Contemporary row-crop practices in the mid-southern, USA contribute to declining water tables and impairment of downstream waters, threatening the sustainability of irrigated agriculture and vital ecosystem services. This research was conducted to determine if various conservation practices and technologies can economically reduce negative environmental consequences of regional corn (Zea mays L.) production. The environmental, agronomic, and economic effects of implementing cover crops, manipulating traffic pattern, and integrating irrigation water management (IWM) technologies (computerized hole selection, surge irrigation, and soil moisture sensors) were investigated at either the small plot or field scale in the Delta region of Mississippi. Cover crop effects on runoff, water quality, corn grain yield, and net returns were primarily neutral or negative. Under furrow irrigation, cover crops did not affect runoff or nitrogen and phosphorus transport, but decreased erosion 16%. No cover crop decreased rainfall-induced runoff, erosion, or N and P transport. Over the four years of the experiment, cover crops maintained or decreased yield, net returns, and water use efficiency. Eliminating equipment traffic from furrows largely maintained or reduced runoff and subsequent contaminant transport. For both furrow irrigation and simulated rainfall, runoff and erosion were consistently less from nontraffic furrows than traffic furrows. Traffic effects on nutrient transport was more variable. Transport of some phosphorus constituents was decreased in the absence of furrow traffic; however, rainfall-induced nitrogen transport was greater from nontraffic furrows during the late-season event. Irrigation water management technologies improved corn grain yield, net returns, and irrigation water use efficiency across multiple locations in the mid-southern USA. Relative to standard production practices, implementing IWM technologies reduced total water applied 40% and increased corn grain yield 6.5 bu acre-1, which constituted a 51% increase in irrigation water use efficiency. The decrease in cost for irrigation water applied and increase in returns from yield gains exceeded the cost of the IWM technologies and resulted in an increase in net returns across a range of pumping depth and diesel price scenarios. Of the evaluated conservation strategies, reducing equipment traffic and implementing IWM technologies will most consistently improve the sustainability of irrigated agriculture and ecosystem services in the mid-southern USA.

Improved N management is required to enhance crop productivity, while reducing concomitant losses. Research was conducted for 4-y studying winter cover crops. Three legume species grown alone or with either cereal rye (Secale cereale) or ‘Tillage Radish®’ (Raphanus sativus L.) were used to quantify cover crop biomass and N content plus their effects on corn grain yield and N recovery. The effects of these cropping systems on selected soil health indicators was also determined. Rye bicultures enhanced biomass production, but antagonistically affected corn performance. Radish inclusion resulted in equal or greater cover crop N than rye. In year 3, the addition of radish across legume species increased corn N content (10.6 kg ha-1) and grain yield (1050 kg ha-1). Although cover crops did not affect soil bulk density, both bicultures increased soil C/N. The legume-radish association offers a novel practice towards improving crop performance and soil quality.

La alta frecuencia de cultivos de oleaginosas con moderados aportes y persistencia de residuos podría limitar la normal productividad de los suelos. La inclusión de cultivos invernales (utilizados como cultivos de cobertura, CC) en la región semiárida y subhúmeda pampeana sería una alternativa para proveer de residuos ricos en C y promover al desarrollo y al mantenimiento de la cobertura de los suelos. Pero se reconoce que el consumo hídrico de éstos podría interferir en la oferta de agua para el cultivo siguiente. El objetivo de este estudio fue evaluar la eficiencia en la producción de materia seca (MS) de cereales de invierno utilizados como CC y sus efectos sobre los contenidos de agua útil y nitratos en suelos diferenciados por el régimen hídrico. Los estudios se desarrolla-ron en 4 sitios experimentales [Luan Toro (LP) (Haplustol Entico, precipitación 624 mm), Dorila (LP) (Haplustol Entico, precipitación 873 mm), General Villegas (BA) (Hapludol Thapto Árgico, precipitación 906 mm) y General Pinto (BA) (Argiudol Típico, precipitación 1116 mm)]. Los tratamientos fueron: Secale cereale (C), Lolium multiflorum (R), Avena sativa (A) y un tratamiento Testigo, sin CC (T). La producción de MS al momento del secado de los CC varió entre 1226 y 10500 kg ha-1. Se observó una gran influencia del régimen hídrico de los suelos sobre la producción del MS de los CC. El contenido de agua total al momento de la siembra explicó el 57 % de la variabilidad de la producción de MS, mientras que el contenido de agua total en el suelo a la siembra más las precipitaciones durante el ciclo de desarrollo de los CC, explicó el 89 % de la variabilidad. En todos los sitios el centeno produjo la mayor cantidad de MS, seguida por la avena y el rye grass. La mayor variación se dio dentro del mismo sitio, entre los años de evaluación. El uso consuntivo hasta el momento del secado varió entre 88 y 299 mm. La especie con mayor eficiencia de uso de agua fue el centeno, alcanzando su máximo valor en el sitio de General Pinto (54 kg MS mm-1). Los valores de resistencia a la penetración fueron mayores bajo los tratamientos con CC y tuvieron una relación significativa con los contenidos hídricos del suelo. Sólo en el sitio Dorila los mayores valores fueron registrados en el tratamiento T, sin comprobarse relación significativa entre variaciones en la RP y los contenidos hídricos del suelo. Los contenidos de N-NO3- en el suelo fueron mayores en los tratamientos testigos, independientemente del sitio, en tanto que los contenidos de N de la biomasa variaron entre 29 y 275 kg ha-1; con mayores valores para el centeno. La producción de soja varió entre 1069 y 5346 kg ha-1 y no se afectó por la inclusión de CC. Estudios futuros deben, en el largo plazo, contemplar el beneficio de la incorporación de CC sobre las propiedades físicas y químicas del suelo en sistemas agrícolas de la región semiárida y subhúmeda pampeana dedicados al cultivo de soja. / The soil productivity can be limited because of a frequent presence of oil crops and because of their little residue cover production and persistence on the soils. In the semiarid and subhumid Pampas region, the use of winter cover crops (CC) could provide residues with high C contents and maintain an adequate soil residue cover. But, the soil water use of the CC during the winter season can modify the normal soil water availability for the follo-wing crop. The objective of this research was to evaluate the dry matter (MS) production efficiency of winter cereals cultivated as CC and their effect on the soil available water and soil nitrates under two soil moisture regimes. The study was performed in four experimental sites: Luan Toro (La Pampa) (Entic Haplustoll, mean anual rainfall of 624 mm), Dorila (La Pampa) (Entic Haplustoll, mean anual rainfall of 873 mm), General Villegas (Buenos Aires) (Thapto-argic Hapludoll, mean anual rainfall of 906 mm)and General Pinto (Buenos Aires) (Typic Argiudoll, mean anual rainfall of 1116 mm). The treatments were: Rye [Secale cereale (C)], Rye grass [Lolium multiflorum (R)] and oat [Avena sativa (A)] and an untreated control without CC (T). The MS production at the moment of killing the CC varied between 1226 and 10500 kg ha-1. A strong effect of the soil water regime on the MS production of the CC was observed. The soil water content at the moment of seeding the CC explained 57 % of the MS production and the soil water content at seeding and rainfalls during the CC growing season explained almost 89 % of the variability in MS production. In the four locations, rye showed the greater MS production followed by oat and rye grass. The greater variability was observed within each of the sites and the studied seasons. The water uptake at the moment of killing the CC varied between 88 and 299 mm. Rye was the cereal with greater water use efficiency with a highest value in General Pinto with 54 kg of MS mm-1. The soil penetration resistance (RP) values were higher under CC treatments and negatively related with the soil mois-ture contents. Only in Dorila the highest values of RP were observed in the control treatment without a significant relationship between them and the soil water contents. The soil N-NO3- contents were greater in the T than in the CC treatments. The N content of the CC biomass varied between 29 and 75 kg ha-1 achieving greater values with rye. The soybean grain production varied between 1069 and 5346 kg ha-1 without differences due to the CC treatments. Future studies should study the effects of the CC use of physical and chemical soil properties in agricultural systems from the semiarid and subhumid pampas region under continuous soybean crop production.

The purpose of this research carried out in 1998 and 1999 was to develop methods for strip cropping of cucumbers with rye/vetch and black plastic mulch. Effects of planting methods, weed control measures, and cover crop management techniques on pest and beneficial insects, petiole sap nitrate-nitrogen, soil moisture, yields and economic viability were assessed. Four treatments, namely cucumber direct seeded in black plastic mulch on tilled bare ground (conventional); cucumber direct seeded in black plastic mulch laid over incorporated rye/vetch residue; cucumber direct seeded into no-till rolled rye/vetch; and seedlings transplanted into no- till rolled rye/vetch, were evaluated in a randomized complete block design. Weeds were controlled in half the plot by critical manual weeding and pre-emergence herbicides applied in the other half in all treatments except the conventional system. Three-week interval staggered plantings of buckwheat to provide flowers for adult beneficial insects were also evaluated. Results obtained indicate that rye/vetch habitat is more attractive to beneficial insects than cucumber beetles before rolling or flail mowing. There were higher densities of adult Diptera (an indicator for Tachinid parasitoids) in both years and of Pennsylvania leatherwings in 1999 in plots with rye/vetch than in plots with rye only before planting. Preferential attraction to adult Diptera was not found after planting with no differences in cumulative densities between no-till and black plastic mulch plots after rolling or flail mowing. However, adult Diptera densities were positively correlated with cucumber yield, higher densities of cucumber beetles occurred in black plastic mulch than in no-till plots in both years, and bacterial wilt, transmitted by cucumber beetles, was reduced in no-till in 1999. Similarly, rye/vetch habitat plots had a higher diversity of Carabidae species (in both habitat areas and crop rows) before rolling or flail mowing, and higher densities of Carabidae (in habitat areas), Staphylinidae (in both habitat areas and crop rows) and spiders (in crop rows) after rolling or flail mowing. Black plastic mulch plots with flail mowed, incorporated rye/vetch residues had higher petiole sap nitrate-nitrogen and higher early season cucumber plant dry weights than in conventional plots; later in the season, the highest petiole sap nitrate-nitrogen occurred in no-till plots. No-till had higher marketable cucumber yield than plastic systems. The profitability of these production systems depended more on differences in marketable yield than on cost differences. The plastic with incorporated rye/vetch and no-till transplant systems were more profitable during early harvests in late July, while no- till direct seeded and transplant systems were more profitable from early August onwards. The three-week interval staggered planting of buckwheat led to conservation of beneficial insects, and the second and third seeded buckwheat flowering periods coincided with the period vetch had lost flowers. / Ph. D.

Field experiments were conducted in 1983 and 1984 to compare conventional tillage (CT) versus no-tillage (NT) production of broccoli and cabbage. The tillage treatments were applied in combination with four rates of applied nitrogen fertilizer and three cover crops: hairy vetch (<u>Vigia villosa</u> Roth), Austrian winter pea (<u>Fisum arvenu</u> L.), and cereal rye (<u>Secale cereale</u> L.). Transplants of 'Premium Crop' broccoli (<u>Brassica oleracea</u> var. <u>italica</u> Plenck) and 'Market Prize' cabbage (<u>Brassica oleracea</u> var. <u>capitata</u> L.) were set with a locally adapted NT vegetable planter. None of the variables studied affected the final plant stand. Yield and head size with NT were equal to or greater than CT. Soil moisture was higher under NT plots throughout the growing season. Yield and head size with the two legume covers were equal to or greater than those with the rye cover. Yield and head size tended to increase as applied N was increased, although differences were not always significant. The data, although not conclusive, indicate that the legume cover crops provided additional nitrogen for the cole crops. / Master of Science

The use of agrochemicals, like neonicotinoid insecticides can threaten human and environmental health when they are transported from agricultural fields. To minimize environmental impact of neonicotinoid pesticides to non-target organisms, it is important to quantify the movement of neonicotinoids from agricultural fields and examine how conventional agricultural practices can be altered using best management practices to minimize neonicotinoid transport. We developed a proportional runoff sampler that is inexpensive, rugged, and adaptable to existing runoff quantification systems. The sampler accurately collected flow-weighted samples under a broad range of steady-state and variable flow conditions. We then incorporated the sampler, along with leachate and soil sampling techniques, in a two-year field study testing the effects of winter cover crops and different edge-of-field buffer strip plant types on movement of the neonicotinoid thiamethoxam (TMX) and its metabolite clothianidin (CLO) in treated agricultural fields. Due to dry weather and other complications, runoff and leachate data could not be statistically analyzed. Soil samples indicated that cover crops had no effect on insecticide retention, so cover crops may not be a viable strategy to prevent neonicotinoid transport. Soil TMX was higher in grass buffers than native forb buffers in 2020; however, this result was not repeated in 2021 when vegetative cover was more consistent across treatments. CLO concentration did not vary by buffer in either year. Therefore, buffer strip plant type may have less impact on TMX and CLO retention than other factors like plant density. / Master of Science / Since the 1950's high yield crops and the use of pesticides and fertilizers have helped farmers increase yields from agricultural land. Increased yields have helped food production keep pace with population growth, but the use of pesticides and fertilizers can pose a threat to human and environmental health. Neonicotinoid insecticides can kill not only agricultural pests but beneficial invertebrates like bees and butterflies when the pesticides leave agricultural fields. To lessen environmental impact of neonicotinoid pesticides to the environment, it is important to understand 1) how these insecticides move from agricultural fields, and 2) how conventional agricultural practices can be altered to minimize neonicotinoid transport. We first developed a runoff sampler that was inexpensive, low maintenance, and adaptable to existing systems used to measure runoff. The sampler collects water at a rate proportional to the runoff rate under constant and changing flow rates. We then used the sampler along with leachate and soil sampling techniques in a field study testing the effect of winter cover crops and the species planted in edge-of-field vegetated buffer strips on the amount of the neonicotinoid thiamethoxam (TMX) and its degradation product clothianidin (CLO) remaining in the soil of treated fields during two growing seasons. Due to dry weather and other complications, runoff and leachate data could not be statistically analyzed. Cover crops did not change soil pesticide concentration either year, so cover crops may not be a viable strategy for preventing neonicotinoid transport. Soil TMX was higher in grass buffers than native forb buffers in 2020; however, this result was not detected in 2021 when plant growth in buffers was more uniform across treatments. CLO concentration did not vary by buffer type in either year. Therefore, the species planted in buffer strips may not be as important to holding TMX and CLO in soils as other factors like plant density.

Mid-Atlantic crop producers are increasingly transitioning to soil conservation methods that include reducing or eliminating tillage and planting high residue cover crops. These practices are associated with an increase in moderate to severe damage to field crops by slugs. Conserving, and even enhancing, natural enemy populations is a desirable way to manage slug infestations because remedial control measures are limited. To better understand how cover crop usage and tillage practices affect slug and natural enemy populations, 43 Virginia fields with different combinations of tillage practices and cover crop use were intensively sampled in 2018 and 2019. Fields were sampled over a six-week period during the early planting season when slugs are most problematic. Shingle traps and pitfall traps were used to sample slugs and natural enemies, respectively. To determine how multiple farming practices, soil composition, landscape features, and field history affect slug feeding injury to seedling plants, over 1,000 hectares of commercial production fields in the Shenandoah Region of Virginia were scouted for slug feeding injury to seedling plants. Corresponding crop producers were then surveyed on management methods. Our goal was to determine if slug feeding risk could be predicted by a single factor and or a combination of factors. Behavioral assays were performed with a common slug pest, Deroceras laeve, to determine if this species prefers feeding on maize, soybean, daikon radish, crimson clover, rye, or hairy vetch leaf tissue. Our sampling study found that cover crop use and conservation tillage type did not affect slug presence and damage, but that these factors affected various slug predators in different ways. We also observed that fields with more Phalangiidae and total predators overall had fewer slugs. Average slug feeding injury in both years was low and no factor or interaction of factors in our broader survey affected slug feeding injury ratings in fields. Behavioral assays indicated that slugs fed more on soybean tissue compared with maize, slugs consumed less maize when it was offered with hairy vetch or crimson clover, and slugs consumed less soybean when it was offered with hairy vetch or daikon radish. / Master of Science in Life Sciences / Invasive slug species the gray field slug, Deroceras reticulatum (Muller), and the marsh slug, Deroceras laeve, are major pests of maize and soybean grown in Virginia no-till systems. Slug feeding causes injury to young plants that, when severe, can reduce crop yield and necessitate replanting a field. Chemical control options are limited, and farmers may not be willing to use tillage as a control measure. Conserving arthropod slug predators may suppress pest populations below economic levels. Research is needed to understand how farming methods such as tillage type (e.g., no-till, strip tillage, vertical tillage) and cover crop use affect slugs and their predators. Our study investigated 1) how tillage type and cover crop use affected slug and slug predators, 2) if certain farming practices and field characteristics can be used to predict slug injury, and 3) if slugs preferred feeding on commonly-used cover crop species when offered with maize or soybean seedlings. Commercial production fields with different combinations of no tillage or reduced tillage, and planted with or without cover crops, were sampled to evaluate how these farming practices affect slugs and slug predators. Shingle traps and frames were used before planting and during early plant growth stages to collect and identify slug species; pitfall traps were used throughout the growing season to collect and identify slug predator species. To determine if slug feeding risk could be predicted, a survey of commercial production fields in the Shenandoah area was conducted and used to identify factors, if any, that influence slug feeding. Laboratory assays were used to determine feeding preference by offering slugs opportunity to feed on leaf tissue from a maize or soybean seedling or a mature cover crop species. We found that tillage type and use of cover crops did not affect the abundance of slugs, but that they did influence predator populations. The highest number of total predators were found in fields with reduced tillage, cover crops, and no insecticide use prior to crop emergence. Harvestmen were potentially the most impactful slug predator in the region. Field surveys suggested that no tested factor or interaction of factors affected slug injury to plants in commercial fields. Finally, we observed that slugs fed differently on soybean and maize tissue depending on cover crop species present.

Supply and synchronization of plant-available nitrogen (N) to the soil is a major challenge for organic farmers, especially when growing crops in soils that are in transition from conventional to organic systems. This research evaluated the effects of site produced cover crops and application of soil amendments on N uptake and crop yield of organic Irish potato (Solanum tuberosum) and sweet corn (Zea mays). Cover crops were crimson clover (Trifolium incarnatum) and forage radish (Raphanus sativus). Soil amendments included in-row application of commercially produced dehydrated compost tea absorbed on charcoal (Soil Biology Innovations) and post-plant sidedressing with organic N fertilizer. Irish potato and sweet corn were grown at the Kentland Agricultural Research Farm near Blacksburg, VA in an organic transition soil during the summers of 2006 and 2007. Nitrogen uptake and crop yield were not affected by cover crop species in either year. SBI increased yield of sweet corn, but not Irish potato for both years; SBI had no effect on N uptake of either crop. Post-plant N sidedressing increased N uptake and crop yield of Irish potato and sweet corn in 2007, but had no effect on crop yield in 2006, presumably because pre-plant organic fertilizer was applied at planting in 2006, but not in 2007. This study shows that the combination of site produced cover crops and applied soil amendments may be required to produce high marketable yields of organic Irish potato and sweet corn in the transition soil used in these experiments. / Master of Science

L'adozione di (agro)ecosistemi sostenibili viene indicata come una efficace strategia in grado sequestrare carbonio (C) nel suolo, mitigando così il cambiamento climatico e migliorando la fertilità. Sebbene il potenziale di sequestro del C della non-lavorazione (NT) sia stato generalmente sovrastimato, esso risulta essere di 0,26 Mg ha-1 anno-1 superiore rispetto al regime arativo. Inoltre, il 76,6% di questo quota è localizzato in frazioni considerabili come relativamente stabili. Il NT aumenta lo sviluppo radicale delle colture erbacee (es. mais, soia, frumento) negli stati superficiali del suolo (0-5 cm). Le correlazioni tra i parametri di densità radicale e le proprietà fisiche del suolo mostrano come lo sviluppo radicale sia un fondamentale indicatore di qualità del suolo in NT. I residui delle cover crops influenzano le emissioni di protossido d’azoto (N2O) in NT: i residui di segale favoriscono l'immobilizzazione dell’azoto (N), aumentandone così l'efficienza d’utilizzo e diminuendo le emissioni, mentre i residui di veccia vellutata aumentano l’N2O come conseguenza della mineralizzazione dell’N. Le emissioni di N2O e la produttività dei prati stabili possono essere positivamente correlate, perché meccanismi diversi rispetto alla regolazione indotta dalla disponibilità di N possono controllare l'N2O: il C potrebbe essere un principale fattore di regolazione per nitrificazione e denitrificazione. / Adoption of sustainable (agro)ecosystems has been widely suggested to increase soil organic carbon (C) sequestration, to mitigate climate change and enhance soil fertility. Although its carbon sequestration potential has been generally overestimated, no-till (NT) results in an extra C sequestration of 0.26 ± 0.18 Mg ha-1 yr-1 as compared to conventional tillage and 76.6% of this extra C is located in C pools which could be considered relatively stable. NT increases root development of field crops (i.e. maize, soybean, winter wheat) in the top soil (0-5 cm), while does not in the deeper soil (5-60 cm). Positive correlations between root density and soil physical parameters shows how roots are main drivers of soil physical properties under NT. Cover crop residues may affect nitrous oxide (N2O) emissions under NT: rye residues enhances soil-nitrogen (N) immobilization, thus increasing N use efficiency and decreasing N2O, while hairy vetch residues as cover crop under NT increases N2O as a consequence of soil-N mineralization. N2O emissions and shoot productivity may be positive correlated in grasslands, because other mechanisms than plant-induced regulation of soil N pool may control N2O: C could be a major factor regulating nitrification and denitrification processes.

Cette thèse visait à caractériser et à modéliser la dynamique des trois ressources principales que sont l'eau, l'azote et le rayonnement dans une association en relais maïs-plante de couverture en semis direct en région tropicale subhumide et ses conséquences sur la productivité de la culture principale et de l'ensemble du système et sur les flux d'eau et d'azote dans le sol. Le travail repose sur un dispositif expérimental mis en place dans les Cerrados, à Unaí (Minas Géras, Brésil) en 2007 pour deux années agricoles, d'une part en station expérimentale permettant un effort de mesure intense et d'autre part dans un réseau de parcelles d'agriculteurs offrant une large gamme de situations pédoclimatiques et de modalités de mise en œuvre des systèmes de culture étudiés. Dans ces derniers, la culture principale était un maïs, et la plante de couverture associée en relais était une culture fourragère tropicale, soit la légumineuse, Cajanus cajan soit la poacée, Brachiaria ruziziensis. Deux dates de semis, précoce et tardive étaient considérées pour le semis de la plante de couverture au sein du maïs, dans le cas de l'essai en station. Ce travail montre que rendement du maïs n'a pas été significativement affecté par la présence de la plante de couverture semée précocement au sein du maïs, en comparaison avec le rendement du maïs en culture pure. En revanche, la production en biomasse de la plante de couverture a été significativement réduite dans l'association. Le semis précoce de la plante de couverture au sein du maïs permet une production en biomasse significativement plus importante qu'un semis tardif (20 jours après floraison du maïs), et une production totale en biomasse de l'ensemble de l'association significativement plus importante par rapport aux cultures pures. Cette production totale a été plus du double comparée à celle de la culture pure de maïs dans le cas de l'association maïs-Cajanus. Les valeurs du Land Equivalent Ratio (LER) du rendement en grain de maïs et de la production de biomasse ont été supérieures à 1, atteignant jusqu'à 2.03 témoignant d'une meilleure valorisation des ressources par les espèces associées et l'avantage de tels systèmes pour produire à la fois du grain et du fourrage. La thèse montre aussi la forte variabilité du potentiel de production de ces systèmes en parcelles de producteurs et suggère que lorsque les ressources en eau et en azote sont moins disponibles que dans l'essai de station, des compétitions entre maïs et plantes de couverture peuvent réduire les performances agronomiques du maïs et/ou de la plante de couverture comparativement par rapport à la culture pure équivalente. La biomasse totale produite reste cependant supérieure à celle de la culture pure de maïs, sauf pour de rares exceptions où de plus faibles disponibilités en ressources, parfois accentué par des difficultés de gestion technique, le maïs semble souffrir de compétition plus forte et/ou la plante de couverture ne produit que très peu de biomasse. La thèse évalue la capacité d'un modèle de simulation de culture associées, STICS-CA, à fournir une analyse plus fine de la dynamique du partage des ressources dans ces systèmes et à en estimer les performances agronomiques et certains impacts environnementaux en fonction de conditions techniques et édapho-climatiques différentes de celles de notre dispositif. Des modifications mineures et le calage du modèle ont conduit à une simulation satisfaisante des cultures pures de maïs et Brachiaria et de l'association maïs-Brachiaria en semis direct sur mulch pailleux. En revanche il n'a pas été possible d'obtenir une simulation satisfaisante du maïs en semis conventionnel sur sol labouré, ni du Cajanus en culture pure et de l'association maïs-Cajanus en semis direct. . La thèse fournit des informations sur les imperfections du modèle et propose des améliorations aussi bien en termes de formalismes pour la prise en compte de la minéralisation du mulch, qu'en termes de dispo exp / This thesis dealt with characterizing and modeling the dynamics of the three principal resources which are water, nitrogen and radiation in a no-tillage relay intercropping maize-cover crop systems, under sub-humid tropical area climate. Moreover, productivity of the main crop and of the whole system and nitrogen and water flows in the soil are assessed.The study was based on an on-field approach/experimental design carried out during two crop growing seasons in Cerrados region, in Unaí (Minas Géras, Brazil) since 2007. Firstly, an experimental station was used allowing an intense effort of measurement and secondly, a whole of several farmer's fields offering a wide range of soil and climate conditions and modalities of implementation of the studied cropping systems. In the latter, main crop was maize, and intercropped cover crop was a tropical fodder crop, either leguminous, Cajanus cajan or gramineous, Brachiaria ruziziensis. Two dates of sowing, early and late were considered for the sowing of the cover crop in established maize, in the case of the experimental station. This study showed that maize yield was not significantly affected by the presence of the relay cover crops in comparison with maize as the sole crop, even when the cover crop was sown soon after maize emergence in comparison with maize sole crop. In contrast, the production of biomass by the cover crop was significantly lower when grown with maize than when it was grown as a sole crop. In the intercropped systems, when sown early, the cover crop produced higher total biomass than when sown late (20 days after maize flowering). Moreover, total aboveground biomass production of maize intercropped with a cover crop was much higher than that of any of the crops sown alone. Total biomass produced by maize and pigeon pea (Cajanus cajan) was more than double that maize grown alone. The Land Equivalent Ratio (LER) values of both maize grain yield and biomass production were higher than one, whatever the intercrop system, reaching up to 2.03 providing better available resources use efficiency by the intercropped plants. Thus, such systems permit to produce both maize grains and forage.The thesis shows also the strong variability of the production potential of these systems in farmer's fields and suggests that when water and nitrogen resources are less available than in the experimental station, competitions between maize and cover crops can reduce the agronomic performances of maize and/or the cover crop when compared to the equivalent pure sole crop. Total biomass produced by intercropping remained however higher than that of maize sole crop, except for rare exceptions where lower resources availability, sometimes accentuated by difficulties of technical practice, maize seems to suffer from stronger competition and/or the cover crop produced only very little biomass. The thesis evaluates the capacity of the STICS intercrop model, STICS-CA, to provide a finer analysis of the dynamics of the resource sharing in these systems and to estimate their agronomic performances and certain environmental impacts according to technical practices and soil and climate conditions that were different from those of our experimental station. Minor modifications and model calibration led to obtain satisfying simulations of the sole crops maize and Brachiaria and intercrop maize-Brachiaria in no-tillage under mulch. On the other hand, it was not possible to obtain satisfying simulations of sole crop maize in conventional tillage, nor of sole crop pigeon pea and intercrop maize-pigeon pea in no-tillage under mulch. The thesis provides information on the model imperfections and as well proposes improvements in terms of formalisms to take into account the mineralization of the mulch, as in terms of experimental design.