Analysis of the effects of water and nitrogen supply on the yield and growth of durum wheat under semi-arid conditions in Tunisia

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Diagnostic des facteurs limitants du rendement du ble dur en parcelles d'agriculteurs dans une petite region semi-aride en Tunisie

National audienceIn order to determine the main limiting factors of wheat production in a semi-arid area of Tunisia, growth, yield, and yield components of durum wheat were measured in agricultural fields over 2 years with contrasting rainfall. They were compared with controls established under experimental conditions and published in a previous paper. Dry matter production, yield, and yield component were highly variable among and within a climatic year. Yield was mainly related to grain number for both years; grain and ear number variability depend on growth before anthesis. Comparison with the controls allowed us to determine the main periods when limiting factors applied. Poor seedbed control, weed infestation, nitrogen supply, and water availability during the growing season, were all identified as main limiting factors. Some of these are related to constraints from the cropping systems.Dans un article précédent (Latiri-Souki et al, 1992), on a paramétré des relations entre composantes du rendement du blé dur en climat semi-aride, en l’absence de facteurs limitants. Ces relations ont servi à établir un diagnostic des facteurs et conditions limitants rencontrés dans un réseau de parcelles d’agriculteurs lors de 2 années climatiquement contrastées. Pour chaque scénario climatique, on obtient une forte variabilité des rendements entre parcelles, fonction du nombre de grains par unité de surface et essentiellement déterminée avant la floraison. La maîtrise de la levée, la nutrition azotée et l’infestation en adventices se sont avérées chaque année des facteurs majeurs de variation des rendements

Elaboration du rendement du ble dur en conditions semi-arides en Tunisie : relations entre composantes du rendement sous differents regimes de nutrition azotee et hydrique

National audienceWe studied the yield components of durum wheat (Triticum durum Desf) under semi-arid conditions in Tunisia (fig 1). The relationships between several yield components were established in conditions where nitrogen and water were unlikely to be limiting. The level of each component was fitted to that of components determined during previous periods of the crop cycle. Resulting relationships were considered as describing the maximum values of each component. They were plotted together with coupled values of components observed in conditions where water or nitrogen could be limiting. This allowed diagnosis of the effects of varying levels of nitrogen and water supplies on each yield component. The experiments were carried out in two soils ("Tell" and "Hamri", see table II) and several levels of nitrogen fertilization (fig 2), for two years with contrasting rainfall. The relationships between yield components, observed in the wet year and for high levels of nitrogen supply had similar patterns compared with those established for wheat grown in temperate regions (table I). However, the values of fitted parameters (table III) were appreciably different. In "Tell" soil, the maximum levels of all yield components were reached during the wet year for nitrogen fertilization as low as 60 kg ha-1 applied at tillering and beginning of the stem elongation; in "Hamri" soil, the maximum levels could not be reached, even for a total nitrogen amount of 100 kg ha-1 yield components had very low levels during the dry year in the two soils, with no appreciable effect of fertilization (table IV). In both dry and wet years, yields correlated better with the number of kernels per m2 (fig 3) than with the kernel weight. This suggests that pre-anthesis environmental conditions had a overriding effect on yields (figs 4 and 5). The observed range of kernel weight was not large enough to induce high variations in yield, in spite of the wide range of water and nitrogen supply. We used these results to propose a way of deciding nitrogen fertilization in relationship with yield objective in wet conditions (table V).L’élaboration du rendement du blé dur en climat semi-aride tunisien est étudiée afin de disposer de références permettant le diagnostic de facteurs limitants au champ. On teste sur blé dur les relations entre composantes du rendement établies sur blé tendre en climat tempéré. En conditions où seuls la température et le rayonnement intercepté sont limitants, on obtient, sur blé dur, des relations analogues à celles établies sur blé tendre. Le paramétrage de ces relations est ici proposé. Le comportement du blé dur en conditions variables de nutrition azotée et hydrique au cours de 2 années de climat contrasté est étudié en utilisant les modèles préalables comme outils de diagnostic. Dans tous les cas, la principale composante liée au rendement est le nombre de grains par m2, qui dépend des conditions de croissance et de développement pendant la phase semis-floraison. La composante «poids d’un grain» est cependant affectée par les conditions d’alimentation hydrique, à travers la durée de la phase de remplissage du grain. On met en évidence en année humide l’influence du fractionnement de l’azote apporté sur plusieurs composantes du rendement. Une première formulation de références techniques sur la fertilisation azotée en conditions hydriques favorables est proposée et discutée

Diagnostic des facteurs limitants du rendement du ble dur en parcelles d'agriculteurs dans une petite region semi-aride en Tunisie

Dans un article précédent (Latiri-Souki et al, 1992), on a paramétré des relations entre composantes du rendement du blé dur en climat semi-aride, en l’absence de facteurs limitants. Ces relations ont servi à établir un diagnostic des facteurs et conditions limitants rencontrés dans un réseau de parcelles d’agriculteurs lors de 2 années climatiquement contrastées. Pour chaque scénario climatique, on obtient une forte variabilité des rendements entre parcelles, fonction du nombre de grains par unité de surface et essentiellement déterminée avant la floraison. La maîtrise de la levée, la nutrition azotée et l’infestation en adventices se sont avérées chaque année des facteurs majeurs de variation des rendements.In order to determine the main limiting factors of wheat production in a semi-arid area of Tunisia, growth, yield, and yield components of durum wheat were measured in agricultural fields over 2 years with contrasting rainfall. They were compared with controls established under experimental conditions and published in a previous paper. Dry matter production, yield, and yield component were highly variable among and within a climatic year. Yield was mainly related to grain number for both years; grain and ear number variability depend on growth before anthesis. Comparison with the controls allowed us to determine the main periods when limiting factors applied. Poor seedbed control, weed infestation, nitrogen supply, and water availability during the growing season, were all identified as main limiting factors. Some of these are related to constraints from the cropping systems

Diagnostic des facteurs limitants du rendement du blé dur en parcelles d'agriculteurs dans une petite région semi-aride en Tunisie

Dans un article précédent (Latiri-Souki et al, 1992), on a paramétré des relations entre composantes du rendement du blé dur en climat semi-aride, en l'absence de facteurs limitants. Ces relations ont servi à établir un diagnostic des facteurs et conditions limitants rencontrés dans un réseau de parcelles d'agriculteurs lors de 2 années climatiquement contrastées. Pour chaque scénario climatique, on obtient une forte variabilité des rendements entre parcelles, fonction du nombre de grains par unité de surface et essentiellement déterminée avant la floraison. La maîtrise de la levée, la nutrition azotée et l'infestation en adventices se sont avérées chaque année des facteurs majeurs de variation des rendements.Diagnosis of durum wheat yield in agricultural fields under semi-arid conditions in Tunisia. In order to determine the main limiting factors of wheat production in a semi-arid area of Tunisia, growth, yield, and yield components of durum wheat were measured in agricultural fields over 2 years with contrasting rainfall. They were compared with controls established under experimental conditions and published in a previous paper. Dry matter production, yield, and yield component were highly variable among and within a climatic year. Yield was mainly related to grain number for both years; grain and ear number variability depend on growth before anthesis. Comparison with the controls allowed us to determine the main periods when limiting factors applied. Poor seedbed control, weed infestation, nitrogen supply, and water availability during the growing season, were all identified as main limiting factors. Some of these are related to constraints from the cropping systems

Élaboration du rendement du blé dur en conditions semi-arides en Tunisie : relations entre composantes du rendement sous différents régimes de nutrition azotée et hydrique

L'élaboration du rendement du blé dur en climat semi-aride tunisien est étudiée afin de disposer de références permettant le diagnostic de facteurs limitants au champ. On teste sur blé dur les relations entre composantes du rendement établies sur blé tendre en climat tempéré. En conditions où seuls la température et le rayonnement intercepté sont limitants, on obtient, sur blé dur, des relations analogues à celles établies sur blé tendre. Le paramétrage de ces relations est ici proposé. Le comportement du blé dur en conditions variables de nutrition azotée et hydrique au cours de 2 années de climat contrasté est étudié en utilisant les modèles préalables comme outils de diagnostic. Dans tous les cas, la principale composante liée au rendement est le nombre de grains par m2, qui dépend des conditions de croissance et de développement pendant la phase semis-floraison. La composante «poids d'un grain» est cependant affectée par les conditions d'alimentation hydrique, à travers la durée de la phase de remplissage du grain. On met en évidence en année humide l'influence du fractionnement de l'azote apporté sur plusieurs composantes du rendement. Une première formulation de références techniques sur la fertilisation azotée en conditions hydriques favorables est proposée et discutée.Analysis of yield components to diagnose limiting factors of durum wheat yield in semi-arid conditions: relationships under various water and nitrogen supplies. We studied the yield components of durum wheat (Triticum durum Desf) under semi-arid conditions in Tunisia (fig 1). The relationships between several yield components were established in conditions where nitrogen and water were unlikely to be limiting. The level of each component was fitted to that of components determined during previous periods of the crop cycle. Resulting relationships were considered as describing the maximum values of each component. They were plotted together with coupled values of components observed in conditions where water or nitrogen could be limiting. This allowed diagnosis of the effects of varying levels of nitrogen and water supplies on each yield component. The experiments were carried out in two soils ("Tell" and "Hamri", see table II) and several levels of nitrogen fertilization (fig 2), for two years with contrasting rainfall. The relationships between yield components, observed in the wet year and for high levels of nitrogen supply had similar patterns compared with those established for wheat grown in temperate regions (table I). However, the values of fitted parameters (table III) were appreciably different. In "Tell" soil, the maximum levels of all yield components were reached during the wet year for nitrogen fertilization as low as 60 kg ha-1, applied at tillering and beginning of the stem elongation; in "Hamri" soil, the maximum levels could not be reached, even for a total nitrogen amount of 100 kg ha-1; yield components had very low levels during the dry year in the two soils, with no appreciable effect of fertilization (table IV). In both dry and wet years, yields correlated better with the number of kernels per m2 (fig 3) than with the kernel weight. This suggests that pre-anthesis environmental conditions had a overriding effect on yields (figs 4 and 5). The observed range of kernel weight was not large enough to induce high variations in yield, in spite of the wide range of water and nitrogen supply. We used these results to propose a way of deciding nitrogen fertilization in relationship with yield objective in wet conditions (table V)