Abstract
Soybean [Glycine max (L.) Merr.] grain yield is closely associated with the level of optimal nitrogen (N) supply, especially during the reproductive stages. Foliar fertilization with low rates of N have been considered as a strategy for furnishing additional N and enhancing grain yields. Field studies using 15N tracer were conducted over two growing seasons to investigate the impact of foliar N fertilization on grain yield, plant N content, the amount of N derived from fertilizer (NDFF) and N recovery efficiency (NRE). Four foliar N rates (0, 1300, 2600 and 3900 g ha−1) were supplied by two equal split applications at the R1 and R3 stages. Foliar N fertilization of soybean canopies did not affect grain yield, grain N content, shoot N content nor plant N content. Total NDFF was increased from 0.7 to 2.0 kg ha−1 across the N rates. Nonetheless, NRE was unaffected by foliar N fertilization, which averaged 53 %. Soybean plants allocated the same amount of N fertilizer to both grains and shoots. No significant effects of low rate foliar N fertilization were registered on soybean grain yield nor plant N content, despite considerable N fertilizer recovery by plant organs.
Highlights
Foliar nitrogen (N) fertilization is an increasingly common practice in commercial grain soybean [Glycine max (L.) Merr.] production
Field studies using 15N tracer were conducted over two growing seasons to investigate the impact of foliar N fertilization on grain yield, plant N content, the amount of N derived from fertilizer (NDFF) and N recovery efficiency (NRE)
Plant N content and N internal efficiency (NIE) had similar responses to foliar N application, and while no difference was registered across rates, differences between years were significant for grain and plant N content
Summary
Foliar nitrogen (N) fertilization is an increasingly common practice in commercial grain soybean [Glycine max (L.) Merr.] production. Previous studies have shown grain yield increases resulting from foliar N fertilization (Vasilas et al, 1980; Blandino and Reyneri, 2009; Ranđelović et al, 2009; Jyothi et al, 2013; Khan et al, 2013). Using foliar N application during the pod-filling, Ikeda et al (1991) reported increased photosynthetic productivity in leaves and the export of photosynthates to the nodules for an extended length of time. In studies investigating foliar application effects on grain N concentrations, such concentrations increased between 0.2 % and 2.4 % (Ruske et al, 2003; Blandino and Reyneri, 2009; Mandić et al, 2015)
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