Agronomic response of sorghum varieties to nitrogen management – Terry Hie Hie 2014–15

Abstract

Key findings • Although plant available water (PAW) at sowing was ~47 mm (0–120 cm), timely in-crop rainfall of 257 mm improved yield potential. • If yield and subsequently fertiliser decisions were made on PAW at sowing and a low input approach to nitrogen (N) application was taken, as per the nil treatment in this experiment (42 kg/ha of Granulock Z), 0.9 t/ha or 20% of yield potential would have been lost, compared with the optimum N response rate (120 kg N/ha). • Significantly, even at modest levels of N application (e.g. 40–80 kg N/ha), grain yield was increased by 0.56 t/ha or 13% over the nil N treatment. • Although maximum yield was achieved at 11.1% grain protein content (GPC), the rate of grain yield increase per unit of additional N declined at GPC >10%. Importantly, results from this experiment did show that yield was compromised by N deficiency when GPC was <9%. • Results from this experiment highlight the need to consider yield potential in terms of targeted yields and hence N requirements. Importantly, if N inputs are limited then yield potential can be negatively affected.