Eco-physiological Responses of Amaranthus cruentus L. to Deficit Irrigation under Different NPK 20:10:10 Fertilization Rates

The aim of this research was to investigate the responses of Amaranthus cruentus L. to deficit irrigation under fertilization, in a 2 by 3 factorial experiment with two levels of irrigation (1.5 litre/week and 0.75 litre/week) corresponding to 2600 and 1300 mm/year respectively and three levels of NPK 20:10:10 (0, 138, 275 kg ha-1). This experiment was conducted in a screen house in Cameroon, and lasted for 12 weeks after the nursery phase. Growth parameters and chlorophyll fluorescence were measured weekly for 8 weeks. Destructive sampling was done at 12 WAT to determine biomass partitioning, water use efficiency and the root/shoot ratio. Data were analyzed for variance and relationships in the MINITAB Version 17 statistical package. Within each irrigation level, plant mass decreased as fertilizer rates decreased, while root: Shoot ratio increased instead. Plant mass expressed higher values at the higher irrigation levels while root: Shoot ratio was lower compared to that at lower irrigation levels. This shows a strategy for resource re-allocation to roots under both water and nutrient deficit. Harvest index was statistically similar across irrigation and fertilizer levels. Within the higher irrigation levels, WUE of plants decreased with a decrease in fertilizer rates but not for plants subjected to deficit irrigation. While chlorophyll fluorescence values differed significantly across treatments, all values were below 0.8, indicative of stress. Factor analysis showed that growth of A. cruentus was highly fertilizer-dependent, while chlorophyll fluorescence was irrigation-dependent. This suggest that fertilizer application is essential in ameliorating the effects of deficit irrigation, and will be essential in the production of this crop under deficit irrigation.