Grain yield and its components study and their association with normalized difference vegetation index (NDVI) under terminal water deficit and well-irrigated conditions in wheat (Triticum durum Desf. and Triticum aestivum L.)

Six genotype of Triticum aestivum L. in 1991 and one genotype of Triticum durum Desf. and three of T. aestivum L. in 1992 were studied under different water regimes: full irrigation (R1), mild water stress (R3) and severe water stress (R2) at Magneraud (France). Traits evaluated were grain yield and its components, stress susceptibility index (SSI) and normalized difference vegetation index (NDVI). The analysis of variance revealed significant differences between regimes and among the cultivars for all traits except between regimes for thousand grains weight in 1991. The regime × variety interaction was significant for grain yield, thousand grains weight and NDVI in 1992 and for grain yield in 1991. For all traits, durum wheat (T. durum Desf.) has higher reduction in the two water stress than the common wheat (T. aestivum L.). Correlations studies revealed that grain yield, grains number/m², thousand grains weight and NDVI were associated with each other except for correlations between thousand grains weight on one hand and grain yield (1992) and grains number/m² (1991) on the other hand. 51.55, 27.88, 4.12% (1991) and 75, 43 and 20.2% (1992) of grain yield, grains/m² and thousand grains weight variability, respectively were explained by means NDVI variability. The grain yield and grains number/m² could be predicted using a single regression with NDVI.Keywords: Grain yield, grain yield components, NDVI, durum wheat and bread wheat

Maximisation of limited amount of water : forecasting and irrigation scheduling : application to a case of grain sorghum

Water and irrigation equipment are generally devoted to crops with high water requirements whereas it is possible to improve irrigation efficiency by supplementary irrigation on certain other crops. However, this type of irrigation is difficult to realize because of the necessity to choose first the level of water stress acceptable according to the crop phenology and then to determine when this occurs. The approach proposed in this study consists of foreseeing the effect of reduction of water supply using a crop yield model which takes into account the sensitive periods of the crop cycle to water stress. By using the Water Balance Model (WBM) coupled with crop yield function, it is possible to maximize the efficiency of a given volume of water on the basis of climatic series. This methodology is applied to the case of grain Sorghum in Mediterranean context, after calibration and validation on experimental data. A study based on climatic series of 21 years gives at the beginning of the crop cycle forecasting irrigation calendar and/or simple rules for irrigation. For the farmers who expect a decision making tool, the model can provide in real time application the crop water status and the yield prediction. In its adaptive version, the model can be updated, if necessary, by incorporating infra-red measurements. / Il est habituel de réserver l'eau et le matériel d'irrigation aux cultures avec des besoins en eau élevés alors qu'il est possible d'obtenir une meilleure efficience de l'eau en réalisant des irrigations de complément sur certaines cultures. Cependant ce type d'irrigation est difficile à conduire car il faut connaître à la fois le niveau de stress acceptable pour un stade phénologique donné et déterminer la date à laquelle il est atteint. L'approche proposée dans cette étude consiste à prévoir l'effet d'un déficit en eau à partir d'un modèle de rendement prenant en compte la sensibilité des différentes phases phénologiques au stress hydrique. En utilisant un modèle de bilan hydrique (WBM) couplé à une fonction de rendement sur des séries climatiques, il est alors possible de maximiser l'efficience d'un volume donné d'eau. Cette méthodologie est utilisée pour le cas du sorgho grain en région méditerranéenne après calage et validation du modèle. Un calendrier prévisionnel des irrigations est établi à partir d'une série climatique de 21 ans. Pour les irrigants qui le souhaitent, le modèle peut fournir en temps réel l'état de la culture et le rendement prévisionnel. Le modèle peut alors être recalé à partir de mesures de thermométrie infra-rouge