Effect of organic and in organic fertilisers on yield and quality of amaranth in sub-Saharan Africa

Abstract

This study was designed to evaluate the influence of manure and mineral fertilization on yield, Kjeldahl nitrogen (as protein equivalents), Vitamin C and nitrate accumulation in Amaranthus hypochondriacus. The vegetables were produced in field trials, set up in the University of Nairobi, Kenya, during the long rains period between March and May in 2007 and 2008 using diammonium phosphate (DAP; 20, 40 and 60 kg N ha-1) and manure; 40 kg N kg ha-1,) and the yield, Kjeldahl nitrogen (K-N; a proxy for protein content), vitamin C and nitrate levels were measured. The manure treatment produced little increase in productivity though it increased K-N levels. The DAP treatments produced increases in yield, but these saturated at 40 kg N ha -1. The K-N content of the leaves was high, ranging from 2.5 % to just over 4 %, and, broadly, increased with fertiliser application though the variation between the treatments was lower than that for yields. Nitrate levels, however, also increased with DAP fertilisation, resulting in an increase in the nitrate:K-N at high DAP applications, especially in younger plants. There were no clear correlations between ascorbic acid content and K-N. Nonetheless, the plants grown under different fertilisation regimes can be placed into three broad groups; those characterised with low to moderate K-N contents and low to high ascorbic acid contents, moderate to high K-N and low to high ascorbic acid content, and lastly high K-N and low ascorbic contents. Therefore, the growth environment of amaranth, can have a major impact not only on the productivity of the crop but its nutritional value. In this respect the mineral nutrient supply to the crop is of particular importance.