Earthworms have an important role in the decomposition of organic matter, mineralization of nutrients and physical mixing of soils. Despite a large number of laboratory and greenhouse-level studies investigating how earthworms modify soil properties and promote soil fertility, we lack reliable methods to scale-up and quantify earthworm contributions to nutrient cycling at the agroecosystem level. The objective of this thesis is to determine the influence of earthworm communities on nitrogen (N) transformations in soils and to quantify their contribution to nitrogen flux through soils for soybean and maize cropping systems of Quebec. Laboratory growth rates were used to predict how earthworm growth responded to seasonal fluctuations in soil temperature and moisture. The relationships between earthworm populations, soil-N pools and annual crop production were evaluated in a field experiment. When favourable conditions occurred in 2004 (temperatures <20°C, and rainfall at least once a week), a positive relationship was found between earthworm numbers and the plant available-N, including soil mineral-N, microbial biomass-N and total-N removed in soybean grain. In 2005, soil conditions were unfavourable (temperatures > 20°C and little or no rainfall) to earthworm survival and growth, and no relationship was found between earthworm populations, soil N pools and corn production. These data permitted me to make assumptions about earthworm activity and life histories under field conditions, which were used to estimate N flux through earthworm communities with two models. The models were tested for their sensitivity to varying parameter values within the range reported in the scientific literature. During a crop growing period with favourable climate conditions, a large earthworm population (100 g fresh weight biomass m-2 or greater) is predicted to cycle as much as 120 kg N ha-1. Model predictions were very sensitive to input parameters and did not correspond to the partial N budget calculated at the site. Accurate predictions of N mineralization by earthworms require more species- and site-specific parameter values. Further investigation using stable 15N isotopes as tracers would help us to follow the N transformations and evaluate the N flux mediated by earthworms at the field scale.

Urea and triple superphosphate (TSP) are important N and P fertilizers, respectively, but they suffer from inefficiency because of NH$ sb3$ volatilization and phytotoxicity and P fixation. Combinations of urea and TSP or KCl might improve N and P use efficiency primarily through pH changes. Mixtures of urea, TSP and KCl, either compacted or blended, were studied as to NH$ sb3$ volatilization, denitrification and P transformation in soils, and N and P use efficiency in crops. Soils studied included a Ste. Rosalie clay (Humic Gleysol), an Ormstown silty clay loam (Humic Gleysol), a Chicot sandy clay loam (Grey Browm Luvisol), a St. Bernard loam (Melanic Brunisol) and an Upland loamy sand (Humo Ferric Podzol). Triple superphosphate or KCl reduced urease activity and delayed urea hydrolysis primarily through acidification. Ammonia volatilization decreased when urea was surface-applied with TSP or KCl. The depressive effect of TSP on NH$ sb3$ volatilization was reduced and the KCl effect was increased in the soil with high exchangeable acidity. Phytotoxicity from banded urea, NO$ sb2 sp-$ accumulation and denitrification declined with added TSP. Urea hydrolysis caused a rise in pH and dissolution of organic matter in soils, and as a result, Mehlich (3) and water extractable P increased when urea were banded with TSP. Corn yield and N and P use efficiency were improved with application of mixtures of TSP and urea as compared with urea or TSP alone. Compacted mixtures of urea and TSP or KCl were superior to blended mixtures, possible because of the intimate association of fertilizer dissolution products. Compacted mixtures of urea and TSP or KCl hold promise for improved agricultural productions.

The effects of added potassium, K, magnesium, Mg and sulfur, S on corn grain and silage yields were investigated in the field for two years. / Due to high nutrient soil, K, Mg and S had no effects on corn grain and silage yields. However, there were trends observed in the treatment effects that were significant. Added K at 240 kg K$ sb2$O/ha increased grain yield over zero kg K$ sb2$O/ha in 1983 and Mg at 60 kg/ha increased grain yield over 30 kg/ha in 1984. In silage, 240 kg K$ sb2$O/ha increased yield over 120 and zero kg K$ sb2$O/ha in 1984. Although there was no K by Mg interaction, there was a need for added Mg to achieve higher yields. / The cumulative effect of fertilizer S at 50 kg/ha significantly reduced silage yield in 1984 over zero S treatment indicating that fertilizer S was unnecessary for corn growth by reason of high levels of soil S and sufficient S provided from precipitation and air dry deposition. S had no interaction with K and Mg because there was no need for fertilizer S to increase yields. / The antagonistic association between K and Mg was seen at the seedling, tasseling and silking stages. / There was an indication of a K by S interaction which was expressed at different stages of growth, but this effect was not evident for dry matter yields.

Concern about NO$ sb3 sp-$-N leaching and groundwater pollution from monoculture corn (Zea mays L.) has prompted investigation of alternative production systems which reduce N leaching. Both intercrop systems and water table controls alone have been shown to increase nitrogen (N) uptake and reduce soil NO$ sb3 sp-$-N accumulation in cropping systems. There is a need to maintain crop productivity while reducing the potential for soil NO$ sb3 sp-$-N leaching into groundwater. However, there has been no information available regarding agronomic and physiological aspects of N and water management for monocrop corn and corn competing with annual Italian ryegrass (Lolium multiflorum Lam) in an intercrop system. A study was conducted in southwestern Quebec during 1993 and 1994. Nitrogen and dry matter components in the plant-soil system were determined. Intercropped corn grain yield did not differ from monocropped corn under high N fertility. At harvest, the corn-annual ryegrass intercrop system increased total aboveground N uptake by 77.2 and 50.7 kg ha$ sp{-1}$ when compared with the corn monocrop system in 1993 and 1994, respectively. The intercrop system reduced the amount of NO$ sb3 sp-$-N in the top 1 m of soil by 47% (92.3 kg N ha$ sp{-1}$) at harvest in 1993. Water table controls had little effect on corn yield, N use efficiency and soil NO$ sb3 sp-$-N accumulation over the two years of this study. Both plant establishment and weather conditions affected the ability of annual ryegrass to aid in the uptake of soil NO$ sb3 sp-$-N. The reproductive development of water stressed plants after silking was limited more by overall plant changes due to water stress than assimilate supply. The delivery of C (sucrose) and N ($ sp{15}$N urea) into corn plants via stem-injection showed that externally supplied C changed both the source strength (photosynthetic inhibition) and sink strength (decreased total grain production), while distribution of $ sp{15}$N was affected by p

Cover crops may be used as a management tool in modifying soil water content, helping lower agriculture’s impact on water quality and lead to greater crop yields. During the 2012 growing season, a field study was conducted in Albany, IN to determine: 1) the impact of cover crops on soil moisture throughout the growing season and 2) cover crops’ influence on corn (Zea mays) yield. Treatments of a monoculture of annual ryegrass (Lolium multiflorum) (AR), a mixture of annual ryegrass (Lolium multiflorum), crimson clover (Trifolium incarnatum), and groundhog radish (Raphanus sativus) (MIX), were compared with a no cover crop control (CTRL) in a randomized complete block design, with blocks positioned in moderately well drained (MWD) and poorly drained (PD) soils. Cover crop treatments were similar to each other in accelerating moisture removal before the corn growing season, resulting in soil profiles that were 47% drier in the MWD soil and 22% drier in the PD soil than controls. Abnormally hot and dry weather conditions made water availability a limiting factor and decreased the relative importance of soil nitrogen while corn was growing. In the MWD soils, corn grown after MIX treatments had 21% higher yields than CTRL treatments and 11% higher yields than AR treatments due to increased subsoil water usage. Corn grain yields in PD soils were related to surface moisture conservation, leading to 3-5% higher yields in MIX and AR treatments. Implications for improved field trafficability, reduced runoff and tile drainage flow, and enhanced water availability to crops are discussed. / Department of Natural Resources and Environmental Management

Anthropogenic greenhouse gas emissions are the main cause of increasing global temperatures. Climate change will affect crop production in Canada and, in turn agriculture has the potential to mitigate climate change. Analysis of historical climate and corn yield data, and field and greenhouse experiments were carried out in order to study the effect of climate variability and changes on corn yield, the adaptability of cropping systems to climate change conditions, the effect of tillage on soil greenhouse gas emissions (CO2 and N2O) associated with corn and soybean production, and the potential of Nod factors to increase biomass as way to mitigate CO2 emissions. In southwestern Quebec, corn yield variability has been strongly associated to July temperature and May precipitation during the last three decades. Field studies showed that switchgrass and sorghum-sudangrass were best adapted to dry and warm climate events. No-till improved corn yield when spring temperatures were warmer than normal. Soil CO2 fluxes were associated with temperature, while soil N2O fluxes were associated with precipitation. Conventional tillage (CT) had greater CO2 emissions than no-till (NT), particularly after disking in the spring. Both tillage systems had large N2O emission peaks during the wettest part of the season. In corn, peaks of N 2O occurred after nitrogen fertilizer application. NT had greater N 2O emissions than CT in the corn production systems; however, CT had greater N2O fluxes than NT in the soybean production system. Nod factors sprayed on soybean increased photosynthesis and biomass under controlled conditions. In the field, yield was increased by Nod factors under CT, but not under NT, and drought reduced the soybean response to Nod factors. / Les émissions anthropogènes de gaz à effet de serre sont la cause principale de l'augmentation globale des températures. Les changements climatiques vont affecter la production agricole au Canada, et en retour, l'agriculture pourrait limiter les changements climatiques. L'analyse de données historiques du climat et des rendements de maïs, combinés avec des expériences de serre et en champ ont été entreprises pour étudier l'effet de la variabilité et des changements de climat sur le rendement de maïs, l'adaptabilité des systèmes agricoles aux changements climatiques, l'effet du travail du sol sur les émissions de gaz à effet de serre (C02 et N20) associées avec la production de maïs et de soya, et le potentiel des facteurs Nod d'augmenter la biomasse pour limiter les émissions de CO2. L'analyse des données historiques ont démontré qu'au sud-ouest du Québec, la variabilité des rendements de maïs est fortement associée avec les températures de juillet et les précipitations de mai pendant les dernières trois décennies. Les expériences au champ ont démontré que le panic raide, et le sorghum-sudangrass sont les mieux adaptés aux conditions chaudes et sèches. Le semis direct a augmenté les rendements de maïs lorsque les températures printanières étaient plus chaudes que la normale. Les flux de C02 étaient associés avec la température, mais les flux de N20 étaient associés avec les précipitations. Le travail du sol conventionnel (CT) a produit plus d'émissions de CO2 que le semis direct (NT), particulièrement après le disquage au printemps. Les deuxsystèmes ont montré un large pic d'émission de N20 pendant les périodes les pluspluvieuses. Dans le maïs, les pics de N20 ont été détectés après la fertilisation enazote. NT a montré des émissions de N20 plus importantes que CT en productionde maïs, mais CT a montré des flux de N20 plus important que NT en productionde soya. Les facteurs Nod vaporisés sur le soya ont augmenté la photosynthèse etla biomasse sous conditions controllées. Au champ, le rendement a été augmentépar les facteurs Nod sous CT, mais pas sous NT, et la sécheresse a réduit laréponse du soya aux facteurs Nod.

The effect of management practices used by smallholder farmers to improve soil quality and increase maize yield was examined in an 80 ha. micro-watershed of central Malawi. Because of the complexity inherent in smallholder farming systems, this research proposed the combination of participatory methods with analytical techniques developed in field ecology, such as multivariate and spatial analysis. During a Participatory Rural Appraisal (PRA), farmers identified factors potentially influencing soil quality and maize yield. One hundred and seventy-six (176) plots were located in twenty-nine (29) fields and characterized for management practices and biophysical characteristics. Soil samples were collected at each plot and analysed for a suite of properties. The maize yield was measured for both 1996--97 and 1997--98 seasons. A formal survey was used to gather information on household characteristics. Results showed that management practices that were promoted by a previous extension project, such as alley cropping and the planting of grass on contour ridges, were strongly correlated and found mainly in fields located closer to house compounds. Farmers with a higher proportion of their land under wetland gardens tended to use less agroforestry. Food security was associated with households that were able to purchase inorganic fertilizers, had larger landholding size, and owned livestock and woodlots. The effect of management practices on maize yield and soil quality was partially confounded with characteristics of the plot, such as slope, degradation level, number of years under cultivation or pest damage. Higher maize yield was observed in plots that were better managed, as expressed by the combination of different management practices, lower pest incidence, fewer erosion signs and higher soil fertility. Some positive effects of alley cropping on soil quality were observed in plots that were cultivated for a longer period and located on flatter land. This study demo

The purpose of this study was to investigate the effect of maize (Zea mays L.) hybrids, plant population, rates of fertilization and irrigation in 1984 and 1985 on soil test levels, soil pH, yield and yield components as well as nutrient uptake. / High rates of fertilization increased soil test P and K but decreased soil test Ca and Mg and soil pH. Irrigation decreased soil test K, Ca and Mg. In both years maximum grain yields (at 15.5% moisture) were obtained when all factors were at high levels. Hybrid Pioneer 3925 and and hybrid CO-OP 2645 produced a maximum yield of 11.9 and 15.2 Mg ha$ sp{-1}$ in 1984 and 1985, respectively. Increasing plant population alone increased grain yield from 9.6 to 10.4 Mg ha$ sp{-1}$ in 1984, bu increases in grain yield with high plant population in 1985 could only be obtained when high rate of nutrients and supplemental irrigation were applied. / Nutrient uptake was usually greater for hybrid 2645 than hybrid 3925 in 1985, and greater for hybrid 3925 than for hybrid 3949 in 1984. Increasing plant population, rate of fertilization as well as available soil moisture generally brought about greater nutrient uptake. Ear leaf nutrient concentration at silking time was influenced by these factors but the differences obtained were not agronomically significant.

Thesis (M. A. Agriculture (Agricultural Economics)) -- University of Limpopo, 2021 / Maize seeds differ according to varieties.The traditional maize varieties(also referred to as (Landraces)are maize varieties that have been cultivated and subjected to selection by farmers for generations.They retain a distinct identity and lack formal crop improvement. Improved maize varieties,on the other hand,are bred with characteristics such as drought and disease tolerance. This research was conducted to determine the attributes preferred by farmers when making a maize varietal choice.To be specific, the study aimed to achieve the following objectives:(i) Identify and describe socio economic characteristics of smallholder maize farmers’ in Mogalakwena Municipality; (ii) Analyse socioeconomic characteristics of smallholder maize farmers in Mogalakwena Municipality; (iii) Identify different maize varieties grown by smallholder farmers in Mogalakwena Municipality,and (iv) determine and analyse factors influencing farmers’choice ofa maize variety. Descriptive statistics and the Multinomial Logistic Regression Model were used for data analysis.The results of the study revealed that 64% of the respondents had formal education.This meant that they have the capability to grasp more information, if provided with trainings. It was found that 75% of the farmers did not have access to extension service which is supposed to play a significant role in agricultural information dissemination.The most grown maize variety was land race varieties which constituted 59.5%. This percentage was said to be resultant from limited access to the seed market. Infact,80% of the farmers had to travel an average of 42 kilomteres to access the market which also had a limited number of varieties.The Multinomial Logistic Regression Model revealed that only 5 variables (Educational level, farm size, yield, extension contact and knowledge of maize varieties )were significantat1%,5%,1%,1% and1%, respectively.The majority of farmers were old people with little access to extension service and an inadequate farming knowledge which lead to a highper centage of farmers continuing to grow landrace varieties. Based on the findings, this study recommend further research on attributes that influence farmers varietal choice and Government intervention in provision for resources and development of existing and new infracstrcture to encourage extension service delivery. Keywords:Landrace,improvemaizevariety,smallholderfarmer

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