Effect of timing and method of nitrogen application on rind colour, fruit size, internal fruit quality and yield of ‘Mihowase Satsuma’ mandarin (Citrus unshiu Marc.)

Abstract

Early rind colour development is a major problem in the production of early-maturing ‘Mihowase Satsuma’ mandarin (Citrus unshiu Marc.) in the Western Cape, South Africa. The effect of different combinations of soil- applied limestone ammonium nitrate and foliar-applied low-biuret urea on rind colour, fruit size, internal fruit quality and yield of ‘Mihowase Satsuma’ mandarin on ‘Troyer’ citrange [C. sinensis (L.) Osbeck × Poncirus trifoliata (L.) Raf.] rootstock was evaluated. This study was carried out over four consecutive seasons in Stellenbosch, South Africa (33°56'S, 18°51'E; 119 m.a.s.l.; Mediterranean-type climate). Despite a wide range in annual N application rate from 88 to 180 kg N-ha^-1 p.a., leaf N concentration never exceeded 2.2%, with no consistent differences in leaf N levels, rind colour, fruit size, internal fruit quality and yield among treatments. The current leaf N norms for ‘Satsuma’ mandarin may be too high, and an optimal leaf N content of 1.9 to 2.1% is suggested.