Aerated chicken, cow, and turkey manure extracts differentially affect lettuce and kale yield in hydroponics

Manure extracts possess great potential as alternate inorganic fertilizers. However, limited information exists on how manure influences plant growth. This study’s aim was to determine the impact of aerated manure extracts on romaine lettuce (Lactuca sativa var. longifolia) and Russian kale (Brassica napus var. ‘Red Russian’) in hydroponic systems. Chicken, cow, and turkey manure extract solutions (10, 25, and 50 g/L manure) were compared to a control (Hoagland) solution for lettuce and kale grown in an ebb and flow hydroponic system. The aboveground dry mass of lettuce grown in a 50 g/L turkey manure extract solution was greater than that of the control. The largest aboveground wet mass for kale occurred with the control. Nutrient analyses of all manure extract solutions showed a 29%–79% higher concentration of NH4–N and higher total nitrogen than the control. Principal component analysis of the nutrient solutions identified six nutrients that should be monitored to maximize plant yield when using manure extracts in hydroponics: NO3−, NH4+, Ca, Mg, Mn, and Na. Healthy lettuce and kale plants were grown in turkey manure extract solution (50 g/L). However, reduced aboveground wet and dry mass were recorded for both plants in chicken and cow manure extract solutions compared to the control. NH4+ toxicity likely killed all plants grown in chicken extract (50 g/L). Apart from NH4+ and P, all nutrients were below suggested concentrations suggested for lettuce growth. A combined manure/mineral fertilizer may be necessary to optimize hydroponic solutions.