Iron toxicity is a widespread nutrient disorder in lowland rice, notably in West Africa. It occurs in irrigated or rain‐fed rice crops when the soil contains excessive amounts of iron. Associated with leaf discoloration symptoms (bronzing), this excessive iron uptake causes poor growth and tillering and leads to severe yield reductions. Field experiments were carried out in West Africa from 1994 to 1998 at two sites with high iron toxicity and one non‐toxic site to assess the effects of iron toxicity on rice cropping and evaluate the tolerance of promising rice cultivars available in West Africa. To estimate yield losses caused by iron toxicity, the yield potential was simulated using the ORYZA‐S rice growth and yield model. Based on the potential yield, the yield loss in an iron‐toxic site is the combination of the yield gap caused by unknown site factors and the yield gap caused by iron toxicity. Compared to the referential yield obtained in a non‐iron‐toxic site, iron toxicity reduced rice yields by 16–78 % (mean 43 %). The extent of the yield loss depended on rice cultivar, iron toxicity intensity and crop management strategy (water control and mineral fertilisation). A strong correlation obtained between yield and the iron toxicity score, based on visual symptoms indicated an approx. 400 kg ha−1 yield loss for each visual score point increase. The high genetic variability in iron toxicity tolerance and close correlation between leaf symptom score and grain yield between rice genotypes provide a good basis for breeding varieties that can produce higher yields under iron‐toxic conditions.

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More than 60% of phosphorus (P) taken up by rice (Oryza spp.) is accumulated in the grains at harvest and hence exported from fields, leading to a continuous removal of P. If P removed from fields is not replaced by P inputs then soil P stocks decline, with consequences for subsequent crops. Breeding rice genotypes with a low concentration of P in the grains could be a strategy to reduce maintenance fertilizer needs and slow soil P depletion in low input systems. This study aimed to assess variation in grain P concentrations among rice genotypes across diverse environments and evaluate the implications for field P balances at various grain yield levels. Multi-location screening experiments were conducted at different sites across Africa and Asia and yield components and grain P concentrations were determined at harvest. Genotypic variation in grain P concentration was evaluated while considering differences in P supply and grain yield using cluster analysis to group environments and boundary line analysis to determine minimum grain P concentrations at various yield levels. Average grain P concentrations across genotypes varied almost 3-fold among environments, from 1.4 to 3.9 mg g−1. Minimum grain P concentrations associated with grain yields of 150, 300, and 500 g m−2 varied between 1.2 and 1.7, 1.3 and 1.8, and 1.7 and 2.2 mg g−1 among genotypes respectively. Two genotypes, Santhi Sufaid and DJ123, were identified as potential donors for breeding for low grain P concentration. Improvements in P balances that could be achieved by exploiting this genotypic variation are in the range of less than 0.10 g P m−2 (1 kg P ha−1) in low yielding systems, and 0.15–0.50 g P m−2 (1.5–5.0 kg P ha−1) in higher yielding systems. Improved crop management and alternative breeding approaches may be required to achieve larger reductions in grain P concentrations in rice.

Phosphorus deficiency is a major soil‐related constraint to upland rice (Oryza sativa L.) production in Sub‐Saharan Africa. Rice varieties adapted to low soil P and also respond well to added P fertilizer are needed. Simple and cost‐effective screening protocols could help to identify varieties with superior growth at the vegetative stage. This would be particularly useful in weed‐prone uplands where early vigor is an important trait. The objectives of this study were to (i) assess variation in aboveground biomass of 12 upland rice varieties, including the popular ‘NERICA’ varieties, with and without P supply using a double pot technique; (ii) examine if aboveground biomass measured using this technique can predict aboveground biomass at the vegetative stage under field conditions with and without P; and (iii) identify new donors for breeding for P deficiency tolerance. At 5 to 7 wk after sowing, aboveground biomass and root biomass were determined in pot and field experiments. In the pot experiment, there was significant varietal variation in aboveground biomass with and without P. Results from the pot experiment corresponded with varietal performance in the field experiments. ‘Mugdo’ generally produced the highest aboveground biomass with and without P across both experiments, followed by ‘DJ123’. Aboveground biomass without P relative to the biomass with P was consistently low in ‘Santhi Sufaid’ across both experiments. The double pot technique offers a promising, effective, and reliable approach for screening for P deficiency tolerance and Mudgo can be used as donor for improving early growth under P‐deficient soil conditions.

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