Growth, development and nutritional value of amaranthus tricolor L. as affected by salinity and harvesting procedure

Abstract

Low crop productivity in arid and semi-arid regions is a problem caused by water stress as well as associated high levels of soil and water salinity. An increased demand for salt tolerant crops is experienced in these regions. Amaranth is a glycophyte and C4 dicotyledonous crop, well adapted to arid and semi-arid regions. Previous studies on the physiological response of salt-stressed amaranths have indicated that this crop is salt tolerant. As vegetable, amaranths can be harvested by uprooting and by topping. The most common harvesting method is by topping, allowing repeated harvesting. When harvested by topping, the cutting height is an important parameter that may be manipulated to optimise growth rates. In this study, plants were exposed to different salt stress levels and harvesting procedures while yield and quality of Amaranthus tricolor were investigated. Nutrient solutions at four different electrical conducti vi ty (EC) levels were used to fertigate the plants. At high EC levels (4 mS cm-l and 8 mS cm-lj, the length and diameter of main stems, internode lengths, stem weights as well as root weights were reduced, especially with a longer growth period. However, the shoot: root ratio and leaf protein yields increased and flowering was delayed. The best leaf yield was obtained where plants were fertigated at an EC of 4 mS cm-l for 45 days. The cutting height did not affect leaf yield, growth rates and leaf protein yield in plants fertigated at EC levels of 1, 2 and 4 mS cm-l. At an EC of 8 mS cm-l, the growth rate recovered to a value similar to that of plants fertigated with an EC of 2 mS cmonly where plants were topped at 25%. With this less destructive cutting height (topped at 25%), leaf yields, growth rates and ·leaf calcium and protein yields at an EC of 8 mS cm" were superior to that of plants topped at 50%. In plants topped at 25%, the recovered growth rates at EC 8 mS cm-l was probably due to more photosynthetic active tissue left after cuttings, resulting in the accumulation of compatible solutes for osmotic adjustment.