of different mulch types and depths on edaphic properties, germination, and herb emergence on a closed landfill. In spring of 2002, five species of hardwood tree seedlings were planted in clustered plots, which received a mulch treatment. The status of each seedling and soil properties were recorded for two growing seasons. Survival and growth were species dependant. Fraxinus had the highest survival rate (70%) while Prunus performed the worst (7%). Leaf mulch (15 cm deep) increased organic matter and modified various edaphic properties after the second growing season. Mulch treatments did not significantly affect seed germination rates or aboveground herbaceous biomass when compared to non-mulched controls. Practical applications of these results are discussed.

Substantial efforts have been made in the study of occupational induced airway diseases. A strong link has been found between worker exposure to organic dust and resulting acute pulmonary spasms. The supporting studies behind this link are primarily in the industries of cotton, animal and swine farming; however, some studies have been related to landscaping type tasks (i.e. mowing, leaf blowing). The relationship between organic dust and pulmonary response is associated with respiratory irritants that are found in materials such as soil, grain, and compost, especially when these materials have become moist. Some of the culprits that have been identified as causative agents of respiratory spasms are endotoxin, fungal spores, and fungal mycotoxin. This study focused on the respiratory hazards in the landscaping industry. During the month of March, landscapers worked heavily with wood mulch, which contains many organic materials that potentially harbor the aforementioned irritants. This study measured the exposure levels of endotoxin and fungal spores in the landscaper workers' breathable space. While also measuring the pulmonary function of participants and evaluating disposable respirators as an intervention. Low levels of endotoxin and fungal spores were found in the breathable space of the participants during the two days of data collection. The users were not completely satisfied with the half face disposable respirator provided, and offered detailed feedback concerning the design and use of the respirator intervention.

In grassed-down biological and integrated fruit production (BFP and IFP) orchard treatments at Lincoln, Canterbury and Clyde, Central Otago, New Zealand, the decomposition and N release of orchard understorey residues were determined and compared across the treatments using the litterbag (100 x 100 mm, 1mm mesh size) method. At Lincoln, the experimental site was a randomised complete block with 3 orchard treatments (BFP1, BFP2 and IFP) each with 3 replicates, while at Clyde the experiment site consisted of non-replicated plots of IFP1, IFP2 and BFP orchard treatments. Litterbags of respective orchards were laid on the treelines of the orchards and retrieved every 90 days over a period of 360 - 450 days. In addition, understorey vegetation herbage dry matter (DM) production as returns to the orchard treelines, its species composition, soil fertility and soil biological properties were determined. Results obtained showed that the decomposition and N release of understorey residues followed the single exponential decay model, Y = A0 e⁻kt, (R² = 0.97 - 0.99), with decomposition and N release rate constants ranging from 6.0 x 10⁻³ - 9.6 X 10⁻³ day⁻¹ and 7.0 x 10⁻³ - 13.0 X 10⁻³ day⁻¹, respectively. The C and N half-lives of understorey residues ranged from approximately 70 - 120 days and 50 - 110 days, respectively. In general, the results showed that the residue decomposition and N release were significantly most rapid in IFP compared with BFP treatments (e.g. N release: 13.0 x 10⁻³ vs.7.0 x 10⁻³day⁻¹). In addition, the burying of residues in the soil significantly increased understorey residue decomposition and N release compared with surface placement (80% vs. 54 % in 90 days). At Clyde, differences in the rates of decomposition of understorey residues were related to the residue quality. Herbage DM return through frequent mowings was approximately 18.0 t ha⁻¹ yr⁻¹ and 7.0 – 10 t ha⁻¹ yr⁻¹ at Lincoln and Clyde, respectively, returning substantial amounts of N (503 - 572 kg N ha⁻¹ yr⁻¹ at Lincoln and 225 - 310 kg N ha⁻¹ yr⁻¹ at Clyde) back to the orchards. Herbage DM return and proportions of legume species increased in the spring summer season across all treatments. At Lincoln, in spring 1999 significantly higher amounts of soil total N and available Ca, K, Mg and P were found in treelines of BFP1 compared to BFP2. In general, soil microbial biomass C showed no significant differences between BFP and IFP treatments at both Lincoln and Clyde. At Lincoln, however, earthworm number was significantly higher in BFP1 and IFP compared with BFP2 treatment. Two incubation experiments were conducted concurrently in the laboratory at 25°C for 110 days. Experiment I was a randomised complete block design using 3 orchard understorey residues and 6 other residues (barley straw, pine bark, pea straw, spent mushroom compost, sawdust and clover residues) to determine the relationships between decomposition rates and residue quality parameters. Experiment II was a randomised complete block factorial design simulating orchard treeline surface effects of bare soil, pea straw and pine bark mulches on the rate of understorey residue decomposition. Results obtained showed that the significantly rapid decomposition of understorey residues compared to pea straw, barley straw, spent mushroom compost and pine bark was related to the high quality of orchard residues. The decomposition rate constant, k, was comparable to clover residues. In simulated treeline surfaces, the understorey residue decomposition was significantly most rapid on bare soil compared to mulched surfaces (k = 0.36 - 0.40 vs. 0.12 - 0.16 day⁻¹). The highest negative effect on the decomposition rates of understorey residues was shown by the pea straw mulch surface. It was concluded that substantial amounts of N were returned to the orchard soil annually through frequent mowing of the understorey vegetation. In general, differences observed in residue decomposition and N release rates between BFP and IFP treatments were largely due to treatment components related to treeline mulches at Lincoln and understorey residue quality at Clyde rather than the orchard system as a whole.

Agricultural knowledge has been hindered by a combination of tradition and empiricism without theory; ecology may provide a useful theoretical framework. Ecological principles were applied to the experimental study of crop-weed interactions and the influences of cropping system, site, soil fertility, and plant mulches. The findings are in five papers. (I) Weed Control and Polycultural Advantage. In two of three sites, weed biomass was less in corn-legume polycultures than in monocultures; this effect did not increase corn yield but benefited legume yield and contributed in some cases to overyielding (RYT or LER > 1). When certain relationships are in effect among crops and weeds, it is predicted that polycultural overyielding, especially in monetary terms, will be more common where weeding input is low than where it is high. (II) A Comparison of Weed Communities in Some Traditional Cropping Systems in Tabasco. Polyculture and bean monoculture reduced weed biomass compared to corn and squash monocultures. Weed species composition reflected site and cropping period more than specific crops present, therefore it is probably not as easily manipulated as weed biomass. (III) Aquatic Mulches in a Reconstructed Chinampa in Tropical Mexico. Without mulch there was low growth of both crop (corn and cowpea) and weeds, and the yield of crops in weedy plots was not significantly different from in weeded. The addition of mulch increased both crop yield and weed growth, such that weeds reduced crop yield compared to weeded controls. Under low soil fertility, the full benefits of mulch were accrued by crops only when weeds were removed. A more apparent weed-control effect of mulch is expected where soil fertility is higher. (IV) Crop-Weed Interactions: The Effects of Plant Litter and Soil Fertility. At a site with relatively rich soil in s.e. Michigan, straw mulch enhanced corn yields by suppressing weeds and allowing crops to take advantage of nutrients. Nutrient addition was not responsible for the yield enhancement. (V) The Effects of Plant Litter and Soil Fertility on Weed Communities. Straw mulch greatly decreased weed biomass and number of species. Both mulch and corn presence decreased weed biomass, crop-fertilizer-mulch constituting the best combination for weed biomass control. Fertilizer did not affect weed community composition, and the action of mulch did not depend on soil fertility.