Bio-organic composite manures for sustainable yield and quality of amaranth (Amaranthus tricolor)

An experiment was conducted during 2009–2011 at Vellayani, Thiruvananthapuram, Kerala, to study the effect of bio-organic composite manures along with microbial consortium on yield and quality of amaranth (Amaranthus tricolor L.). Organic sources used for the preparation of bio-organic composite manures were coir pith compost, poultry manure, neem-cake, groundnut cake, ash, rock dust and microbial consortium. Composite organic manures having at least 3% N and N: K ratio of 1: 0.5 was selected for further study. Five mixtures coir pith compost (50 g) + groundnut cake (35 g) + ash (15 g), poultry manure (50 g) + groundnut cake (30 g) + rock dust (20 g), coir pith compost (50 g) + groundnut cake (36 g) + rock dust (13 g) + microbial consortium (1 g), coir pith compost (50 g) + groundnut cake (35 g) + ash (14 g) + microbial consortium (1 g) and poultry manure (50 g) + groundnut cake (30 g) + rock dust (19 g) + microbial consortium (1 g) satisfied the selection criteria and and were identified for the field investigation. The results showed that quality attributes such as vitamin C, oxalate and nitrate content as well as nutrient uptake were found to be the highest for bio-organic composite manure-treated plants compared to the other treatments. But the beta-carotene content was the highest for the Kerala Agricultural University Package of Practices recommendation (100: 50: 50 kg/ha N: P₂O₅: K₂O). Available nutrient content of soil varied significantly among treatments. Application of Kerala Agricultural University Adhoc Organic Package of Practice (Cow's urine @ 500 litres/ha) recorded the maximum available N content; poultry manure (50 g) + groundnut cake (30 g) + rock dust (19 g) + microbial consortium (1 g) recorded the maximum available P content. The highest available K content was recorded in Kerala Agricultural University Package of Practice recommendation (100: 50: 50 kg/ha N: P₂O₅: K₂O) and the control plot recorded highest organic carbon content. Among the treatments, the maximum yield of 12.76 t/ha was obtained from poultry manure (50 g) + groundnut cake (30 g) + rock dust (19 g) + microbial consortium (1 g) and it was on a par with coir pith compost (50 g) + groundnut cake (35 g) + ash (15 g) (12.48 t/ha) and poultry manure (50 g) + groundnut cake (30 g) + rock dust (20 g) (11.65 t/ha). The quality, nutrient uptake and yield of amaranth were found to be better with application of bio-organic composite manures than Kerala Agricultural University Package of Practices.