The reported requirement for a higher weeding effort due to increased weed infestations under conservation agriculture (CA) relative to conventional mouldboard plough tillage is perceived by both smallholder farmers and extension workers as the main limiting factor to the widespread adoption of CA by smallholder farmers in southern Africa. However, proponents of CA argue that weeds are only a problem under CA in the initial two years and decline afterwards resulting in reduced labour requirements for weeding under CA. They further posit that weeds are only major problem where minimum tillage (MT) is adopted without crop residue mulching and diverse crop rotations. This thesis explores the effect of time under CA on weed population dynamics and crop growth under the recommended CA practices and actual smallholder farmer practice in semi-arid Zimbabwe. Assessment of weed and crop growth on a long-term CA experiment at Matopos Research Station revealed that the MT systems of planting basins and ripper tine were associated with higher early season weed density and biomass than conventional early summer mouldboard tillage (CONV) in both the fifth (cowpea phase) and sixth (sorghum phase) years of CA. This increased weed infestation within the first four weeks after planting in CA necessitated early weeding to provide a clean seedbed and avert significant crop yield loss. Maize mulching only suppressed early season weed growth in sorghum mostly at a mulch rate of 8 t ha-1 which is not a mulching rate that is attainable on most smallholder farms. However, the lower maize residue mulch rate of 4 t ha-1 was consistently associated with increased weed emergence and growth as from the middle of the cropping season in both crop species. The increased weed infestations under the mulch were probably due to the creation of ‘safe sites’ with moist conditions and moderate temperatures. The high weed growth under the mulch contributed to the low sorghum grain yield obtained under mulched plots. In addition, maize mulching was also associated with a less diverse weed community that was dominated by the competitive Setaria spp. and difficult to hoe weed Eleusine indica (L.) Gaertn. However, the weed community under CA was similar to that under CONV tillage with no evidence of a shift to the more difficult to control weed species. The increased early season weed growth and high weed pressure under CA meant that it was still necessary to hoe weed four times within the cropping season to reduce weed infestations and improve crop growth even after four years of recommended CA practices. Early and frequent weeding was effective in reducing weed growth of most species including Setaria spp. and E. indica demonstrating that on smallholder farms where labour is available hoe weeding can provide adequate weed control. The wider spacing recommended for use in CA contributed to the low cowpea and sorghum grain yields obtained under CA compared to CONV tillage. On smallholder farms in Masvingo District, the MT system of planting basin (PB) was the only conservation farming (CF) component adopted by farmers. There was no difference in the total seedling density of the soil weed seed bank and density of emerged weeds in the field in PB and conventional mouldboard ploughing done at first effective rains (CONV tillage). However, the first weeding in PB was done at least 15 days earlier (P < 0.05) than in CONV tillage suggesting high early season weed growth in PB relative to CONV tillage. As weed density did not decline with time in PB, weed management did not differ with increase in years under PB. Shortage of inputs such as seed and fertiliser was identified by smallholder farmers as the most limiting factor in PB crop production with the area under PB was equivalent to the seed and fertiliser provided by CARE International for most farmers. On this small area, weeds could be managed by available family labour. Double the maize grain yield was obtained in PB (mean: 2856 kg ha-1) due to improved weed management and soil fertility. However, the use of poorly stored composts was found to introduce weeds into some PB fields. The findings of this study demonstrated that weed pressure was still high and weed management were still a challenge under the practice recommended to smallholder farmers in Zimbabwe even in the sixth year of practice. There is, therefore, a need for research on the economic feasibility of using herbicides, intercropping and optimal crop density to ameliorate the high weed pressure under CA. / Thesis (PhD)--University of Pretoria, 2013. / Plant Production and Soil Science / unrestricted

This study was undertaken to develop an analytical model that is capable of predicting the torque requirements of a rotavator fitted with commercially available L-shaped blades. An analytical approach based on the limit equilibrium analysis was used to develop the proposed model. The proposed model was verified by comparing the model and measured torque requirements at predetermined rotavator blade angular positions from the horizontal for a down-cut rotavator. The study findings indicated that there was an optimum set tillage depth for each rotavator configuration and operational conditions at which the resultant horizontal thrust generated was greatest. This unique depth was influenced by the bite length. The validation of the proposed model showed that the predicted and measured torque requirements, at different angular blade positions from the horizontal, correlated reasonably well for all the set tillage depths. As the depth of tillage increased, however, the curve for the measured torque requirements exhibited a cyclic behaviour after the peak torque requirements value had been recorded. The cyclic behaviour was probably due to the re-tilling and the instability of the tool-frame carrier, which increased with the set tillage depth. The knowledge contributed by this research will afford the designers of active tillage tools a better understanding of the operations of the rotavator, particularly in deep tillage. The modelling approach, and instrumentation technique used in this research, can be extended to analyze the performance of rotavators fitted with other types of commercial blades. / Thesis (PhD)--University of Pretoria, 2010. / Civil Engineering / unrestricted

Made available in DSpace on 2016-01-26T18:56:33Z (GMT). No. of bitstreams: 1 Dissertacao Cassio.pdf: 89555 bytes, checksum: 2cb8164cead8de20efdda98a794b73c4 (MD5) Previous issue date: 2007-12-10 / Objected with this work to evalue the vegetable matter production, the accumulation of N and relation C/N of phytomass in different stages of single crops and consortiums of pigeon pea (Cajanus cajan), sorghum (Sorghum bicolor) and millet (Pennisetum glaucum). The experimental was conducted in a Experimental Farm of Unoeste, at Presidente Prudente-SP, during March and June, 2006. It was used the randomized experimental design in blocks, in the factorial scheme, with the followings treatments: sorghum monoculture, pigeon pea and millet, and consortium of sorghum + pigeon pea, millet + pigeon pea and millet + sorghum, with stages of collection at 30, 60 e 90 days after seeding. The millet was more expressive in the initial grouth velocity, so that species in consortium were dominated, and it produced more phytomass in the intercropping than in the monocultures. The best period to handle consortiums of millet + pigeon pea and sorghum + pigeon pea were at 60 and 90 days after seeding in off-season time, respectively. The consortium sorghum + pigeon pea submitted better balance in composition to straw, because there was more timing between growth velocity of both species. The monoculture of grass submitted straw with relation C/N more elevated than in the intercropping millet + pigeon pea and sorghum + pigeon pea. / A consorciação de plantas de cobertura tem sido preconizada com o propósito de conciliar a proteção do solo e favorecer a oferta de nutrientes em sistemas de rotação de culturas. Objetivou-se com este trabalho avaliar a produtividade de matéria vegetal, o acúmulo de N e a relação C/N de fitomassas em diferentes estádios de culturas solteiras e consorciadas de guandu-anão (Cajanus cajan), sorgo (Sorghum bicolor) e milheto (Pennisetum glaucum). O experimento foi realizado na Fazenda Experimental da Unoeste, em Presidente Prudente-SP, durante março e junho de 2006. Utilizou-se o delineamento experimental em blocos aos acaso, no esquema fatorial, com os seguintes tratamentos: monocultivos de sorgo, guandu-anão e milheto, e consórcios de sorgo + guandu-anão, milheto + guandu-anão e milheto + sorgo, com épocas de coleta aos 30, 60 e 90 dias após a semeadura. O milheto foi muito expressivo na velocidade de crescimento inicial, de tal forma que as espécies em consórcio ficaram dominadas, produzindo mais fitomassa nas culturas intercaladas do que em monocultivo. As melhores épocas para o manejo das culturas consorciadas de milheto + guandu-anão e sorgo + guandu-anão foram aos 60 e 90 dias após a semeadura no ambiente safrinha, respectivamente. A consorciação sorgo + guandu-anão apresentou maior equilíbrio na composição da palhada, pois houve mais sincronismo entre as velocidades de crescimento de ambas as espécies. Os monocultivos de gramíneas apresentaram palhadas com relações C/N mais elevadas do que nos consórcios milheto + guandu-anão e sorgo + guandu-anão.

Made available in DSpace on 2016-07-18T17:51:15Z (GMT). No. of bitstreams: 1 Dissertacao Cassio.pdf: 89555 bytes, checksum: 2cb8164cead8de20efdda98a794b73c4 (MD5) Previous issue date: 2007-12-10 / Objected with this work to evalue the vegetable matter production, the accumulation of N and relation C/N of phytomass in different stages of single crops and consortiums of pigeon pea (Cajanus cajan), sorghum (Sorghum bicolor) and millet (Pennisetum glaucum). The experimental was conducted in a Experimental Farm of Unoeste, at Presidente Prudente-SP, during March and June, 2006. It was used the randomized experimental design in blocks, in the factorial scheme, with the followings treatments: sorghum monoculture, pigeon pea and millet, and consortium of sorghum + pigeon pea, millet + pigeon pea and millet + sorghum, with stages of collection at 30, 60 e 90 days after seeding. The millet was more expressive in the initial grouth velocity, so that species in consortium were dominated, and it produced more phytomass in the intercropping than in the monocultures. The best period to handle consortiums of millet + pigeon pea and sorghum + pigeon pea were at 60 and 90 days after seeding in off-season time, respectively. The consortium sorghum + pigeon pea submitted better balance in composition to straw, because there was more timing between growth velocity of both species. The monoculture of grass submitted straw with relation C/N more elevated than in the intercropping millet + pigeon pea and sorghum + pigeon pea. / A consorciação de plantas de cobertura tem sido preconizada com o propósito de conciliar a proteção do solo e favorecer a oferta de nutrientes em sistemas de rotação de culturas. Objetivou-se com este trabalho avaliar a produtividade de matéria vegetal, o acúmulo de N e a relação C/N de fitomassas em diferentes estádios de culturas solteiras e consorciadas de guandu-anão (Cajanus cajan), sorgo (Sorghum bicolor) e milheto (Pennisetum glaucum). O experimento foi realizado na Fazenda Experimental da Unoeste, em Presidente Prudente-SP, durante março e junho de 2006. Utilizou-se o delineamento experimental em blocos aos acaso, no esquema fatorial, com os seguintes tratamentos: monocultivos de sorgo, guandu-anão e milheto, e consórcios de sorgo + guandu-anão, milheto + guandu-anão e milheto + sorgo, com épocas de coleta aos 30, 60 e 90 dias após a semeadura. O milheto foi muito expressivo na velocidade de crescimento inicial, de tal forma que as espécies em consórcio ficaram dominadas, produzindo mais fitomassa nas culturas intercaladas do que em monocultivo. As melhores épocas para o manejo das culturas consorciadas de milheto + guandu-anão e sorgo + guandu-anão foram aos 60 e 90 dias após a semeadura no ambiente safrinha, respectivamente. A consorciação sorgo + guandu-anão apresentou maior equilíbrio na composição da palhada, pois houve mais sincronismo entre as velocidades de crescimento de ambas as espécies. Os monocultivos de gramíneas apresentaram palhadas com relações C/N mais elevadas do que nos consórcios milheto + guandu-anão e sorgo + guandu-anão.

No description available.

Orientador: Carlos Alexandre Costa Crusciol / Banca: Ciro Antonio Rosolem / Banca: Salatier Buzetti / Banca: Heitor Cantarella / Banca: Waldo Alejandro Ruben Cabezas / Resumo: A consorciação do milho e sorgo com gramíneas forrageiras pode ser utilizada tanto para a formação de pastagens, como a formação de cobertura morta no sistema de semeadura direta. Dentre os nutrientes aplicados nas fertilizações destaca-se o nitrogênio, devido ser o nutriente absorvido em maior quantidade pelas culturas e o que mais influencia na produtividade de grãos, tendo sua dinâmica no sistema solo-planta condicionada pelo manejo. O trabalho de pesquisa constou de dois experimentos que foram instalados na Fazenda Experimental Lageado da Faculdade de Ciências Agronômicas - Campus de Botucatu, num Latossolo Vermelho, cultivado há aproximadamente 5 anos em sistema de semeadura direta. O objetivo dos experimentos foi avaliar o efeito da adubação nitrogenada na cultura do milho e do sorgo no sistema de cultivo solteiro e consorciado com Brachiaria brizantha e Panicum maximum em sistema de semeadura direta e o posterior desempenho das forrageiras. O delineamento experimental foi o de blocos casualizados, em esquema de parcelas subdivididas, com quatro repetições. As parcelas foram representadas por três sistemas de cultivo da cultura produtora de grãos (cultivo solteiro, cultivo com B. brizantha na linha de semeadura e cultivo com P. maximum na linha de semeadura ) e as subparcelas por quatro doses de nitrogênio em cobertura (0, 50, 100 e 200 kg ha-1 de N). Foram avaliados os atributos químicos do solo, as características agronômicas da cultura, os componentes de produção, a diagnose foliar e a produtividade de grãos, além da produção de massa de matéria seca das forrageiras após a colheita da cultura. Tanto para a cultura do milho quanto para o sorgo pode-se inferir que o cultivo consorciado, desde que seja implantado e manejado adequadamente não afeta a produção de grãos em razão de ...(Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Corn and sorghum intercropped with grass can be used both to pasture formation and to soil cover formation in no-tillage system. Nitrogen is prominent among the nutrients applied in fertilizations, because nitrogen is the most absored nutrient by crops and most affect the grains yield, and its dynamic in soil-plant system is conditioned by management. The research consisted of two experiments that were carried out at Lageado Experimental Farm, of Agricultural Science College, campus of Botucatu, in Red Latosol (Oxisol), cultivated to five years in no-tillage system. The objective of this work was to evaluate the effect of nitrogen fertilization on corn and sorghum and Brachiaria brizantha and Panicum maximum intercrops in no-tillage system, and the behavior of forages. The experimental design was in randomized blocks with split plot analyses, with four replications. The plot treatments consisted of three modalities of tillage of corn and sorghum (single crop, intercrop with B. brizantha in the row of sowing or and with P. maximum in the row of sowing) and the split plot of four nitrogen rates (0, 50, 100, and 200 kg ha-1 N). It was evaluated the soil chemical attributes, the agronomical characteristics of crop, grains yield, leaf macronutrients content and forages yield. The intercrop system did not affect grain yield of corn and sorghum, because it did not cause negative effects in plant nutrition and growth. Nitrogen fertilization affected grains yield of corn and sorghum independently of the cultivation system. The residual effect of nitrogen applied on corn and sorghum caused an increased forage yield of B. brizantha and P. maximum. No difference was observed among the soil chemical attributes due to different cultivation systems, because of the high fertility of the soil. The highest net...(Complete abstract click electronic access below) / Doutor

Orientador: Carlos Antonio Gamero / Banca: Silvio José Bicudo / Banca: Dirceu Maximino Fernandes / Banca: Antonio Renan Berchol da Silva / Banca: Carlos Eduardo Amgeli Furlani / Resumo: Cada sistema de manejo do solo é trabalhado de maneira própria, alterando de forma diferenciada as propriedades químicas, físicas e biológicas do solo, podendo requerer modificações nas recomendações e no manejo da adubação. Com o objetivo de avaliar o efeito da antecipação da adubação de semeadura, de dois sistemas de manejo do solo e dois espaçamentos entrelinhas no desempenho da cultura do milho, foi realizado este estudo. O experimento foi instalado e conduzido na Fazenda Experimental Lageado, pertencente à Faculdade de Ciências Agronômicas (FCA) da Universidade Estadual Paulista (UNESP), Campus de Botucatu, nos anos agrícolas de 2005/2006 e 2006/2007, em Nitossolo Vermelho Distroférrico. O delineamento experimental utilizado foi de blocos ao acaso com parcelas subsubdivididas e quatro repetições. As parcelas foram constituídas pelos sistemas de manejo do solo (plantio direto e preparo reduzido, caracterizado pela escarificação do solo por meio de equipamento provido de disco de corte da palhada e rolo nivelador/destorroador, trabalhando na profundidade entre 25 e 30 cm), as subparcelas pelas formas de adubação (adubação de pré-semeadura realizada na superfície do solo em área total antes da semeadura do milho e adubação convencional) e as subsubparcelas pelos espaçamentos entrelinhas (90 e 45 cm), totalizando 8 tratamentos. Os resultados obtidos foram submetidos ao teste de Tukey a 5% de probabilidade para comparar as médias entre os sistemas de manejo do solo, as formas de adubação, os espaçamentos entrelinhas e os desdobramentos das interações entre esses três fatores. As análises estatísticas demonstraram que o sistema plantio direto apresentou maior densidade do solo e resistência mecânica do solo à penetração, quando comparado ao preparo reduzido. Na operação de adubação de pré-semeadura os sistemas de manejo do solo... (resumo completo, clicar acesso eletrônico abaixo) / Abstract: Each soil tillage system is worked in proper way, modifying of differentiated form the chemical, physical and biological soil properties, and may require adaptations of fertilization recommendations and management. This study was conducted to evaluate the effect of sowing fertilization anticipation, two soil tillage systems and two row spacing on performance of the corn crop. The experiment was carried out at the "Faculdade de Ciências Agronômicas" (FCA), "Universidade Estadual Paulista" (UNESP), Botucatu-SP campus, from October 2005 to May 2007, in a Dystric Nitosol (FAO, 1974). The experimental design was in randomized blocks with split-split-plots and four repetitions. The main plots consisted of two soil tillage systems (no-tillage and reduced tillage with chisel plow with cut disk and planning roll, working at 25 to 30 cm deep), the split-plots of fertilizer application methods (surface fertilizer application before corn sowing and fertilizer application conventional) and split-split-plots of row spacings (0.90 m and 0.45 m), totalizing 8 treatments. Obtained results were analyzed by Tukey test at 5% of probability for comparing averages. Statistical analysis showed that no-tillage system had higher density as well as mechanical soil resistance to penetration, when compared to reduced tillage. For fertilizer application before corn sowing the soil tillage systems did not influence the traction force, bar power demanded, effective field capacity, demanded time, energy specific consumption and hourly fuel consumption; the reduced tillage showed higher area fuel consumption. For corn sowing it was observed that no-tillage system showed lower traction force, bar power demanded, energy specific consumption, hourly and area consumption of fuel. The 0.45 m row spacing showed higher traction force, bar power demanded, energy specific consumption... (Complete abstract click electronic access below) / Doutor

Pour protéger la ressource sol, il est nécessaire de prévoir les conséquences des activités humaines et du changement global sur l'évolution des sols notamment en modélisant cette dernière. Dans cette étude, nous avons démontré la sensibilité de SoilGen2.24 au climat, à l’usage des terres et à la réduction du travail du sol et identifié trois de ses principales limites, à savoir, certains processus trop simplifiés, certains processus manquants et une hypothèse de volume constant du sol. Ainsi, nous avons 1) construit le premier modèle d'évolution du sol entièrement modulaire, OC-VGEN, en intégrant dans VSoil, les processus du modèle SoilGen2.24; 2) testé différents formalismes pour certains des processus clés responsables de la distribution verticale de Corg, à savoir la distribution verticale des racines, la bioturbation et l'évolution verticale du taux de décomposition de Corg; 3) proposé un module mécaniste du changement de volume pour la modélisation de l'évolution du sol à court et moyen terme. OC-VGEN a été utilisé pour reproduire et projeter l’évolution, à l’échelle du siècle, de la distribution verticale de Corg pour des Luvisols ayant connu des historiques d'utilisation des terres et de travail du sol différents. Nous avons montré que 1) l'impact des processus de rétroaction sur la distribution verticale de Corg n'est pas négligeable; 2) l'usage des terres et le travail du sol influencent les rétroactions internes entraînant un impact indirect sur la dynamique de Corg; 3) le manque de connaissances sur les processus a une plus grande influence sur les trajectoires d’évolution des sols que les incertitudes sur les scénarios climatiques ou d'usage des terres. / Soil is a critical natural resource that inherently changes through time. To preserve the soil and protect it, it is necessary to predict the consequences of human activities and global change on soil evolution. This can be achieved using soil evolution modelling. In this study, we demonstrated the sensitivity of SoilGen to climate, land use and tillage reduction and identified three of its main limitations, namely some over-simplified processes, some missing processes and a simplifying assumption of constant soil volume. To overcome these limitations, we 1) built up the first fully modular soil evolution model, OC-VGEN, by using the process of SoilGen2.24 model in a modelling platform, VSoil; 2) tested different formalisms for some of the key processes responsible for the OC depth distribution, namely the root depth distribution, bioturbation and the depth evolution of the OC decomposition rate; 3) proposed a first, mechanistic approach to account for soil volume change in a short to medium time scale soil evolution modelling. OC-VGEN was used to reproduce and project the depth distribution of OC at a century time scale for Luvisols having experienced different histories of land use and tillage. We demonstrated that, at this time scale, 1) the impact of feedback processes on OC depth distribution are not negligible; 2) land use and tillage, beside their direct impact on the input of organic matter to soil, influence the internal feedbacks leading to an indirect impact on OC dynamics; 3) when projecting soil evolution, the lack of knowledge on the process definition has a larger influence on the projected trajectories than uncertainties on climate or land use scenarios.

No description available.

Weed control is an integral part of a successful overall production strategy in row- cropping systems and has the potential to reduce or eliminate yield losses that negatively affect profitability. Timely and correctly selected herbicide applications are the major keys for effective weed control in a majority of instances. However, there are negative factors that contribute to ineffectiveness and weed escape issues that currently lack viable options for management. Sparsely populated late-season weeds that emerge after lay-by herbicide applications and weeds that have become tolerant and resistant to traditional herbicide chemistries are of greatest concern. Historically, these weeds would have been pulled or chopped by hand or removed by cultivation, but with current production strategies built around conservation tillage and herbicide management practices, blanket disturbance of the soil through plowing is not a viable option. There is an immediate need for site-specific weed management to address these weed escapes while minimizing soil disturbance that reduces residual herbicide efficacy and lessens moisture losses that negatively effects the growing crop