Maize (Zea mays L.) is one of the most important crops in South Africa that is cultivated for food, feed and as a cash crop. Maize in the Eastern Cape is typically grown for consumption and the Province is one of the least producers owing to small landholdings, poor production conditions and pests. This study investigated: (i) the different maize cropping systems smallholder farmers practice in the Eastern Cape (EC), (ii) the major maize insect pests within the identified cropping systems, (iii) the perceptions of Eastern Cape smallholder maize farmers on the effects of insect pests, and (iv) the effects of crop residues on insect pests’ population dynamics. Four major cropping systems namely: maize sole cropping without rotations by government sponsored farmers (GCP) (94 percent), maize intercropping without rotations by independent farmers (IF) (79 percent), maize sole cropping without rotations by IF (67 percent) and maize intercropping without rotations by GCP (61 percent) were identified. The choice of a cropping system by the smallholder farmers was significantly influenced by source of sponsorship, the difference in their district localities, tenure system, availability of inputs and farming equipment, percentage of farmland farmers allocate to maize, maize varieties, farming experience, fallow operations and access to irrigation facilities. The major constraints faced by the farmers in maize production are the attack by insect pests, weeds competition, drought, the lack of fencing around the fields and destruction by mammals. The major insect pests identified were stalk borers (Busseola fusca, Chilo partellus), cutworms (Agrotis spp.), aphids (Rhopalosiphum maidis), bollworms (Helicoverpa armigera) and weevils (Sitophylus spp.). The most popular control measures employed were the use of GM maize and pesticides. Results from the field trial showed that field crickets were the major ground dwelling insect pests observed followed by bollworms and cutworms. However, there were no significant influence of residue retention on the insects’ diversity indices, richness, and evenness. Above ground insects sampling revealed the domination by four major insects namely, cutworms, maize stalk borer, bollworms, and spotted stalk borer. Residue management significantly influenced the infestation by spotted stalk borer only on maize plots. However, the general trend was that there was less infestation by the insects in plots where residues were retained than the ones with residue removed. Results from the study indicate that government sponsorship is significantly influencing the maize cropping systems of the smallholder farmers of the Eastern Cape.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第20769号 / 農博第2252号 / 新制||農||1054(附属図書館) / 学位論文||H29||N5089(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 舟川 晋也, 教授 間藤 徹, 教授 縄田 栄治 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

Doctor of Philosophy / Department of Agronomy / Charles W. Rice / Biofuel feedstocks such as grains and cellulose are gaining increased attention as part of the U.S. portfolio of solutions to address climate change and improve energy security. As the future of biofuels unfolds, major concerns are emerging, including the sustainability of the soil resource in bioenergy cropping system. With a clear understanding of the sustainability risks that exist within the agricultural soil resources, it is now essential to develop metrics that document the soil health as well as the total biomass production of different cropping system. We tested the effectiveness of eight bioenergy plant species grouped between annual and perennial crops. Our main objective was to determine the sustainability of bioenergy cropping systems. There was significantly greater soil structural stability plus greater root biomass under the perennial crops but greater aboveground biomass in the annual crop. Differences in soil carbon measured to 1.2 m were not significant between energy crops after five years. A transparent, unbiased method to identify possible change in soil characteristics under bioenergy cropping practice was offered. Our next metrics were soil aggregate stability and microbial community structure as indicators of soil ecosystem health and environmental stability. The effects 24 years of differing levels of residue and fertilizer inputs on soil aggregate stability, aggregate C and microbial community structure were evaluated. A native, undisturbed prairie site, located nearby was used as a reference in this study. The results showed that greater inputs of inorganic N and increased returns of crop residues did not cause a proportionately greater increase in SOC. The abundance of microbial parameters generally followed their potential carbon pool in cultivated soils but a strong mismatch was observed in the native prairie site. Our results showed for the first time a clear disconnect between decomposers and macroaggregates; highlighting the role of soil structure in protecting organic matter. Soil carbon sequestration is one of the mechanisms that have been proposed as temporary measure to mitigate global climate change. However, there was a particularly large risk of negative effects of mitigation measures related to the increased removal of crop residues from cropping systems for use in bioenergy, if this means that soil carbon is reduced. Effective measurement of soil C at the field scale requires an understanding of the spatial variability of soil C on a landscape scale. Recent technological advances in soil C measurement offer new opportunities in this area. Our surface measurements of soil C by near infrared spectroscopy (NIRS) provided a quick assessment of soil C and, soil C predicted by NIRS and measured by dry combustion laboratory measurements was correlated with and R-squared of 0.84.

Bibliography: leaves 105-129.

The application of crop residues is one of the most common agricultural practices used to maintain soil ecosystems and crop productivity. This thesis focuses on the oil palm (Elaeis guineensis) agroecosystem, an important tropical crop that has expanded rapidly over the past four decades. Both land conversion and business-as-usual practices within the plantations have contributed to soil degradation. The application of oil palm residues, such as empty fruit bunches (EFB) and oil palm fronds, are thought to have positive effects on the soil ecosystem; yet there is currently a deficit of knowledge on their effectiveness. This thesis aims to examine the effects of oil palm residue application on soil physicochemical properties, soil biota, and ecosystem functions. It reports the results of extensive field trials, sample collection, and statistical analysis of crop residue applications in oil palm plantations in Central Sumatra, Indonesia. Four key results emerged from the thesis. First, in this study site land conversion from secondary forest to oil palm does not affect litter decomposition rate, but positively influences soil fauna activity. Second, there is greater soil fauna activity following EFB application than oil palm fronds or chemical fertilizers, and the fauna activity is highly associated with changes in soil chemical properties and soil moisture conditions. Third, EFB application enhances soil ecosystem functions, through the direct provision of organic matter, and by influencing soil biota. Finally, over 15 years of application, EFB appears to be effective in maintaining or increasing annual crop yield in comparison to chemical fertiliser treatment. Temporal changes in crop yield under EFB application appear to be associated with climatic conditions and soil organic carbon. Overall, these findings improve our understanding of the potential of oil palm residue applications to increase soil quality, soil biota, and ecosystem functions. They also provide useful information for a wider audience of soil ecologists, agricultural managers, and policy makers to improve sustainable management of the oil palm ecosystem.

There are apprehensions that genetic modification of maize with Bacillus thuringiensis (Bt) may have negative effects on soil biodiversity, ecosystem processes and functions. This study aimed at determining the effect of Bt maize crop, Bt maize residues and its genetic modification on microbial biomass carbon (MBC), selected enzyme activities, vesicular arbuscular mycorrhizal (VAM) fungi and N and P release patterns. The study was conducted under field, glasshouse and laboratory conditions. In 2010/2011 season, four maize cultivars; DKC 61-25B (Bt), DKC 61-24 (non-Bt), PAN 6Q-321B (Bt) and PAN6777 (non-Bt) were planted. Determination of MBC, enzyme activities and fungal spore count was done at 42, 70, and 105 days after planting (DAP). A loam soil amended with Bt or non-Bt maize leaf residues from a study of 2009/2010 season was incubated to investigate effects of Bt maize residues on MBC and soil enzyme activities. Leaf residues of Bt and non-Bt maize cultivars (DKC 61-25B, DKC 61-24, PAN 6Q-321B and PAN6777) were used and soil without residues was used as a control. Samples were collected at 7, 28 and 56 days of incubation (DOI). An incubation study was also carried out in the laboratory to determine the effect of Bt maize residues (i.e. leaf, stem and root) and its genetic modification on N and P release patterns. Residues of DKC 61-25B, DKC 61-24, PAN 6Q-321B and PAN6777and soil without residues as a control were incubated in the laboratory. After destructive sampling at 0, 7, 14, 28, and 56 DOI, N in the form of NH4-N and NO3-N and P mineralisation were determined. Amendment of soil with residues enhanced MBC (p < 0.05) at all the sampling dates. For example MBC increased from 95 in the control to 146.3 mg/kg in the DKC 61-25B treatment at the end of the glasshouse trial. In the field DKC 61-25B had 9.1 mg/kg greater MBC than DKC 61-24, while PAN 6Q-321B had 23.9 mg/kg more MBC than PAN6777 at the end of the trial. However, no differences (p < 0.05) were observed in enzyme activities under field and glasshouse conditions except for dehydrogenase that had greater activity where DKC 61-25B and PAN 6777 were grown. There were no differences between the type of residues (Bt and non-Bt) on enzyme activities tested. However, differences were observed among the sampling dates. No effects of Bt maize crop on fungal spore count were observed. Similarly no differences were observed in leaf, stem and root tissues composition between Bt and non-Bt maize cultivars. Net N and P mineralisation from Bt maize cultivars did not differ from that of non-Bt maize cultivars. However, differences were observed among the cultivars. The results of this study suggested that Bt maize with Bt MON810 event can be grown in the central region of the Eastern Cape (EC), South Africa without affecting MBC, soil enzyme activities, VAM, and release of N and P nutrients from its residues.

Six combinations of grazing, tillage, and herbicides were studied during 2 yr in a randomized block design to determine alfalfa (Medicago sativa) survival, corn (Zea mays) plant populations and corn growth in an alfalfa-corn rotation. Alfalfa was overseeded with rye (Secale cereale) in autumn prior to planting corn in spring of each year. Treatments were 1) non-grazed control with standard chemical treatments for no-till establishment of corn, 2) grazing alfalfa, then grazing rye until corn planting followed by dicamba application, 3) alfalfa grazing plus glyphosate prior to corn planting, 4) treatment 3 plus grazing prior to rye jointing, and 5) alfalfa grazing plus autumn application of glyphosate, 6) alfalfa grazing plus autumn disking (no herbicides). Grazing until corn planting decreased (P<0.05) alfalfa stands and rye biomass, but increased (P<0.05) corn plant populations and soil bulk density compared to shorter grazing periods. Grazing prior to rye jointing increased (P <0.05) soil bulk density and corn plant populations, and decreased (P<0.05) rye biomass compared to no spring grazing. Autumn disking decreased (P<0.05) bulk density, but generally provided less (P<0.05) control of alfalfa compared to autumn application of glyphosate. Autumn disking and glyphosate application (Trts. 5 and 6) increased (P<0.05) rye biomass compared to no autumn treatment (Trts. 3 and 4). Applying glyphosate prior to corn planting (Trts. 3 and 4) improved (P<0.05) corn populations and growth compared to autumn glyphosate or disking (Trts. 5 and 6) and was similar to conventional no-till establishment (Trt. 1). Herbicides were necessary to completely kill alfalfa, but grazing reduced TNC in alfalfa roots and alfalfa plant persistence. / Master of Science

O esforço global em diversificar a matriz mundial de combustíveis líquidos, busca substituir as fontes fósseis por renováveis. A produção de bioenergia derivada da biomassa assume importante papel neste cenário. A biomassa gerada após a colheita da cana-de-açúcar ganha destaque como matéria prima pela grande quantidade de material que pode ser usado para geração direta (queima) e indireta (biocombustíveis) de bioenergia. No entanto, ainda pouco se sabe sobre os efeitos da remoção de quantidades de palha de cana-de-açúcar voltado à produção de bioenergia sobre os atributos biológicos do solo. Assim, o objetivo deste estudo foi avaliar o efeito da remoção da palha de cana-de-açúcar no carbono e nitrogênio microbiano e na comunidade microbiana do solo. O estudo foi conduzido em duas áreas cultivadas com cana-de-açúcar (Saccharum spp. L.) nos municípios de Capivari, SP (Usina Bom Retiro) e Valparaíso, SP (Usina Univalem). Em Bom Retiro o experimento foi instalado em um Latossolo Vermelho distrófico típico de textura franco-argilo-arenosa e, em Univalem foi um Argissolo Vermelho-Amarelo distrófico de textura arenosa. Em ambos locais, o delineamento experimental utilizado foi blocos casualizados, com cinco tratamentos e quatro repetições. Os tratamentos testados corresponderam a diferentes intensidades de remoção de palha de cana-de-açúcar (i.e., 100%; 75%; 50%; 0 de remoção; e aleiramento da quantidade remanescente na área após colheita), sendo 0; 3,4; 7,8; 16,6; 15,6 Mg ha-1 de palha em massa de matéria seca na Usina Bom Retiro e 0; 4,2; 8,7; 18,9; 23,3 Mg ha-1 na Usina Univalem. Um ano após a instalação do experimento, foram coletadas amostras de palha e de solo na camada 0-10 cm e, passados quatro meses após o segundo manejo de remoção da palha nos tratamentos foram coletadas amostras de palha e de solo nas camadas 0-5 e 5-10 cm. Os atributos avaliados foram: carbono e nitrogênio total da palha e do solo, fração mais oxidável do carbono do solo, carbono e nitrogênio da biomassa microbiana da palha e do solo e, quantificação de genes microbianos no solo. Os resultados mostraram que as quantidades de C e N totais no solo não apresentaram resposta em função das quantidades de palha, no entanto, a fração de C mais facilmente oxidável e o C e N microbiano apresentaram tendência de redução em função de maiores níveis de remoções de palha, sendo a resposta da biomassa microbiana mais expressiva no solo de textura arenosa (i.e., Univalem). Da mesma forma, as comunidades microbianas foram mais sensíveis às diferentes remoções de palha, apresentando maior abundância com menor remoção de palha. Desta forma, a remoção de elevadas quantidades da palha de cana-de-açúcar do campo, ao alterar a microbiologia do solo, pode ter consequências nas específicas funções exercidas por este compartimento, que garantem o bom funcionamento do solo e podem prevenir contra a degradação. Estes resultados podem servir de base para avaliações mais amplas que buscam uma estratégia sustentável de manejo da palha de cana-de-açúcar que garanta o bom funcionamento do solo / The global effort to diversify the global matrix of liquid fuels seeks to replace fossil sources by renewable ones. Bioenergy production derived from biomass plays an important role in this scenario. The biomass generated after the harvest of sugarcane stands out by the large amounts of straw that can be used for direct generation (burning) and indirect (biofuels) of bioenergy. However, little is know about the effects of sugarcane straw removal to bioenergy production on biological soil properties. The objective of this study was to evaluate the effect of the straw removal on soil microbial carbon and nitrogen as well as on soil microbial community. The experiments were conducted in two areas cultivated with sugarcane (Saccharum spp. L.) in Capivari, SP (Bom Retiro) and Valparaíso, SP (Univalem). The soils studied were an Oxisoil with clay texture in Bom Retiro and an Ultisoil with sandy texture in Univalem. In both sites, the experimental designer was a randomized blocks with five treatments and four replications. The treatments tested were decreasing intensities of sugarcane straw harvest (i.e., 100%; 75%; 50%; 0 removing of the original straw deposition) : i) Bom Retiro: 0; 3,4; 7,8; 16,6; 15,6 Mg ha-1 of dry matter of straw kept on soil surface; ii) Univalem: 0; 4,2; 8,7; 18,9; 23,3 Mg ha-1 of dry matter of straw kept on the soil surface. One year after experiment installation, straw and soil (0-10 cm layer) samples were collected. A new sugarcane straw and soil (0-5 and 5-10 cm) sampling was performed four months from the second deposition of sugarcane straw on the field. The attributes evaluated were: total and microbial C and N of straw and soil, soil easily-oxidizable C, straw and soil microbial genes quantification using qPCR method. Our results showed that soil C and N contents were not impacted by sugarcane straw removal. However, the fraction of easily-oxidizable C and microbial C and N tended to decrease due to increased straw removal, with a more significant microbial biomass response for the sandy soil site (Univalem). Likewise, microbial communities were also sensitive to straw management, resulting in a significant decrease in the number of gene copies with increasing intensities of sugarcane straw harvest. Therefore, we can concluded that the large amounts of sugarcane straw removal from field as affects soil microbiology, may have consequences in specific functions performed by microorganisms, which ensure the soil functioning and can prevent soil degradation. These results can serve as a basis for more comprehensive assessments that seek a sustainable crop residue management strategy for sugarcane, to ensure the proper functioning of the soil

O esforço global em diversificar a matriz mundial de combustíveis líquidos, busca substituir as fontes fósseis por renováveis. A produção de bioenergia derivada da biomassa assume importante papel neste cenário. A biomassa gerada após a colheita da cana-de-açúcar ganha destaque como matéria prima pela grande quantidade de material que pode ser usado para geração direta (queima) e indireta (biocombustíveis) de bioenergia. No entanto, ainda pouco se sabe sobre os efeitos da remoção de quantidades de palha de cana-de-açúcar voltado à produção de bioenergia sobre os atributos biológicos do solo. Assim, o objetivo deste estudo foi avaliar o efeito da remoção da palha de cana-de-açúcar no carbono e nitrogênio microbiano e na comunidade microbiana do solo. O estudo foi conduzido em duas áreas cultivadas com cana-de-açúcar (Saccharum spp. L.) nos municípios de Capivari, SP (Usina Bom Retiro) e Valparaíso, SP (Usina Univalem). Em Bom Retiro o experimento foi instalado em um Latossolo Vermelho distrófico típico de textura franco-argilo-arenosa e, em Univalem foi um Argissolo Vermelho-Amarelo distrófico de textura arenosa. Em ambos locais, o delineamento experimental utilizado foi blocos casualizados, com cinco tratamentos e quatro repetições. Os tratamentos testados corresponderam a diferentes intensidades de remoção de palha de cana-de-açúcar (i.e., 100%; 75%; 50%; 0 de remoção; e aleiramento da quantidade remanescente na área após colheita), sendo 0; 3,4; 7,8; 16,6; 15,6 Mg ha-1 de palha em massa de matéria seca na Usina Bom Retiro e 0; 4,2; 8,7; 18,9; 23,3 Mg ha-1 na Usina Univalem. Um ano após a instalação do experimento, foram coletadas amostras de palha e de solo na camada 0-10 cm e, passados quatro meses após o segundo manejo de remoção da palha nos tratamentos foram coletadas amostras de palha e de solo nas camadas 0-5 e 5-10 cm. Os atributos avaliados foram: carbono e nitrogênio total da palha e do solo, fração mais oxidável do carbono do solo, carbono e nitrogênio da biomassa microbiana da palha e do solo e, quantificação de genes microbianos no solo. Os resultados mostraram que as quantidades de C e N totais no solo não apresentaram resposta em função das quantidades de palha, no entanto, a fração de C mais facilmente oxidável e o C e N microbiano apresentaram tendência de redução em função de maiores níveis de remoções de palha, sendo a resposta da biomassa microbiana mais expressiva no solo de textura arenosa (i.e., Univalem). Da mesma forma, as comunidades microbianas foram mais sensíveis às diferentes remoções de palha, apresentando maior abundância com menor remoção de palha. Desta forma, a remoção de elevadas quantidades da palha de cana-de-açúcar do campo, ao alterar a microbiologia do solo, pode ter consequências nas específicas funções exercidas por este compartimento, que garantem o bom funcionamento do solo e podem prevenir contra a degradação. Estes resultados podem servir de base para avaliações mais amplas que buscam uma estratégia sustentável de manejo da palha de cana-de-açúcar que garanta o bom funcionamento do solo / The global effort to diversify the global matrix of liquid fuels seeks to replace fossil sources by renewable ones. Bioenergy production derived from biomass plays an important role in this scenario. The biomass generated after the harvest of sugarcane stands out by the large amounts of straw that can be used for direct generation (burning) and indirect (biofuels) of bioenergy. However, little is know about the effects of sugarcane straw removal to bioenergy production on biological soil properties. The objective of this study was to evaluate the effect of the straw removal on soil microbial carbon and nitrogen as well as on soil microbial community. The experiments were conducted in two areas cultivated with sugarcane (Saccharum spp. L.) in Capivari, SP (Bom Retiro) and Valparaíso, SP (Univalem). The soils studied were an Oxisoil with clay texture in Bom Retiro and an Ultisoil with sandy texture in Univalem. In both sites, the experimental designer was a randomized blocks with five treatments and four replications. The treatments tested were decreasing intensities of sugarcane straw harvest (i.e., 100%; 75%; 50%; 0 removing of the original straw deposition) : i) Bom Retiro: 0; 3,4; 7,8; 16,6; 15,6 Mg ha-1 of dry matter of straw kept on soil surface; ii) Univalem: 0; 4,2; 8,7; 18,9; 23,3 Mg ha-1 of dry matter of straw kept on the soil surface. One year after experiment installation, straw and soil (0-10 cm layer) samples were collected. A new sugarcane straw and soil (0-5 and 5-10 cm) sampling was performed four months from the second deposition of sugarcane straw on the field. The attributes evaluated were: total and microbial C and N of straw and soil, soil easily-oxidizable C, straw and soil microbial genes quantification using qPCR method. Our results showed that soil C and N contents were not impacted by sugarcane straw removal. However, the fraction of easily-oxidizable C and microbial C and N tended to decrease due to increased straw removal, with a more significant microbial biomass response for the sandy soil site (Univalem). Likewise, microbial communities were also sensitive to straw management, resulting in a significant decrease in the number of gene copies with increasing intensities of sugarcane straw harvest. Therefore, we can concluded that the large amounts of sugarcane straw removal from field as affects soil microbiology, may have consequences in specific functions performed by microorganisms, which ensure the soil functioning and can prevent soil degradation. These results can serve as a basis for more comprehensive assessments that seek a sustainable crop residue management strategy for sugarcane, to ensure the proper functioning of the soil

A two year study was initiated in 2001 on a 2.4 ha site of mostly St. Amable loamy sand and shallow loamy sand at the Macdonald Campus Research Farm. This study sought to assess the effects of long term tillage and residue practices on soil physical properties and to relate these properties to their influence on total carbon, total nitrogen and soil microbial biomass-carbon. The site was set up as a factorial experiment with three tillage practices (no till---NT; reduced till---RT; and conventional till---CT) and two residue practices (with residue (grain corn), +R; without residue (silage corn), -R). Soil physical properties measured were bulk density, macroporosity at -6 kPa, saturated hydraulic conductivity (Ksat ), dry aggregate distribution, soil moisture and soil temperature. Wheel versus non-wheel track bulk density was also determined in the NT plots. Total porosity, soil water characteristic curves and pore volume distribution were derived from field samples. Crop yield was also assessed. Tillage alone had an effect on total porosity, bulk density, pore diameter and macroporosity. No individual physical property was significantly affected by the residue treatments; however, the tillage and residue interaction was significant for Ksat, soil moisture and soil temperature. Dry aggregate distribution was not affected by either tillage, residue or the combination of the two. Tillage affected total carbon and total nitrogen in the 0--0.10 m depth. Soil microbial biomass-carbon was affected by residue inputs. Total carbon and nitrogen were influenced by the bulk density, but none of the other soil physical properties. Soil microbial biomass-carbon was not influenced by any of the physical properties. Tillage and residue practices had no significant effect on crop yield for either year.