AbstractThe oxalate content of napier grass and of pearl millet × napier grass interspecific hybrids was studied in plants grown in midsummer in the field and in a phytotron under three temperature regimes. The plants in the field were irrigated every 3, 7 or 14 days and given at each irrigation a heavy application of nitrogen, not less than 5 kg N ha−1 day−1. The plants in the phytotron were irrigated daily with a complete nutrient solution containing 200 mg l−1 of nitrogen.The highest total and soluble oxalate contents in the dry matter of field grown plants were 2·6 % and 1·3%, respectively. The oxalate status of the plant was not affected by the irrigation or N fertilisation. In contrast, plants grown in the phytotron accumulated as much as 4·4 % of total and 3·4% of soluble oxalates, and both decreased with advancing maturity irrespective of the temperature regime.The content of sodium + potassium in the dry matter was linearly correlated with oxalate content (r2 = 0·78) in the pooled data of all four experiments reported herein. There was no change in oxalate with N content above 2·0 % of the dry matter. Below that level oxalate increased Steeply with N content. However, in this range, N content is linearly correlated with (Na + K) content, and so its relation with oxalate is indirect.Oxalate levels in the leaves were higher than in the stems and decreased in both plant parts with advancing maturity. Only small differences in oxalates were found between the hybrids tested. Napier grass accumulated more oxalate in the stem than its F1 hybrid, both having higher concentrations in tounger stem internodes. NO differences in ozalate levels were found between the leaves of he parent grass and its hybridIt is concluded that a hazardous concentration of oxalate in millet × napier hybrids is unlikely even under intensive N fertilisation. Consequently, consideration of oxalate accumulation need not be a constraint in breeding for imporved hybrids of this grass.