Comparative response of a day-neutral and photoperiod-sensitive sorghum to delayed sowing or transplanting

Soil moisture deficit frequently occurs at the onset of the growing season and may cause crop failure. Resowing with early maturing varieties has often been the only alternative, besides transplanting. To assess the relative efficiency of the two rescue methods two sorghum (Sorghum bicolor [L.] Moench) cultivars, 'IRAT204' (day-neutral) and 'Nazongala' (photoperiod-sensitive), were grown in seven drought-prone environments in Western Africa. Grain yield of both cultivars was reduced by delayed sowing or transplanting at all environments. However, transplanting had less depressive effects than late sowing for both cultivars. Yield reduction was lowest when transplanting or resowing was done not later than two weeks from normal sowing time. Compensation levels were higher with the cultivar 'IRAT204' than with 'Nazongala'. While transplanting could contribute to partial yield loss recovery under erratic rainfall environments, it should not be considered as an option beyond four weeks from the normal sowing dates with day-neutral cultivars, due to their lack of phenological plasticity. Les deficits hydriques interviennent frequemment en debut d'hivernage et causent souvent des manques a la levee. En dehors du repiquage, le seul recours des paysans est de resemer avec des varietes plus precoces. En vue de comparer l'efficacite relative des deux methodes de sauvetage, deux varietes de sorgho (Sorghum bicolor [L.] Moench), 'IRAT204' (non photosensible) et 'Nazongala' (photosensible), ont ete evaluees dans sept sites en Afrique de l'Ouest. Les rendements obtenus avec le resemis ou le repiquage ont ete certes moins eleves que ceux resultant du semis a la date optimale, mais le niveau de compensation a ete plus important avec le repiquage, particulierement lorsqu'il avait ete fait au plus tard deux semaines apres la date normale de semis. Les taux de compensation partielle de rendement ont ete plus eleves chez 'IRAT204' que chez 'Nazongala'. Bien que le repiquage puisse contribuer a une reduction des pertes en zones de pluviometrie erratique, il est deconseille au-dela de quatre semaines apres la date normale de semis, notamment pour les varietes non photosensibles, du fait de leur manque de plasticite phenologique.