Agricultural economists have long studied crop yields and risk to help farm-level risk management. Producers face difficult decisions every year regarding market prices, management practices, and the uncertainty of weather. In our research, we use crop yield records while incorporating the modern portfolio theory to find the optimal planting portfolios giving a specific risk level. Our assets are on corn, cotton, and soybeans yields from the Mississippi Delta region. This study is unique because there are not any previous studies using crop histories linked to the modern portfolio theory. The main idea is to realize how much of each asset or what percentage to invest in out of the specific portfolio. By having these portfolios readily available for farmers, we aim to diminish the risk to help producers with springtime decision-making. Armed with these findings, we can better understand the economic implications of how crop rotations factor into farm-level risk management.

Differences in cropping practices, including tillage, inputs and crop rotations are the driving factors affecting weed dynamics (weed abundance, composition and crop-weed competition), which can ultimately affect crop yields. Several experiments were carried out to assess the impact of long-term organic and conventional cropping systems on weed abundance, weed community composition, crop yield and yield loss using a long-term (18 year) alternative cropping systems study (ACS) at Scott, Saskatchewan, Canada. The ACS study consisted of three input systems, namely high (conventional tillage), reduced (no-till conventional) and organic input systems and three crop rotation diversities (low diversity, diversified annual grains and diversified annual-perennials). A statistical analysis of the 18-year rotation revealed that the organic rotations have four and seven times higher weed density and 32% and 35% lower crop yields than the reduced and the high input systems respectively. Weed community composition was consistently different in organic rotations compared to the two conventional rotations throughout the years, but year to year random variations were more profound. All cropping systems showed an increase in weed density, weed biomass and crop yields over time, probably due to an increase in rainfall over time. Increasing the crop rotation diversity with annual and perennial crops did not reduce weeds, but decreased crop yields in all systems. A two-year micro-plot experiment with four additional weed competition treatments on the ACS study revealed that the wheat yields were lower in the organic rotations even in the absence of weeds, implying that lower crop yields were due to soil fertility related factors. A greenhouse pot experiment from soils obtained from both organic and reduced rotations revealed that wheat yields were still lower in organic compared to the reduced input systems, even after excess mineral N and P were added. Furthermore, no differences in crop yield loss due to weed competition among cropping systems were identified. Overall, this study revealed that eliminating tillage and reducing inputs are possible without long-term changes in weed abundance, weed community composition or affecting crop yields. However, eliminating synthetic inputs as was done in the form of organic crop rotations resulted in increased weed abundance, changed community composition and decreased crop yields.

In the semi - arid Mediterranean - type environments of southern Australia, soil and water resources largely determine crop productivity and ultimately the sustainability of farming systems within the region. The development of sustainable farming systems is a constantly evolving process, of which cropping sequences ( rotations ) are an essential component. This thesis focused on two important soil resources, soil water and nitrogen, and studied the effects of different crop sequences on the dynamic of these resources within current farming systems practiced on the upper Eyre Peninsula of South Australia. The hypothesis tested was that : continuous cropping may alter N dynamics but will not necessarily alter water use efficiency in semi - arid Mediterranean - type environments. Continuous cropping altered N - dynamics ; increases in inorganic N were dependent on the inclusion of a legume in the cropping sequence. Associated with the increase in inorganic N supply was a decrease in WUE by the subsequent wheat crop. Overall, estimates of water use efficiency, a common index of the sustainability of farming systems, in this study concur with reported values for the semi - arid Murray - Mallee region of southern Australia and other semi - arid environments worldwide. Soil water balance and determination of WUE for a series of crop sequences in this thesis suggests that the adoption of continuous cropping may increase WUE and confer a yield benefit compared to crop sequences including a legume component in this environment. No differences in total water use ( ET ) at anthesis or maturity were measured for wheat regardless of the previous crop. Soil evaporation ( E [subscript s] ) was significantly affected by crop canopy development, measured as LAI from tillering until anthesis in 2002, however total seasonal E [subscript s] did not differ between crop sequences. Indeed in environments with infrequent rainfall, such as the upper Eyre Peninsula, soil evaporation may be water - limited rather than energy limited and the potential benefits from greater LAI and reduced E [subscript s] are less. Greater shoot dry matter production and LAI due to an enhanced inorganic N supply for wheat after legumes, and to a lesser degree wheat after canola, relative to continuous cereal crop sequences resulted in increases in WUE calculated at anthesis, as reported by others. Nonetheless the increase in WUE was not sustained due to limitations on available soil water capacity caused by soil physical and chemical constraints. Access to more soil water at depth ( > 0.8m ) through additional root growth was unavailable due to soil chemical limitations. More importantly, the amount of plant available water within the ' effective rooting depth ' ( 0 - 0.8m ) was significantly reduced when soil physical factors were accounted for using the integral water capacity ( IWC ) concept. The difference between the magnitude of the plant available water capacity and the integral water capacity was approximately 90mm within the ' effective rooting depth ' when measured at field capacity, suggesting that the ability of the soil to store water and buffer against periodic water deficit was severely limited. The IWC concept offers a method of evaluating the physical quality of soils and the limitations that these physical properties, viz. aeration, soil strength and hydraulic conductivity, impose on the water supply capacity of the soil. The inability of the soil to maintain a constant supply of water to satisfy maximal transpiration efficiency combined with large amounts of N resulted in ' haying off ', and reduced grain yields. A strong negative linear relationship was established between WUE of grain production by wheat and increasing soil NO [subscript 3] - N at sowing in 2000 and 2002, which conflicts with results from experiments in semi - arid Mediterranean climates in other regions of the world where applications of N increased water use efficiency of grain. Estimates of proportional dependence on N [subscript 2] fixation ( % N [subscript dfa] ) for annual medics and vetch from this study ( 43 - 80 % ) are comparable to others for environments in southern Australia ( < 450mm average annual rainfall ). Such estimates of fixation are considered low ( < 65 % ) to adequate ( 65 - 80 % ). Nevertheless, the amount of plant available N present at sowing for subsequent wheat crops, and the occurrence of ' haying off ', suggests that WUE is not N - limited per se, as implied by some reports, but constrained by the capacity of a soil to balance the co - limiting factors of water and nitrogen. / Thesis (Ph.D.)--School of Earth and Environmental Sciences, 2005.

In the semi - arid Mediterranean - type environments of southern Australia, soil and water resources largely determine crop productivity and ultimately the sustainability of farming systems within the region. The development of sustainable farming systems is a constantly evolving process, of which cropping sequences ( rotations ) are an essential component. This thesis focused on two important soil resources, soil water and nitrogen, and studied the effects of different crop sequences on the dynamic of these resources within current farming systems practiced on the upper Eyre Peninsula of South Australia. The hypothesis tested was that : continuous cropping may alter N dynamics but will not necessarily alter water use efficiency in semi - arid Mediterranean - type environments. Continuous cropping altered N - dynamics ; increases in inorganic N were dependent on the inclusion of a legume in the cropping sequence. Associated with the increase in inorganic N supply was a decrease in WUE by the subsequent wheat crop. Overall, estimates of water use efficiency, a common index of the sustainability of farming systems, in this study concur with reported values for the semi - arid Murray - Mallee region of southern Australia and other semi - arid environments worldwide. Soil water balance and determination of WUE for a series of crop sequences in this thesis suggests that the adoption of continuous cropping may increase WUE and confer a yield benefit compared to crop sequences including a legume component in this environment. No differences in total water use ( ET ) at anthesis or maturity were measured for wheat regardless of the previous crop. Soil evaporation ( E [subscript s] ) was significantly affected by crop canopy development, measured as LAI from tillering until anthesis in 2002, however total seasonal E [subscript s] did not differ between crop sequences. Indeed in environments with infrequent rainfall, such as the upper Eyre Peninsula, soil evaporation may be water - limited rather than energy limited and the potential benefits from greater LAI and reduced E [subscript s] are less. Greater shoot dry matter production and LAI due to an enhanced inorganic N supply for wheat after legumes, and to a lesser degree wheat after canola, relative to continuous cereal crop sequences resulted in increases in WUE calculated at anthesis, as reported by others. Nonetheless the increase in WUE was not sustained due to limitations on available soil water capacity caused by soil physical and chemical constraints. Access to more soil water at depth ( > 0.8m ) through additional root growth was unavailable due to soil chemical limitations. More importantly, the amount of plant available water within the ' effective rooting depth ' ( 0 - 0.8m ) was significantly reduced when soil physical factors were accounted for using the integral water capacity ( IWC ) concept. The difference between the magnitude of the plant available water capacity and the integral water capacity was approximately 90mm within the ' effective rooting depth ' when measured at field capacity, suggesting that the ability of the soil to store water and buffer against periodic water deficit was severely limited. The IWC concept offers a method of evaluating the physical quality of soils and the limitations that these physical properties, viz. aeration, soil strength and hydraulic conductivity, impose on the water supply capacity of the soil. The inability of the soil to maintain a constant supply of water to satisfy maximal transpiration efficiency combined with large amounts of N resulted in ' haying off ', and reduced grain yields. A strong negative linear relationship was established between WUE of grain production by wheat and increasing soil NO [subscript 3] - N at sowing in 2000 and 2002, which conflicts with results from experiments in semi - arid Mediterranean climates in other regions of the world where applications of N increased water use efficiency of grain. Estimates of proportional dependence on N [subscript 2] fixation ( % N [subscript dfa] ) for annual medics and vetch from this study ( 43 - 80 % ) are comparable to others for environments in southern Australia ( < 450mm average annual rainfall ). Such estimates of fixation are considered low ( < 65 % ) to adequate ( 65 - 80 % ). Nevertheless, the amount of plant available N present at sowing for subsequent wheat crops, and the occurrence of ' haying off ', suggests that WUE is not N - limited per se, as implied by some reports, but constrained by the capacity of a soil to balance the co - limiting factors of water and nitrogen. / Thesis (Ph.D.)--School of Earth and Environmental Sciences, 2005.

Tyrimai atlikti 2008–2009 m. Lietuvos žemės ūkio universiteto Bandymų stotyje. Dirvožemis – karbonatingas sekliai glėjiškas išplautžemis (Calc(ar)i-Epihypogleyic Luvisol). Tyrimo A veiksnys – 4 septynių narių sėjomainų rotacijos su nevienoda azotą fiksuojančių augalų dalimi: I – 43 proc. (daugiametės žolės → daugiametės žolės → žieminiai kviečiai → vasariniai miežiai → žirniai → žieminiai kviečiai → miežiai), II – 43 proc. (daugiametės žolės → žieminiai kviečiai → žirniai → vasariniai miežiai su įsėliu → daugiametės žolės → žieminiai kviečiai → miežiai), III – 29 proc. (daugiametės žolės → bulvės → belukštės avižos → vasariniai miežiai → žirniai → žieminiai kviečiai → miežiai), IV – 14 proc. (daugiametės žolės → žieminiai kviečiai → bulvės → vasariniai miežiai → žieminiai rapsai → žieminiai kviečiai → miežiai). Veiksnys B – tarpinis pasėlis žaliajai trąšai: 1) be tarpinio pasėlio, 2) tarpinis pasėlis žaliajai trąšai. Nustatyta, kad sėjomainos piktžolių sėklų atsargoms dirvoje esminės įtakos neturėjo. Tarpinis pasėlis žaliajai trąšai, lyginant su jo nenaudojimu, turėjo tendenciją mažinti nuo 5,4 iki 44,2 proc. piktžolių sėklų atsargas dirvoje. Piktžolės pasiskirstė į 4 ekologines grupes pagal poreikį dirvožemio pH, azotui ir drėgnumui. Didžiausias sėklų kiekis dirvoje nustatytas indiferentiškų pagal poreikį dirvožemio pH ir drėgnumui, mažo rūgštumo ir silpnai šarminių dirvožemių piktžolių rūšių, azoto turtinguose dirvožemiuose augančių dažniau negu neturtinguose bei... [toliau žr. visą tekstą] / Field experiments were carried out in 2008 and 2009 at the Experimental Station of Lithuanian University of Agriculture. The objective of this investigation was to determine the influence of crop rotations and catch crops for green manure on weed seed-bank and soil enzymes urease and saccharase activity in the organic farming. Soil – Calc(ar)i-Epihypogleyic Luvisol. Factor A of the experiment – crop rotations with a different ratio of nitrogen fixing crops: I – 43% (grass-clover→grass-clover→winter wheat→spring barley→peas→winter wheat→spring barley), II – 43% (grass-clover→winter wheat→peas→spring barley→grass-clover→winter wheat→spring barley), III – 29% (grass-clover→potato→oat→spring barley→peas→winter wheat→spring barley), IV – 14% (grass-clover→winter wheat→potato→spring barley→winter rape→winter wheat→spring barley). Factor B – catch crop: 1) without catch crop, 2) with catch crop. Crop rotations had no significant effect on weed seed-bank. Catch crop for green manure, compared to without catch crop, decreased from 5.4 to 44.2% the amount of weed seeds. Weeds distributed into 4 ecological groups according to soil pH, nitrogen and soil moisture demand. The highest amount of weed seeds belonged to indifferent to soil pH and moisture, slightly acid and slightly alkaline soil, more frequent on nitrogen rich soil than on poor and moderately nitrogen rich soil and very nitrogen rich soil, dry and moderately moist soil weed species. Qualitative distribution of weeds into... [to full text]

A study was conducted to determine (1) the N contribution of lentil (<i>Lens culinaris</i> Medikus) and its effect on subsequent wheat (<i>Triticum aestivum</i> L.) crops in the Dark Brown and Brown soil zones of Saskatchewan, (2) if synchronization of available N contributes to the rotation benefit, and (3) N fertilizer replacement value of the N effect of lentil on the subsequent wheat crop. Two approaches were used: a landscape-scale study established at Dinsmore in 1994, and a repeated small-plot study established at several locations (Dinsmore, 1993 and 1994; Clavet, Conquest, Eston and Zealandia, 1995). In the landscape-scale study, N2 fixation by lentil ranged from 28 to 46 kg ha-1, with an average of 34 kg ha -1 N and an N balance of -36 kg ha-1. In the small-plot study, N2 fixation ranged from 10 to 112 kg ha -1 with an average of 59 kg ha-1 N and an N balance of -22 kg ha-1. In the landscape-scale study, preseeding available N on the rotation that incorporated lentil was 29 and 61% higher than in the monocropped wheat in the first and second subsequent crops, respectively. The corresponding values for the small-plot study were 59 and 14%, respectively. N availability was well synchronized with the period of maximum N demand by the wheat crop in both rotations. However, both lentil-residue N and wheat-residue N were poorly synchronized with the period of maximum N demand by the wheat. The rotation effect was exhibited in higher grain yield (23% higher in the landscape-scale study, and 21% higher in the small-plot study). Approximately 10 and 70% of the rotation benefit in the landscape-scale and small plot studies, respectively, were attributed to the N effect. Nitrogen fertilizer replacement value ranged from 47 to 89 kg ha-1 N. Therefore, lentil can fix enough N and indirectly contribute to greater available N in subsequent crops than in crops following non-legumes. However, the actual amount of N derived from lentil residue is small. The greater available N is attributed to spared N and enhanced soil N mineralization. Hence, under the conditions of this study, enhancement of available N contributed more to the rotation benefit than synchronization. The high NFRV show that inclusion of lentil in the rotation can enhance available N in the cropping system and potentially reduce fertilizer N application.

The thesis focuses on catch crops and crop rotation used in conventional agriculture and the possibility of their utilization in anti-erosion protection. The thesis includes a research which describes land consolidation and the main territorial systems which allow anti-erosion protection. Different kinds of erosion and the crop rotation are described in this thesis. The chapter about catch crops is focused on the inclusion of catch crops into the crop rotation. The goal of this study is to assess the real suggested actions used during the land consolidation and to compare their effectiveness with the effectiveness of crop rotation including catch crops.

This thesis analyses buckwheat as a cover crop in Florida. The study was designed to demonstrate: soil enrichment with nutrients, mycorrhizal arbuscular fungi interactions, growth in different soil types, temperature limitations in Florida, and economic benefits for farmers. Buckwheat was planted at the FIU organic garden (Miami, FL) in early November and harvested in middle December. After incorporation of buckwheat residues, soil analyses indicated the ability of buckwheat to enrich soil with major nutrients, in particular, phosphorus. Symbiosis with arbuscular mycorrhizal fungi increased inorganic phosphorus uptake and plant growth. Regression analysis on aboveground buckwheat biomass weight and soil characteristics showed that high soil pH was the major limiting factor that affected buckwheat growth. Spatial analysis illustrated that buckwheat could be planted in South Florida throughout the year but might not be planted in North and Central Florida in winter. An economic assessment proved buckwheat to be a profitable cover crop.

L’agriculture biologique (AB) est souvent présentée comme une alternative prometteuse à l’agriculture conventionnelle, permettant des systèmes alimentaires durables tout en minimisant les impacts environnementaux. La capacité de l’AB à satisfaire la demande alimentaire mondiale reste néanmoins fortement débattue. Plusieurs études ont conclu que l’AB pourrait satisfaire la demande alimentaire globale à condition de réduire simultanément la consommation de produits animaux et les gaspillages. Cependant, ces études n’ont pas pleinement pris en compte les changements d’assolement et de choix d’espèces lorsque les systèmes conventionnels sont convertis en AB. Surtout, ils ont ignoré le rôle clé de la disponibilité en azote (N) dans le maintien des rendements en AB. Dans cette étude, nous avons d’abord réalisé une méta-analyse comparant les rotations de cultures en agriculture biologique et conventionnelle à l’échelle mondiale. Sur la base de ces résultats, nous avons développé une cartographie des espèces cultivées à l’échelle globale sous un scénario de fort développement de l’AB. Nous avons ensuite estimé la production alimentaire grâce au développement de GOANIM (Global Organic Agriculture NItrogen Model), un modèle biophysique et spatialement explicite d’optimisation linéaire simulant le cycle de l’azote (N) et ses effets sur la production alimentaire globale. GOANIM est adapté au cas de l’AB et simule les flux d'azote entre les terres cultivées, les animaux d'élevage et les prairies permanentes, ainsi qu’entre les systèmes agricoles biologiques et conventionnels. Le modèle optimise les populations d’élevage à l’échelle locale afin de maximiser l’approvisionnement en N provenant du fumier, ce qui maximise la production issue des terres cultivées, tout en minimisant la concurrence exercée par les animaux pour les ressources alimentaires. GOANIM a été utilisé pour simuler l’offre alimentaire sous plusieurs scénarios de conversion à l’AB. Ces résultats ont été comparés à différentes estimations de la demande alimentaire mondiale. Nous montrons que la carence en N risque d’être un facteur limitant majeur de la production en AB, entraînant une réduction de -37% de la disponibilité alimentaire à l’échelle globale sous un scénario de conversion à l’AB de 100%. Nous montrons que des taux de conversions inférieurs (jusqu'à 60% des terres agricoles), en coexistence avec l'agriculture conventionnelle, permettent de satisfaire la demande alimentaire mondiale si cette conversion est associée à une évolution conjointe de la demande, telle que la réduction de l'apport énergétique par individu ou du gaspillage alimentaire. Ces travaux contribuent de manière substantielle à mieux comprendre le rôle que l’AB peut jouer dans la transition vers des systèmes alimentaires équitables et durables. Ils indiquent également des voies à suivre pour parvenir à la sécurité alimentaire mondiale. / Organic agriculture is often proposed as a promising approach to achieve sustainable food systems while minimizing environmental impacts. Its capacity to meet the global food demand remains, however, debatable. Some studies have investigated this question and have concluded that organic farming could satisfy the global food demand provided that animal product consumption and food waste are reduced. However, these studies have not fully considered the changes in the type of crops grown that occur when conventional farming systems are converted to organic farming. Most importantly, they also have missed a critical ecological phenomenon by not considering the key role that nitrogen (N) cycling plays in sustaining crop yields in organic farming. In this study, we first carried out a global meta-analysis comparing organic vs conventional crop rotations. Based on these results, we developed global spatial explicit maps of the type of crop grown if organic farming was to drastically expand. We then estimated organic global food production using GOANIM (Global Organic Agriculture NItrogen Model), a spatially explicit, biophysical and linear optimization model simulating N cycling in organically managed croplands and its feedback effects on food production. GOANIM explores N flows between croplands, livestock animals and permanent grasslands, and with conventional farming systems. The model optimizes livestock populations at the local scale in order to maximize N supply from livestock manure – hence maximizing cropland production –, while minimizing the animals’ competition for grain food resources. We used GOANIM to simulate several supply-side scenarios of global conversion to organic farming. We then compared the outcomes of these scenarios with different estimates of the global demand, thus leading to complete exploration of the global production-demand options space. We show N deficiency would be a major limiting factor to organic production in a full organic world, leading to an overall -37% reduction in global food availability. Nevertheless, we also show that lower conversion shares (up to 60%) would be feasible in coexistence with conventional farming when coupled with demand-side solutions, such as reduction of the per capita energy intake or food wastage. This work substantially contributes to advancing our understanding of the role that organic farming may play to reach fair and sustainable food systems, and it indicates future pathways for achieving global food security.

Les champignons de la rhizosphère ont une grande influence sur le développement et la croissance des plantes. Certains de ces micro-organismes protègent les plantes contre les pathogènes, atténuent l'impact des stress abiotiques ou facilitent la nutrition des plantes. Ces organismes s'influencent mutuellement et forment des réseaux complexes d'interactions. Déterminer le fonctionnement du microbiome fongique de la rhizosphère des plantes cultivées est une étape nécessaire pour optimiser l'efficacité de la production végétale. Nous avons testé les hypothèses suivantes : (1) la diversification des systèmes de culture influe sur le microbiome fongique de la rhizosphère du canola; (2) le canola a un core microbiome, soit un ensemble de champignons toujours associés au canola quelles que soit les conditions du milieu; et (3) que certains de ces taxons ont une influence déterminante sur la structure des communautés (taxons nodaux) dans le core microbiome. Pour ce faire, en 2013 et 2016, nous avons échantillonné à la floraison, la phase de canola (Brassica napus) du système de culture, qui est l'un des deux types de canola (Roundup Ready® et Liberty Link®), utilisés dans le cadre d'une expérience de terrain à long terme (6 ans). Lacombe (Alberta), Lethbridge (Alberta) et Scott (Saskatchewan). En utilisant le séquençage d’amplicon par illumina, nous avons obtenus des résultats qui montrent que la diversification des cultures a un impact significatif sur la structure des communautés fongiques de la rhizosphère. Nous avons également découvert et décrit un core microbiome constitué de 47 OTU (Unité Taxonomique Opérationnelle) en 2013 et identifié Preussia funiculata, Schizothecium sp., Mortierella sp., Nectria sp. ainsi que deux taxons inconnus (OTU12 et OTU298) comme taxons nodaux parmi ce core microbiome. Cependant ce core microbiome s’est montré variable, et nous n’avons pu identifier qu’un OTU y appartenant en 2016 : Olpidium Brassicae. Nos résultats permettent de confirmer l’impact de la diversité culturale sur le microbiome fongique du canola et sont présentés comme une base pour le développement de stratégies d'ingénierie écologique pour l'amélioration de la production de canola. / The fungi in the rhizosphere have a large influence on plant development and growth. Some of these micro-organisms protect plants against pathogens, mitigate the impact of abiotic stress, or facilitate plant nutrition. These organisms influence each other and form complex webs of interactions. Deciphering the structure and function of the fungal microbiome of crop plant rhizosphere is a necessary step toward optimizing the efficiency of plant production. We tested the hypotheses that (1) the diversification of cropping systems influences the fungal microbiome of canola rhizosphere, (2) canola has a fungal core microbiome, i.e. a set of fungi that are always associated with canola, and (3) that some taxa have a determining influence on the structure of the communities (hub-taxa) within the core microbiome. In 2013 and 2016 we used the canola (Brassica napus) phase of five cropping system at blooming stage, from the less to the most diversified, that included one of two types of canola (Roundup Ready® and Liberty Link®), in an existing long-term (6 years) field experiment. The experiment has a randomized complete block design with four blocks, and is replicated at three locations: Lacombe (Alberta), Lethbridge (Alberta) and Scott (Saskatchewan). Our results show that crop diversification has significant impact on the structure of rhizosphere fungal communities. We also discover and described a canola core microbiome made of 47 OTUs in 2013 and identified Preussia funiculata, Schizothecium sp., Mortierella sp., Nectria sp. and two other unidentified taxa (OTU12 and OTU298) as the hub-taxa among this core. However this core microbiome was variable and could identify only one member in 2016 : Olpidium brassicae. Our results confirmed the effect of crop diversification upon the fungal microbiome of canola and are presented as a basis for the development of ecological engineering strategies for the improvement of canola production.