Thesis (doctoral)--Swedish University of Agricultural Sciences, 2000. / Includes bibliographical references.

A major challenge facing agriculture today is to sustain the productivity of agricultural systems with the reduction of weed invasion. The Swartland region in the Western Cape (South Africa) is intensively cropped, producing wheat (Triticum aestivum) as the major crop. As a result of the weedy ryegrass invasion the wheat yield is reduced. In addition, ryegrass has developed resistance to grass herbicides (graminicides). This situation has increased the need to use alternative practices for controlling the invasion of ryegrass in wheat fields. In this regard, crop rotation and tillage systems were proposed as techniques to suppress the ryegrass invasion. This could thus maintain a sustainable long-term wheat production system with less application of herbicides, decreased input costs and increased total grain yield. Against this background, the effects of crop rotation and tillage were determined on ryegrass seedling emergence in a field and shade netting experiment, while seed dormancy was determined in the laboratory. The objectives were to compare the wheat production of two crop rotations with mono-cropped wheat and assess the impact on the ryegrass population in no-till and minimum tillage systems. Analyses of variance on data sets of ryegrass seeds from 2009, 2010 and 2011 were used to determine germination and dormancy percentages in laboratory experiments. The performance of laboratory treatments was evaluated on the basis of germination percentage of seeds. In the field and shade netting experiments, analyses of variance for data from 2007, 2011 and 2012 were used to determine crop rotation x tillage system response. Field and shade netting performance were evaluated on the basis of ryegrass population inhibition and stimulation respectively. Ryegrass seeds from 2009 and 2010 showed higher germination percentages (80 per cent and 73 per cent) than 2011 (42 per cent). Primary dormancy prevented high germination of newly harvested seeds as dormancy release increase with age of the seed. Results of field and shade netting experiments showed stimulation of the ryegrass weed population in wheat monoculture under minimum tillage. However, when wheat was rotated with leguminous crops under both tillage systems (minimum-till and no-till) ryegrass was significantly inhibited. It was concluded that the critical period for weed competition is the first six weeks after planting. Results from this study provide a basis for producers of cereals to make good decisions with regards to timing weed control measures. It is essential to use competitive crop sequences which will inhibit weeds. The challenge is getting this practice adopted and implemented by producers as it will promote conservation agriculture within the region. This study promotes long-term sustainable wheat production systems with an efficient weed management programme that is environmentally friendly using less herbicides within the Swartland region.

Flue-cured tobacco (Nicotiana tabacum L.) is an intensively cultivated crop that typically receives four to eight primary tillage passes before being transplanted on a raised row-ridge. Strip-tillage, a conservation tillage system that only requires tilling a small strip before transplanting, has been shown to be effective for tobacco producers in southside Virginia. The cost of fertilizer in recent years and the loss of applied nutrients has brought new attention to the impact of cover crops used in conservation tillage on the nitrogen fertilization of tobacco. A two-year study conducted at the Southern Piedmont Agricultural Research and Extension Center evaluated a strip-tillage production system on agronomic performance of flue-cured tobacco and evaluated the impact of cover crop management on soil nitrogen cycling and nitrogen uptake by plants. Treatments evaluated whether a wheat cover crop was broadcast or strip killed, topdressing a wheat cover crop with 0, 22, or 45 kg ha-1, and tobacco fertilization rates. Additional treatments included a soybean residue treatment, and a conventional tillage control. Topdressing wheat with nitrogen resulted in nitrogen being released late in the growing season. Whether a wheat cover crop was strip or broadcast killed had no effect on yield or cured leaf quality. Soybean residue did not provide adequate soil cover, but was shown to be a suitable ground cover option for tobacco production. Wheat not topdressed with nitrogen and tobacco receiving normal fertilization had adequate soil surface residue cover, good cured leaf quality, and yields that were comparable to those of conventional tillage. / Master of Science

The response of upland cotton (Gossypium hirsutum L.) to legume and small grain cover crop establishment, in-season nitrogen (N) rate, and fertilizer N placement was investigated in two experiments located in coastal plain Virginia and North Carolina. The first experiment examined 1) soil compaction and cotton yield response to strip-tillage compared to no-tillage with a precision planted tillage radish and 2) the influence of legume mix, rye, and legume mix/rye combination cover crops with four in-season nitrogen (N) rates applied to cotton on cover crop biomass, cover crop nutrient uptake, soil compaction, soil N cycling, petiole nitrate-N (NO3-N) during the first week of bloom, cotton lint yield, and fiber quality parameters over two years. Legume mix cover crops resulted in greater N uptake, soil NO3-N during the growing season, and lint yields compared to LMR, rye, and fallow treatments over both study years. Soil compaction and lint yields were not significantly different between strip-tilled and no-till with tillage radish treatments in either year. Relative lint yields after LM were maximized at 93% relative yield with 110 kg N ha-1 applied in-season while relative lint yields for cotton following LM with 0 kg N ha-1 applied reached 75%, measuring at least 9% higher than cotton following other cover crop treatments. The second experiment investigated the effect of five N rates (0, 45, 90, 135, and 180 kg N ha-1) and three placement methods (broadcast, surface banded, and injected) on lint yield, petiole nitrate-N (NO3-N), lint percent turnout, and fiber quality parameters. Nitrogen rate and placement had a significant effect on lint yield but only N rate affected petiole NO3-N concentration. It was estimated that injecting fertilizer N requires an N rate of 133 kg N ha-1 to achieve 95% relative yield while surface banded fertilizer N required a rate of 128 kg N ha-1 to produce 90% relative yield. A critical petiole NO3-N concentration threshold of 5,600 mg NO3-N kg-1 was calculated to reach 92% relative yield. Other agronomic management practices such as cover crop termination timing, cover crop species blends, and number of fertilizer N applications are of interest in order to develop better recommendations and promote conservation agricultural practices in coastal plain Virginia and North Carolina. / Master of Science / Upland cotton (Gossypium hirsutum L.) response to diverse species cover crop mixes, conservation tillage method, fertilizer N rate, and fertilizer N placement at side-dress was measured in two field studies conducted on the coastal plain soil in Virginia and North Carolina from 2016-2018. The objectives of the following research were to 1) examine the influence of two conservation tillage practices and four cover crop mixes on cover crop biomass production, soil compaction, cover crop nutrient uptake, soil N cycling, petiole nitrate (NO3-N) and cotton lint yield and 2) measure cotton performance in response to five N rate and three placement application methods. Legume mix (LM) cover crops contained more N in biomass, resulting in higher soil NO3-N during the growing season and higher lint yields at harvest compared to a legume mix and rye combination (LMR), rye, and fallow treatments. Soil compaction and lint yield were not significantly different between strip-tilled and no-till/tillage radish treatments in either year. Nitrogen rate and placement had a significant effect on lint yield but only N rate affected petiole NO3-N concentration. Injection of fertilizer N required an N rate of 133 kg N ha1 to achieve 95% relative yield while surface banded fertilizer N required a rate of 128 kg N ha-1 to produce 90% relative yield. A critical petiole NO3-N concentration threshold of 5,600 mg NO3-N kg-1 was also calculated to reach 92% relative yield. Future application of these results can include investigation of optimal N source for Virginia cotton production, best N placement method for cotton grown in high residue systems, and an economic analysis to determine optimum agronomic management for Virginia coastal plain cotton production.

Masters of Science / Department of Agricultural Economics / Hikaru H. Peterson / Concerns about environmental degradation due to agriculture have gained importance as it is associated with soil erosion, health hazards, and ground water pollution. Environment-friendly land use practices have been developed to gain a wide range of environmental benefits including reduced soil erosion, reduced nutrient runoff from crop and livestock facilities, increased biodiversity preservation efforts, and restoration of wetlands and other native ecosystems. No-till is one such practice where soil erosion, nutrient runoff and environmental degradation can be reduced to a certain extent. This study evaluated the factors affecting the adoption of tillage systems in Kansas. A survey was conducted with a total of 135 participants from four different locations in the state of Kansas between August 2006 and January 2007. The adoption process was modeled as a two-step econometric models consisting of perception and adoption equations to estimate the impacts of demographic variables and farmers’ familiarity with and participation in certain conservation programs. The results for the perception models showed that the farm operators’ perceptions regarding whether BPM installation and management is unfair to producers or not and whether environmental legislation is often unfair to producers do not vary systematically across farm size, producers’ familiarity and participation in conservation programs, or other demographics considered in the study. On the other hand, their perceptions regarding how polluted their water supplies varied by their thoughts on relative profitability across various tillage practices, their primary occupation, and their familiarity with conservation programs. Specifically, the results suggested that those who regarded no-till practices to be more profitable than other tillage practices or whose primary occupation was farming-related tended to believe that ground water was not polluted, and those who were less familiar with available conservation programs tended to believe that surface waters were not polluted. The adoption model results suggested that farmers with greater operating acreage, those who perceived that no-till was more profitable than other tillage systems, and those with greater familiarity with and participation in existing conservation programs were more likely to adopt more conservation tillage systems, all else equal. Further, perceptions of fairness of environmental regulations or the level of pollution did not impact the tillage choices.

A agricultura é a atividade humana que mais afeta o meio ambiente. Imensas quantidades de insumos agrícolas são aplicados sobre o solo e grande parte destes degrada os recursos hídricos. Para uma investigação adequada do efeito destes insumos, estudam-se as propriedades hidráulicas do solo, que influem no transporte de solutos neste meio. Medir tais propriedades e modelar os parâmetros correlatos são tarefas extremamente complexas, devido ao tempo requerido, dinheiro, instrumentação e escala. As metodologias convencionais inferem as propriedades hidráulicas em amostras que estão em equilíbrio, através de técnicas invasivas e sob restrições especiais. Esta tese contribui com a ciência do ambiente, via ciência do solo, propondo um novo método de estudo da infiltração da água na região não-saturada do solo, utilizando a tomografia computadorizada (TC). O tomógrafo foi aqui desenvolvido e construído. A TC, neste trabalho, mediu a umidade (teta) durante o fluxo não-saturado e, através da solução numérica da equação de Richards e do modelo de Rossi-Nimmo, obtiveram-se a curva de retenção, a sortividade, k(teta) e a difusividade D(teta). Resultados qualitativos, como imagens 2D e 3D, e resultados quantitativos demonstraram a boa correlação do método proposto com o método tradicional de medida da curva de retenção. Amostras de solo estrurado foram analisadas em laboratório e em campo. / Agriculture is the human activity that most affects the environment. Huge amounts of chemicals are applied on the soil. Pesticides percolation and runoff degrades water resources. Thus, soil hydraulic properties must be known due to their influence on solute transport. The measurement of these properties and the modelling of related parameters are often difficult, if not impossible, due to the involved time, money, instrumentation, and scale. Traditional methodologies infer hydraulic properties in samples that are in equilibrium, through invasive techniques and under some special constraints. This thesis contributes with environmental science, via soil science, as it proposes a new method to study the infiltration in the unsaturated zone of soil, by means of CT. The scanner was developed and constructed in this work. The proposed methodology uses profiling CT to measure the water content (theta) during the water flow, and by means of numerical solution of Richards equation and Rossi-Nimmo model water retention, sorptivity, hydraulic conductivity k(theta), and diffusivity D(theta) are obtained. Qualitative results, as 2D and 3D images, are presented and the quantitative results of water retention show good correlation of the proposed method with the conventional tensiometers method. Structured soil column samples are analyzed in the field and in laboratory.

Submitted by Erika Demachki (erikademachki@gmail.com) on 2016-03-17T19:55:19Z No. of bitstreams: 2 Dissertação - Guilherme Felisberto - 2015.pdf: 1617552 bytes, checksum: 2e18b5759b2febfc144f25537d22ab9a (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Erika Demachki (erikademachki@gmail.com) on 2016-03-17T19:56:38Z (GMT) No. of bitstreams: 2 Dissertação - Guilherme Felisberto - 2015.pdf: 1617552 bytes, checksum: 2e18b5759b2febfc144f25537d22ab9a (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2016-03-17T19:56:38Z (GMT). No. of bitstreams: 2 Dissertação - Guilherme Felisberto - 2015.pdf: 1617552 bytes, checksum: 2e18b5759b2febfc144f25537d22ab9a (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2015-07-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / There is the possibility of reduction of nitrogen fertilization in maize under no-tillage system following cover crops. In order to generate information about the subject, this work was carried out to evaluate the nitrogen fertilization in maize following cover crops in southwestern Goiás. The experiment was developed at the Universidade Federal de Goiás, Regional Jataí, under a randomized block design with four replications in split plot. Treatments allocated on plots were ten cover crops (Cajanus cajan, Canavalia ensiformis, Crambe abyssinica, Crotalaria juncea, Crotalaria ochroleuca, Crotalaria spectabilis, Mucuna aterrima, Pennisetum glaucum, Raphanus sativus and Urochloa ruziziensis), grown before maize. Treatments allocated in the subplots were four nitrogen rates (0, 50, 100 and 150 kg ha-1 of N) topdressed in the V5 growth stage of the crop, totaling 40 treatments. The water deficit limited the maize crop response to nitrogen topdressing, grown in succession to cover crops. The maize grown after Urochloa ruziziensis with simulated grazing and Crambe abyssinica showed lower yield. / Há a possibilidade de redução da adubação nitrogenada na cultura do milho sob sistema de plantio direto em sucessão a plantas de cobertura. Visando gerar informações sobre o tema objetivou-se com o presente trabalho avaliar a adubação nitrogenada na cultura do milho em sucessão a plantas de cobertura no sudoeste goiano. O experimento foi conduzido na Universidade Federal de Goiás, Regional Jataí, sob o delineamento de blocos casualizados com quatro repetições, em esquema de parcelas subdivididas. Os tratamentos alocados nas parcelas foram dez plantas de cobertura (Cajanus cajan, Canavalia ensiformis, Crambe abyssinica, Crotalaria juncea, Crotalaria ochroleuca, Crotalaria spectabilis, Mucuna aterrima, Pennisetum glaucum, Raphanus sativus e Urochloa ruziziensis), cultivadas em antecessão à cultura do milho. Os tratamentos alocados nas subparcelas foram quatro doses de nitrogênio (0, 50, 100 e 150 kg ha-1 de N) aplicadas no estádio de desenvolvimento V5 da cultura do milho, totalizando 40 tratamentos. O déficit hídrico limitou as respostas da cultura do milho a adubação nitrogenada em cobertura, cultivada em sucessão a plantas de cobertura. O milho cultivado em sucessão a Urochloa ruziziensis com pastejo simulado e ao Crambe abyssinica apresentou menor produtividade de grãos.

Dark tobacco (Nicotiana tabacum L.) has historically been produced usingconventional tillage practices. Soil is cultivated multiple times throughout a growing season leading to an increased incidence of soil erosion. No-till systems have been growing in popularity with the advent of new technology that has enabled the practice to be performed effectively and efficiently. With the recent expansion of no-till practices throughout the agricultural community, many crops have had success in producing comparable yields while reducing input costs and saving soil resources. For this experiment, a traditional tobacco transplanter was modified for use in a no-till environment. All modifications were fabricated without using specialty tools and made possible to be removed if desired or necessary. Frame extensions were designed and built to accommodate row cleaners and coulters. Tillage shanks were also added to aid in optimal furrow formation. Double-disc opening shoes replaced the original round point shoes and the curved edges of the rear drive wheels were removed, creating a flat surface to increase soil contact. Experimental no-till plots in fescue sod and soybean chaff residues were conducted alongside conventional tillage plots at the Western Kentucky University Agricultural Research and Education Complex in summer 2011. Five treatments, one conventionally tilled (Conv) and four no-till, were replicated three times within a randomized complete block design and used to determine the efficacy of transplanter modifications (consistency of depth, furrow closure, observed plant damage), survival of the transplants, and the amount of residue displacement. The four no-till treatments utilized different combinations including: coulter, row cleaner and shank (CRS), row cleaner and shank (RS), coulter and shank (CS), and shank only (S). These treatments demonstrated the functionality of each combination in comparison to conventional treatments. No treatment performed equally well in both residue locations. Plots in fescue residue utilizing a combination of coulter, row cleaner, shank (CRS), exhibited the lowest amount of root exposure, highest survival rate, and comparable cured weight when compared to conventionally tilled treatments. In soybean residue plots, the treatment operating with row cleaners and shanks (RS) had equivalent amounts of furrow closure to conventionally tilled plots. Pairing specific modification combinations with previous crop residue can provide furrow closure, transplant survival, and cured yield equivalent to conventionally tilled dark tobacco.

Long-term food security and environmental quality are closely linked to maintaining soil quality. Therefore, the assessment of the effect of agricultural management practices on soil chemical, physical and biological parameters provide fundamental information about sustainability. An agricultural management practice which has received much attention in the last decade is tillage. The loss of topsoil due to erosion and a reduction of soil organic matter under conventional tillage practices, together with escalating fuel prices, have lead to the increased implementation of conservation tillage practices. However, the response of soil to a reduction in tillage is dependent on the inherent soil properties, environmental conditions, crop type and the land management practices. The successful implementation of conservation tillage practices is thus site specific. Furthermore, the effect of fertilizer application on soil quality is affected by tillage regime and therefore has important implications for recommendations of fertilizer application rates. The objectives of this study were to investigate the effect of tillage regime at three rates of nitrogen fertilization on soil microbial activity and selected soil physical properties in the Loskop area of KwaZulu-Natal, South Africa. Based on the outcomes of these investigations, recommendations regarding sustainable tillage practice and nitrogen fertilizer application rate are made. A field trial was initiated in 2003 on Gourton Farm in the Loskop area of KwaZulu-Natal on an area that was previously under annual conventional tillage and is currently planted to dry-land maize. The trial was arranged as a split plot experimental design with tillage regime (whole plots) replicated three times, and fertilizer type and application rate forming randomized subplots within the whole plots. The trial was on a clay loam soil type (Hutton soil form). The effects of annual conventional tillage (CT1) and no-till (NT) at three rates of nitrogen (N) fertilizer (as limestone ammonium nitrate (LAN)) applied at rates of 0 kg N ha-1 annum-1 (0N), 100 kg N ha-1 annum-1 (100N) and 200 kg N ha-1 annum-1 (200N) were evaluated for their effects on soil organic carbon (SOC), microbial activity, bulk density (ñb), water retention characteristics, saturated hydraulic conductivity (Ks), micro-aggregate stability and soil penetration resistance. Undisturbed soil cores were taken from three inter-rows in triplicate from each sub-plot for the A horizon (0 to 20 cm) and from three inter-rows in duplicate for the B horizon (20 to 40 cm). These undisturbed soil cores were used to determine the ñb, water retention characteristics and Ks. Bulk soil samples were collected from three inter-rows in triplicate from each sub-plot for the A (0 to 20 cm) and B (20 to 40 cm) horizons. The bulk samples from each horizon in each sub-plot were thoroughly mixed and halved. One half was used to determine microbial activity as measured by the hydrolytic and cellulolytic activity and the other half was used to determine SOC content, particle size distribution and aggregate stability. Penetration resistance was taken in duplicate in three rows in each sub-plot at 1 cm increments to a depth of 50 cm or until an instrument limiting penetration resistance of 5000 kPa was reached. Tillage regime and N application rate considerably affected soil microbial and physical properties in the A horizon (0 to 20 cm). The SOC, hydrolytic activity and ñb are significantly greater (P 0.05) effect on the soil microbial activity and physical properties except for Ks, where the Ks is significantly (P 0.05) in the B horizon on the measured soil microbial activity and physical properties except for the penetration resistance. Increasing levels of fertilizer resulted in increased penetration resistance throughout the soil profile under NT. Under CT1, this same trend is evident from below the plough layer. These results indicate that the microbial activity, as measured by hydrolytic and cellulolytic activity, is improved under NT compared to CT1. Furthermore, the soil under NT retains more plant available water (PAW) and although the ñb and penetration resistance are greater there was no obvious adverse effect on maize growth. In addition, a high rate of LAN fertilizer adversely affected soil microbial and physical properties, especially under NT. Therefore, it is proposed that NT is the preferred tillage practice in providing long-term sustainability and soil health without causing negative soil structural properties for crop productivity in the short-term. In addition, it is recommended that although increased levels of nitrogen fertilizer results in higher yielding maize plants it is unsustainable to apply high applications of LAN due to the negative effect on the soil microbial and physical properties and thus there is a need to re-evaluate the sustainability of using high rates of LAN to increase crop yields, especially under NT systems. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

To evaluate the strip tillage in organic bell pepper (Capsicum annuum L.) production as an integrated system for sustainable vegetable cropping two-years of field trials were conducted in 2011 and 2012. The field trials were conducted to determine the viability of strip tillage in conventional and organic bell pepper production systems by comparing plant growth, water status, and fruit yield to plastic mulch grown plants application under different irrigation regimes. The two-year field data demonstrated that organic pepper with strip tillage application was a viable combination that produced comparable yield to conventional plastic mulch system and utilized water more economically. In 2011 and 2013, strip-tilled rows and plastic mulched rows were used to evaluate the impact of tillage on soil hydraulic conductivity and water internal drainage characteristics. Results indicated that strip-tilled plots had significantly higher in-row penetration resistance compared to the plastic mulch system at depths up to 20 cm, but no differences between the systems were found for layers below 25 cm. In addition, there were no differences in hydraulic conductivity between strip tillage and plastic mulch in both study years over a 30-day period. Also, significant main effects were found for soil layer and time scale on hydraulic conductivity in the first 24 hour of the study in 2013. During field trials in 2011 and 2012, plant tissues were sampled for endophytic bacteria isolation and identification. Differences in endophytic bacteria were obtained among different production combinations. In 2013, endophytic bacteria isolates from 2011 and 2012 trials were re-inoculated to bell pepper grown in greenhouse to assess plant growth. Two Pseudomonas sp. and one Bacillus thioparans strain were screened to evaluate their affects on plant growth under both drought and non-drought conditions. After growth comparisons, the three endophytic strains were used to subsequently study the impacts of endophyte inoculation on regulating plant drought-linked gene expressions in 2014 by conducting real-time PCR. Results demonstrated that plant drought-linked genes, which especially involved plant ethylene biosynthesis, were significantly down-regulated after inoculating the endophytic bacterial strains.