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Thesis (MscAgric (Animal Sciences))--University of Stellenbosch, 2007. / The effect of a multiple-enzyme combination in mash and pelleted vegetarian maize-soya diets for broilers was evaluated in terms of apparent excreta- and ileal nitrogen- and amino acid digestibility and production performance. Two separate digestibility trials and one performance trial were conducted. For Trial 1, the apparent nitrogen (N) - and amino acid (AA) digestibility was determined by the collection of the excreta (total collection method) and in Trial 2 from digesta collected at the terminal ileum (ileal digestibility method). Production performance was also recorded in Trial 1. In Trial 3, the effect of the multipleenzyme combination in potentially improving performance of broilers in commercial conditions was evaluated. Broilers were fed a balanced- and low apparent energy (AME) vegetarian maize-soya diet with the addition of the multiple-enzyme combination. The addition of enzymes improved the apparent excreta- and ileal N digestibility of the mash diets during the period 14-21 d, and the ileal N-digestibility of the pelleted diets at 28 and 35 d of age. Conflicting results with regard to apparent excreta- and ileal AA digestibility were found. By both methods the digestibilities of threonine (Thr), methionine (Met) and phenylalanine (Phe) (14-21 d) and Cys (22-28 d and 29-35 d) were improved by the addition of the enzyme combination to the mash diets. Over the entire experimental period (14-35 d) the ileal digestibilities of histidine (His), Cys and leucine (Leu)of the mash diets were improved by 0.2 %, 0.2 % and 1.9 % respectively, following enzyme addition. By both methods the digestibilities of Thr, arginine (Arg), Met, Cys, Phe and Leu (14-21 d), serine (Ser), Arg, glutamic acid (Glu), Val, His, aspartic acid (Asp), lysine (Lys), proline (Pro), Met, tyrosine (Tyr), Phe and Leu (22-28 d), and Pro (29-35 d) were improved by the combination of enzymes and pelleting. For the entire experimental period (21-35 d), the ileal digestibilities of Ser, His, Lys, Met, Tyr, Cys, Phe and Leu was improved by the combination of enzymes and pelleting, indicating enzymatic activity was not destroyed by cold pelleting at 60 - 80º. The improvements in apparent nitrogen- and AA digestibilities were, in most cases, not reflected in production performance, although the combination of enzymes and pelleting resulted in improved body weight gain (BWG) for the first two weeks of chicks life and significantly improved the feed conversion ratio (FCR) during the second week of the chicks’ life. The effect of the multiple-enzyme combination on the production performance of broilers on a low AME- and commercial diet was mostly non-significant except for a significantly lower feed iii intake of the balanced diet for the fourth and fifth week of chick’s life following enzyme addition. A financial calculation showed, however, that the enzyme combination might increase profitability of a nutritionally balanced vegetarian maize-soya diet for broilers.

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Thesis (M.S.)--University of Delaware, 2005. / Principal faculty advisors: John C. Bernard and John D. Pesek, Dept. of Food and Resource Economics. Includes bibliographical references.

Orientador: Ciniro Costa / Coorientador: Luiz Gustavo Nussio / Coorientador: Paulo Roberto de Lima Meirelles / Banca: Cyntia Ludovico Martins / Banca: Thiago Fernandes Bernardes / Banca: Maity Zapollato / Banca: Danilo Domingues Millen / Resumo: O objetivo deste estudo foi avaliar o efeito do processamento das plantas de milho na ensilagem sobre o desempenho de bovinos confinados. Foram utilizados 72 animais da raça Nelore com idade aproximada de dezoito meses e peso vivo inicial de 392,80 ± 24,42kg. O delineamento experimental foi inteiramente casualizado em arranjo fatorial 2 x 2 (processamentos e relação concentrado:volumoso). Não houve interação para as variáveis consumo de matéria seca e conversão alimentar. Houve efeito significativo para silagem e relação concentrado:volumoso no consumo de matéria seca em função do peso metabólico. O maior consumo foi observado com a silagem processada e para a relação concentrado volumoso de 60:40. Para o consumo de matéria seca/dia houve efeito somente na relação concentrado:volumoso, sendo o maior consumo para a relação 60:40. A conversão alimentar apresentou diferença somente para o período, sendo a melhor conversão para o 1º período. Para ganho de peso houve interação para silagem e relação concentrado:volumoso. Verificou-se menor consumo para a silagem processada na relação 80:20. Porém, para a silagem não processada não foi observada diferença entre as relações concentrado:volumoso. A colheita do milho para silagem, no estádio de maturidade fisiológica dos grãos, associada ao processamento da massa durante a ensilagem, permite balancear dietas com 60% de concentrado para tourinhos não castrados confinados / Abstract: A study involving a 2 x 2 factorial arrangement of treatments was conducted to evaluate effects of corn silage processing and concentrate-to-forage ratio on feedlot cattle performance. 72 Nelore breed aged approximately eighteen months (392.80 ± 24.42 kg BW) were used. No significant interaction was observed between dry matter intake and feed conversion ratio. There was observed a significant effect of silage and concentrate-to-forage ratio on dry matter intake due to metabolic weight. The highest consumption was observed for the processed corn silage at concentrate-toforage ratio 60:40. Related to dry matter intake/day there was a significant effect only for concentrate-to-forage ratio, being the highest intake on 60% forage and 40% concentrate. There was a significant effect for feed conversion ratio only for the period, being the best one observed for the 1st period. Related to weight gain there was an interaction for silage and concentrate-to-forage ratio. It was determined less consumption for processed corn silage on concentrate-to-forage ratio 80:20. However was not observed effect on unprocessed corn silage between concentrate-to-forage ratio. The harvest of corn for silage, at physiological maturity of the grains associated with the processing of silage mass during ensilage, allows diets with 60% of concentrate for Nelore breed feedlot

Changes in cell wall composition and in vitro degradation of corn stover fractions (leaf, upper stem and lower stem) with advancing maturity and in response to NH; treatment were determined, and possible inhibitory mechanisms of lignin were evaluated. With advancing maturity, IVDMD decreased (P<.001), associated with decreases (P<.001) in CP and water soluble carbohydrates (WSC), and increases (P<.001) in NDF and ADF. The IVDMD of leaf was higher (P<.001) than of stems, associated with higher CP, hemicellulose:cellulose, and arabinan:xylan, and lower lignin methoxyl content. A hypothesis of formation of reactive quinone methide intermediates from lignin during rumen fermentation was tested in vitro by incubating corn stover fractions with S-containing reducing agents. Sulphur incorporation into residual fiber occurred (P<.05), indicative of nucleophilic addition to quinone methide intermediates. Degradation of NDF was highly correlated with lignin methoxyl content. The impact of lignin on cellulose degradation was studied using lignocellulosic hydrogels, in which hydroxypropylated or unmodified hardwood lignin was blended with cellulose. In vitro cellulose degradation of lignocellulose blends was higher (P<.01) than of control. Addition of lignin at incubation depressed (P<.01) cellulose degradation. Hydroxypropylation enhanced (P<.001) the increase in cellulose degradation with lignin blending, and reduced (P<.001) the inhibitory effect of lignin addition at incubation. Treatment of drought-stressed corn stover with 3% aqueous NH₃ decreased (P<.05) NDF, compared to isonitrogenous NH₃ addition and control, associated with solubilization of hemicellulose. Esterified phenolic acids were released (P<.05) by NH₃ treatment in upper stem. The IVDMD and NDF degradation increased (P <.001) after ammoniation, with higher (P<.05) values for NH₃ treatment than NH₃ added in leaf. The in vitro response to ammoniation of fractions of drought-stressed and non-drought stressed corn stover harvested in subsequent years was compared, using N-sufficient and N-limiting buffers. Response was highest (P<.001) for non-drought stressed stover fractions, and in N-limiting medium. Response appeared to be affected by high concentration of WSC in lower stalks of drought-stressed stover. / Ph. D.

Thesis (MScAgric (Animal Sciences))--University of Stellenbosch, 2011. / Includes bibliography. / ENGLISH ABSTRACT: A growth and digestibility trial was conducted comparing the effect of an experimental enzyme at three different inclusions. A negative control containing no enzyme additions and a positive control containing a proven commercial enzyme were compared in a maize-soybean diet noting the performance of broilers and the digestibility of the grower feed. The commercial enzyme was a granular product with a xylanase activity of 38114.29 nkat/g and the second enzyme (ABO374) was a liquid experimental product with a xylanase activity of 1426.86 nkat/ml. Five diets were used i.e. control basal diet without enzyme supplementation (negative control), basal diet supplemented with the commercial enzyme (positive control) and three basal diets supplemented with the test enzyme at various inclusion levels (ABO 50, ABO 100 and ABO 200). The positive control was supplemented with 200 g/ton of the commercial enzyme; ABO 50 was supplemented with ABO374 at an inclusion level of 2671 ml/ton, ABO 100 with 5342 ml/ton and ABO 200 with 10684 ml/ton. Supplementation with the test enzyme (ABO 50) significantly improved BW at 23 days of age by 4.6 % (1107.4 g vs 960.96 g) and at 37 days of age by 3.2 % (2311.75 g vs 2237.81 g) over the negative control. Body weight gain for the total period of the trial was significantly improved by 3.24 % (64.32 g/bird/day vs 62.24 g/bird/day) the test enzyme supplementation (ABO 50) when compared to the negative control. During the starter phase, test enzyme supplementation (ABO 50) led to an improvement of 4.58 % (1.25 vs 1.31) in FCR in comparison with the negative control. The FCR for the total trial obtained by the test enzyme supplementation was significantly lower than the FCR obtained by the positive control. The highest EPER obtained for this trail was by the test enzyme supplemented diets and this was significantly higher than the EPER obtained by the positive control. It is clear from this growth trial that the test enzyme (ABO374) at an inclusion level of 2671 ml/ton outperformed the commercial enzyme and that it has the potential to improve the production performance of broilers on a maizeSBM based diet. The total tract digestibility method and total collection method was used to conduct the digestibility trial. The total tract digestibility method measures the difference between the amounts of each nutrient consumed from the amounts of each nutrient excreted in faeces. Only apparent digestibilities are reported for the digestibility trial. Apparent digestibility does not take the endogenous protein fraction in the faeces into account. The endogenous protein fraction is derived from digestive enzymes and proteins from the intestinal walls that are secreted into the digestive tract. The grower negative control, positive control, ABO 50, ABO 100 and ABO 200 diets used in the production trial were also used in the digestibility trial. Supplementation with the test enzyme showed no significant improvements on the apparent digestibility of dry matter, organic material, ash, crude protein, metabolisable energy or crude fibre. No significant improvements in the apparent digestibility of the amino acids (threonine, arginine, valine, lysine, methionine, cysteine and isoleucine) were noticed either and thus the digestibility of the grower feed were not influenced by the addition of enzymes due to the supplementation of the test enzyme ABO374. Pelletisation of the grower diets could have lead to the inactivation of the enzyme due to the high temperature at which pelletisation takes place. Another possible reason why enzyme supplementation did not increase nutrient digestibility, may be that the breakdown of non-starch polysaccharides by the enzymes led to an increase in the concentration of oligosaccharides in the small intestine of the birds, thus leading to the decrease in nutrient absorption Key words: body weight, body weight gain, feed conversion ratio, European production efficiency ratio, maize, soybean meal, apparent digestibility, dry matter, organic material, ash, crude protein, metabolisable energy, crude fibre, xylanase, pellitisation. / AFRIKAANSE OPSOMMING: ‘n Groei en vertering studie was uitgevoer om die effek van ‘n eksperimentele ensiem wat teen drie verskillende insluitingsvlakke by ‘n basale dieët bygevoeg is te vergelyk met ‘n negatiewe kontrole wat geen ensiem bevat het nie en met ‘n positiewe kontrole wat ‘n kommersiële ensiem bevat in ‘n mielesojaboon oliekoek dieët op die produksie vermoë van braaikuikens en die verteerbaarheid van die groei voer. Die kommersiële ensiem was ‘n granulêre produk met ‘n xylanase aktiwiteit van 38114.29 nkat/g en die eksperimentele ensiem (ABO374) was ‘n vloeistof produk met ‘n xylanase aktiwiteit van 1426.86 nkat/ml. Vyf diëte was gebruik nl. ‘n basale dieët met geen ensiem byvoeging (negatiewe kontrole), basale dieët met die byvoeging van die kommersiële ensiem (positiewe kontrole) en drie basale diëte wat met die byvoeging van die eksperimentele ensiem teen drie verskillende insluitings vlakke (ABO 50, ABO 100 and ABO 200). Die kommersiële ensiem was by die positiewe kontrole bygevoeg met ‘n insluitings vlak van 200 g/ton, ABO374 was bygevoeg by ABO 50 met ‘n insluitings vlak van 2671 ml/ton, ABO 100 met 5342 ml/ton en ABO 200 met 10684 ml/ton. Die byvoeging van die eksperimentele ensiem (ABO 50) het gelei tot die betekenisvolle verbetering van die liggaamsmassa van die voëls by die ouderdom van 23 dae met 4.6 % (1107.4 g teenoor 960.96 g) en by die ouderdom van 37 dae met 3.2 % (2311.75 g teenoor 2237.81 g) teenoor die negatiewe kontrole. Liggaams massa toename vir die hele periode van die studie was betekenisvol verhoog met 3.24 % (64.32 g/kuiken/dag teenoor 62.24 g/kuilen/dag) met die byvoeging van die eksperimentele ensiem (ABO374) teenoor die negatiewe kontrole. Voeromset verhouding was betekenisvol verbeter met 4.58 % (1.25 teenoor 1.31) toe die kommersiële ensiem bygevoeg was teenoor die negatiewe kontrole. Die hoogste europese produksie effektiwiteits verhouding wat verkry is vir die hele studie periode is deur die byvoeging van die eksperimentele ensiem (ABO374). Hierdie groei studie dui dus duidelik aan dat die gebruik van die eksperimentele ensiem (ABO374) baie beter resultate as die kommersiële ensiem opgelewer het teen ‘n insluitings vlak van 2671 ml/ton, dus het ABO374 die potensiaal om die produksie potensiaal van braaikuikens op ‘n mielie-sojaboonoliekoek dieët te verbeter. Die totale spysverteringskanaal verteerbaarheid metode was gebruik om die verteerbaarheid studie uit te voer. Die totale spysverteringskanaal verteerbaarheid metode meet die verskil tussen die nutriënt inhoud van die voer en die nutriënt inhoud van die mis. Slegs die skynbare verteerbaarheid van nutriënte word vir hierdie verteerbaarheidstudie gerapporteer. Skynbare verteerbaarheid sluit nie die endogene proteïenfraksie wat afkomstig is van verteringsensieme of die proteïene afkomstig vanaf die spysverteringskanaal se intestinale wande af in nie. Die negatiewe kontrole, positiewe kontrole, ABO 50, ABO 100 en ABO 200 groei diëte gebruik in die produksie studie is gebruik vir die verteringsstudie. Die byvoeging van die eksperimentele ensiem het geen betekenisvolle resultate opgelewer ten opsigte van droë materiaal, organiese material, as, ru-proteïen, ru-vesel of metaboliseerbare energie nie. Daar was ook geen betekenisvolle resultate opgelewer wanneer die eksperimentele ensiem bygevoeg was nie ten opsigte van die verteerbaarheid vir aminosure (treonien, arginien, valien, metionien, sisteïen en isoleosien) nie en dus is die verteerbaarheid van die groeivoer glad nie beïnvloed deur die byvoeging van die eksperimentele ensiem nie. Die verpilling van die groei voer mag dalk gelei het tot die inaktivering van die eksperimentele ensiem deur dat dit blootgestel was aan hoë temperature. ‘n Ander moontlike rede vir die mislukking van die ensiem kon gewees het dat die afbreking van die nie-stysel polisakkariedes deur die ensiem kon gelei het tot die verhoging van die oligosakkariede konsentrasie in die laer spysverterings kanaal en dus kon dit lei tot ‘n verhoogde deurvloeitempo, gevolg deur ‘n afname in die absorpsie van nutriënte. Sleutel woorde: Liggaamsmassa, liggaamsmassa toename, voeromsetverhouding Europese produksie effektiwiteits verhouding, mielie, sojaboonoliekoek, skynbare verteerbaarheid, droëmaterial, organiesematerial, as, ru-proteïen, ru-vesel, metaboliseerbare energie, verpilling.

Thesis (MScAgric (Animal Sciences))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Kikuyu over-sown with ryegrass forms the basis of pasture based systems in the Southern Cape. During early spring, energy is the first limiting nutrient in kikuyu/ryegrass pasture, supplementation is thus essential. Supplementation consists mainly of high starch concentrates (high maize inclusion), which is expensive and could negatively affect rumen parameters. The objective of this study was to determine if milk production could be improved or maintained, and if the rumen environment would be improved, by replacing high starch concentrates with low starch (high by-product) concentrates for dairy cows on kikuyu/ryegrass pasture. Forty-five multiparous, high producing, lactating Jersey cows [body weight, 340 ± 34.7 kg; milk yield (MY), 19.6 ± 2.23kg/d; days in milk (DIM), 153 ± 33.5; lactation number, 3.6 ± 1.85; (mean ± SD)] were used in the production study. A randomised block design was used. The forty-five cows were allocated to fifteen groups of three each (blocking) on the basis of MY, DIM, and lactation number. Cows from each group were randomly allocated to one of three treatment groups (high starch, medium starch and low starch concentrate supplementation). Cows were fed 6kg (3kg during each milking) concentrate per day and were allocated fresh pasture ad lib after each milking. There were no significant differences (P > 0.05) found in milk yield and fat corrected milk yield between treatment groups. Milk fat percentage was significantly higher (P < 0.05) in the low starch treatment than in the high starch treatment. Milk fat yield was significantly higher (P < 0.05) in both the low starch and the medium starch treatment when compared to the high starch treatment. Milk protein and lactose percentages, as well as milk urea nitrogen and somatic cell count, did not differ significantly (P > 0.05) between treatments. Live weight change, as well as body condition score change, was unaffected (P > 0.05) by treatments indicating body reserves were not used to maintain milk production in the low starch treatment. A rumen metabolism study was also done with ten lactating, cannulated Jersey cows [body weight, 332 ± 56.3 kg; MY, 17.3 ± 1.73kg/d (mean ± SD)] were used. The cows were divided into two groups of five each, on the basis of lactation number, DIM, and MY. The five cows from each group were randomly allocated to one of two treatment groups (high starch and low starch concentrate supplementation) and used in a cross-over design. Cows were fed 6kg concentrate per day and were allocated fresh pasture ad lib after each milking. The volatile fatty acid (VFA) concentration was significantly higher (P < 0.05) in the high starch treatment when compared to the low starch treatment. The individual VFA’s, acetic-, propionic- and butyric acid concentrations were also significantly higher (P < 0.05) in the high starch treatments when compared to the low starch treatment. The acetic to propionic acid ratio was unaffected (P > 0.05) by treatment. Rumen ammonia-nitrogen concentration was significantly higher (P < 0.05) in the high starch treatment. Rumen pH was unaffected (P > 0.05) by supplementation type. The in sacco dry matter and neutral detergent fibre digestibilities of the kikuyu/ryegrass pasture were unaffected (P > 0.05) by treatment type. Results indicated that milk production could be maintained with low starch concentrates which also improved milk composition. Results further suggested that the rumen environment was relatively unaffected by low starch concentrate supplementation. / AFRIKAANSE OPSOMMING: Kikoejoe, oorgesaai met raaigras, vorm die basis van weidingstelsels in the Suid-Kaap. Tydens die lentemaande is energie die eerste beperkende voedingstof op kikoejoe/raaigras weidings, wat kragvoeraanvulling noodsaaklik maak. Aanvulling bestaan grootliks uit hoëstysel-kragvoer (hoë mielieinhoud) wat nie net duur is nie, maar dit kan ook die rumenomgewing benadeel. Die doel van die studie was om vas te stel of melkproduksievlakke onderhou kan word en of rumenomgewing verbeter kan word deur die vervanging van hoëstysel-kragvoer met laestysel-kragvoer (hoë neweprodukinhoud) vir melkkoeie op kikoejoe/raaigras weidingstelsels. Vyf-en-veertig meervoudige pariteit-, hoë produserende, lakterende Jerseykoeie [liggaamsmassa, 340 ± 34.7 kg; melkproduksie, 19.6 ± 2.23kg/d; dae in melk, 153 ± 33.5; laktasienommer, 3.6 ± 1.85; (gem ± standaardafwyking)] is gebruik vir die produksiestudie van die proef. Daar is gebruik gemaak van ‘n ewekansige blokontwerp. Die vyf-en-veertig koeie is opgedeel in vyftien groepe van drie elk, gebaseer op melkproduksie, dae in melk en laktasienommer. Koeie in elke groep is ewekansig aan een van drie behandelings (hoëstysel-, mediumstysel- of laestysel-kragvoeraanvulling) geallokeer. Koeie is daagliks 6kg (3kg tydens twee milkings) kragvoer gevoer en vars weiding was ad lib beskikbaar na elke melking. Daar was geen beduidende verskil (P > 0.05) in melkopbrengs of vet-gekorrigeerde melkopbrengs tussen die drie behandelings nie. Bottervetpersentasie was beduidend hoër (P < 0.05) in die laestyselbehandeling in vergelyking met die hoëstyselbehandeling. Bottervetopbrengs was beduidend hoër (P < 0.05) in beide die laestysel- en mediumstyselbehandelings in vergelyking met die hoëstyselbehandeling. Melkproteïen- en melklaktosepersentasies, asook melkureumstikstof en somatise seltelling, was onveranderd (P > 0.05) tussen behandelinge. Liggaamsmassa en liggaamskondisietelling het geen verskille (P > 0.05) getoon tussen behandelings nie, wat daarop dui dat liggaamsreserwes nie gebruik is om melkproduksie in die laestyselbehandeling te onderhou nie. ‘n Rumenmetabolismestudie is ook uitgevoer met tien lakterende, gekannuleerde Jerseykoeie [liggaamsmassa, 332 ± 56.3 kg; melkproduksie, 17.3 ± 1.73kg/d (gem ± standard afwyking)]. Die koeie is in twee groepe van vyf elk verdeel, gebasseer op laktasienommer, dae in melk en melkproduksie. Die vyf koeie van elke groep is in ‘n omslagontwerp gebruik en is ewekansig aan een van twee behandelings (hoëstysel- of laestysel-kragvoeraanvulling) geallokeer. Koeie het daagliks 6kg kragvoer ontvang en vars weiding was ad lib beskikbaar na elke melking. Die vlugtige vetsuurkonsentrasie was beduidend hoër (P < 0.05) in die hoëstyselbehandeling as in die laestyselbehandeling. Die individuele vlugtige vetsure naamlik asynsuur, propionsuur en bottersuur, was ook beduidend hoër (P < 0.05) in die hoëstyselbehandeling as in die laestyselbehandeling. Die asynsuur- tot propionsuurverhoudings het geen verskille (P > 0.05) tussen behandelings getoon nie. Rumen-ammoniakstikstof was beduidend hoër (P < 0.05) in die hoëstyselbehandeling as in die laestyselbehandeling. Rumen-pH het geen verskille (P > 0.05) getoon tussen behandelings nie. Die in sacco droëmateriaal- en neutraalbestande veselverteerbaarhede van kikoejoe/raaigras weiding het geen verskille (P > 0.05) tussen behandelings getoon nie. Die resultate het aangedui dat melkproduksie onderhou kan word en dat melksamestelling verbeter kan word met laestysel-kragvoeraanvulling. Resultate het ook daarop gedui dat die rumenomgewing nie noodwendig verbeter word deur die aanvulling van laestysel-kragvoer vir koeie op kikoejoe/raaigras weidings nie.

Master of Science

L’objectif de ce travail est d’améliorer la productivité du maïs fourrager (Zea mays L.) dans les sols calcaires tunisiens. En effet dans ces conditions édaphiques la plante se heurte à des problèmes d’ordre nutritionnel limitant l’absorption des 3 éléments essentiels.<p>C’est pourquoi nous voulons mettre au point une nouvelle technologie capable de contourner ces contraintes. En effet la fertilisation par voie foliaire associé à un désherbage de pré émergence serait l’approche la plus logique, capable d’apporter les éléments en fonction des besoins de la plante et de constituer par conséquent une alternative à des apports traditionnels au sol qui présentent un faible coefficient d’efficacité.<p>Pour cela nous voulons :<p>- étudier l’effet de la dose, de la dilution de l’engrais et de son association à un herbicide de post émergence sur la biomasse et l’absorption des éléments nutritifs de la plante et comparer ces effets à ceux d’une application traditionnelle au sol.<p>- Déterminer l’équilibre NPK permettant d’obtenir une croissance optimale de la plante et ceci par le biais d’une expérimentation de type factoriel. <p>- Enfin transposer ce mode de fertilisation en conditions réelles au champ, en intégrant également un désherbage de post émergence. <p>Enfin rechercher et doser, les deux molécules présentes dans l’herbicide, dans deux substrats (le sol et la plante) et étudier leur rétention à court terme :caractérisation des mécanismes d’adsorption et de désorption des deux molécules dans les deux types de sol utilisés. <p>Les résultats obtenus en conditions contrôlées ont mis en évidence le fait que la biomasse de la plante ainsi que la quantité d’éléments exportés par celle-ci sont gouvernées par un effet variétal et un effet dose. De plus certaines associations herbicide-engrais favorisent mieux que d’autres la croissance de la plante ainsi que l’absorption des éléments appliqués. <p>Les résultats de l’expérience de type factoriel ont montré qu’à doses égales, l’effet positif d’un apport foliaire est supérieur à celui de l’engrais apporté au sol. Ces effets positifs sont observés sur les différents paramètres étudiés (biomasse, absorption d’éléments, nutritifs, quantités exportés et coefficients apparents d’utilisation des 3 éléments appliqués).<p>L’utilisation du logiciel SPSS montre que la relation de la biomasse (poids sec) et la quantité d’éléments apportée est de type polynomial. L’équation ainsi obtenue nous a permis de calculer la production de matière sèche et de représenter les différentes surfaces de réponse.<p><p>Les résultats obtenus en conditions réelles, au champ ont montré également que l’engrais apporté sur le feuillage est le mode de fertilisation le plus efficient. Ces résultats ont montré également que pour tous les traitements, la quantité d’azote exporté par la plante, suit une courbe unimodale avec un maximum situé au prélèvement III, effectué 34 jours après le semis. Par contre les quantités de P et les quantités de K exportés augmentent de façon continue, depuis le prélèvement I (26 jours après le semis) jusqu’à la récolte finale (97 jours après le semis). C’est (l’épi +tige) qui exporte la plus grande quantité (pratiquement le double). Un effet pompe dû au traitement foliaire a été également observé. Cet effet stimule l’absorption des éléments nutritifs par les racines et permet une meilleure valorisation des réserves du sol. <p>En plus le désherbage de post émergence associé à l’engrais a montré une plus grande efficacité à l’égard de la flore adventice présente, en comparaison à l’application de l’herbicide seul ou associé à l’engrais appliqué au sol. <p>Le dosage des deux molécules herbicides en HPLC a montré que les teneurs des 2 molécules dans la plante et dans le sol sont inférieures à la limite de détermination.<p>(les limites de détection et de détermination ont été estimées respectivement à de valeurs de 0,02 et de 0,05 mg/kg de sol). Les coefficients de corrélation des droites d’étalonnage obtenues, sont supérieurs à 0,99 et le pourcentage de recouvrement se situe entre 84 et 104% (intervalle de confiance est de plus ou moins 18%). <p>Les isothermes d’adsorption obtenues dans le cas du 2,4-D sont respectivement de type L avec Kf = 0,9 et n inférieur (sol A) et de type C, avec Kf = 0,8 et n voisin de 1 (sol B). Ces résultas montrent qu’en présence d’un pH (alcalin), la molécule entant qu’acide faible est dissociée. Cette forme est peu retenue par les colloïdes du sol ce qui favorise son transfert ainsi que sa dégradation. <p>La normalisation, du coefficient de distribution Kd, à la teneur en matière organique et à la teneur en carbone organique montre que pour des horizons de 0-30, 30 – 60 et 60 -120 cm, les valeurs de KOM et KOC dans le sol A, restent pratiquement identiques dans les 3 horizons. Par contre dans le sol B ces coefficients sont plus faibles dans l’horizon supérieur (0-30 cm).<p>Par contre les isothermes d’adsorption de la carfentrazone ont mis en évidence l’absence de celle-ci et par conséquent la conversion de molécule en ses métabolites. / Doctorat en Sciences agronomiques et ingénierie biologique / info:eu-repo/semantics/nonPublished