Influence of organic and mineral fertilization on germination, leaf nitrogen, nitrate accumulation and yield of vegetable amaranth

The influence of manure and diammonium phosphate (DAP) mineral fertilizer on germination, leaf nitrogen content, nitrate accumulation and yield of vegetable amaranth (Amaranthus hypochondriacus) was investigated. Field trials wereset up at the University of Nairobi Field Station at the Upper Kabete Campus during the long rains of March-May in 2007 and 2008. Trials werelaid out as complete randomized block design with four fertilization treatments: 20, 40, and 60 kg nitrogen (N) n«:' supplied byDAP (18:46:0), 40 kg N hn"!supplied by cattle manure and an unfertilized control variant. The vegetables were harvested at three maturity stages at 6, 7, and 8 weeks after planting. Results indicated that there were significant differences between treatments in germination percentage, leaf nitrogen content, nitrate accumulation and vegetable yield. Plants that received manure had a higher germination percentage than those that received the same amount of N supplied by the chemical fertilizer DAP. The yields generally increased from week 6 to week 8. The highest yield was recorded in plots receiving 40 kg N h«:' from DAP at eight weeks after planting. Plots that weresupplied with manure recordedthe lowestyield when compared to thefertilizer treated plots at all rates. Leaf nitrogen content increased with increasing rate of N but only when N was supplied byDAP fertilizer. The leaf nitrogen content decreased with increasing age of theplants. The leaf nitrate content increased with increase in DAP application rate. Results indicate that manure application produced quality vegetables in terms of low nitrate levels, but leaf nitrogen and vegetable yields werelow. DAP application effected higher yields, but the vegetables had high though acceptable nitrate levels. Keywords: amaranth, nitrogen, manure, yield, nitrate accumulation