Dry matter accumulation and post-silking N economy of ‘stay-green’ maize (Zea mays L.) hybrids

•We grew four maize hybrids with different ‘stay-green’ ratings and applied different nitrogen (N) levels.•The ‘stay green’ trait was exhibited in the maintenance of green leaf area.•Hybrids of low ‘stay green’ rating remobilized more of their pre-silking leaf N to grain.•Grain N content was lower in hybrids with a high ‘stay green’ rating.

The decline in dry matter accumulation in maize (Zea mays L.) during kernel filling, as N is remobilised, has elicited interest in the evaluation of traits to sustain leaf dry matter during this period. This study at Lincoln University, New Zealand, examined the post-silking nitrogen economy of maize hybrids that differed in their ‘stay-green’ rating (sgr). The objective was to quantify contributions to dry matter and kernel yield that accrue from the ‘stay-green’ trait and also understand its physiological basis. The response of ‘P39K38’ (sgr 6), ‘P38V12’ (sgr 7), ‘P38F70’ (sgr 8), and ‘P38G43’ (sgr 9) to 0 or 270 kg nitrogen (N) ha−1 and nil or full irrigation was quantified in 2008/09. Only ‘P39K38’ (sgr 6), and ‘P38G43’ (sgr 9) were examined in 2009/10 when all crops were fully irrigated. Total accumulated dry matter and N content were determined from sequential harvests. In 2008/09 total accumulated dry matter did not differ (P = 0.509) amongst the hybrids but ‘P39K38’ (sgr 6) yielded 2 t ha−1 more (P = 0.013) than ‘P38G43’ (sgr 9) in 2009/10. Total crop N did not differ among the hybrids at silking in both seasons. However, throughout kernel filling, the lower ‘stay-green’ rated hybrids remobilised more N from their leaves (∼20 kg N ha−1 at physiological maturity in 2008/09). In both seasons, the lower ‘stay-green’ rated hybrids also had more N accumulated in their kernels. The expression of the ‘stay-green’ trait was shown by the retention of more leaf N with no consequence kernel yield, but a decrease in kernel N content.