Grain amaranths (Amaranthus spp.) are high protein content and protein quality pseudo-cereal crops whose favorable nutritional profile belies their potential to alleviate nutrition and food insecurity in developing countries. Grain amaranth was introduced as a nutrient dense food into the Kamuli District, eastern Uganda, in 2006. However, initial analysis of protein content of amaranth grain pooled from farms in the Kamuli District indicated that protein levels ranged from 11.7% to 12.5%, lower than the average value of 15% found in the literature. Based on previous surveys of amaranth production practices in the area, this study was designed to determine: 1) variability of amaranth grain yields and protein content between farms; 2) variability of amaranth grain yields and protein content between varieties; and 3) the effects of soil physical and chemical properties, and the use of organic soil amendments, on amaranth grain yields and protein content. On-station and on-farm trials were conducted to determine the effects of organic soil amendments on amaranth grain yield and protein content. The on-station trials were conducted during 2009 in Wakiso District in south-central Uganda, to test effects of poultry manure and composted manure, while on-farm trials took place on ten farms during the short rainy season of 2009 in Kamuli District to determine the effects of cattle manure on the aforementioned parameters. On-station grain amaranth trials were conducted twice, during both the dry and short rainy seasons, and tested the effect of poultry manure and composted manure applied at 0, 1, 1.5, and 3 ton ha^-1 on amaranth varieties “cream”, “golden” and ‘Plainsman’.  There were no significant differences between amendment treatments for either trial, however, mean grain yields for the rainy season were higher at 1886 kg ha^-1 compared to 1110 kg ha^-1 for the dry season. Concerning varietal differences, yields for “cream” and “golden” varieties were significantly greater than those for ‘Plainsman’ during the dry season, whereas in the rainy season “cream” yields were significantly greater than those for “golden” and ‘Plainsman’. Amaranth grain was pooled across all treatments and varieties to determine a protein content of 14.5% and 15.1% for the dry and rainy seasons, respectively. For the on-farm trials, yields were lower than in the on-station trials and were significantly different between farms. Application of cattle manure provided a significant yield increase. While there were no significant differences between varieties, amaranth grain protein content was significantly different between farms.  Average protein content of 14% across treatments and varieties revealed a greater amaranth protein content than previously reported for Kamuli District.