Evaluation of Poplar Trees Irrigated with Livestock Lagoon Wastewater

Abstract

Research conducted at Kansas State University evaluated the growth and nutrient utilization characteristics of poplar trees irrigated with livestock lagoon wastewater from May 2004 through June 2006. Poplar trees (eastern cottonwood; Populus deltoides Bartr. Ex Marsh.) were planted as dormant rooted cuttings on 19 May 2004 in a system of twelve lysimeter cells with three trees per cell. Irrigation treatments included lagoon water (LG), a blend of 50% lagoon and 50% freshwater (BL), and freshwater (FR). The lysimeters contained a silty loam soil with very low nutrient content at the start of the study, and the only nutrient applications the trees received was through the wastewater. Beginning in July 2004, weekly irrigation applications of 25 mm of the appropriate water treatment were applied to each lysimeter cell using a drip irrigation system. In order to accommodate different tree growth and water requirements in the second and third growing seasons, irrigation applications were scheduled using tensiometers at various depths. In 2005, trees showed signs of decline due to soil salinity build up in the BL and LG treatments. Freshwater leaching events and limited lagoon water applications were then scheduled for those treatments for the remainder of the study. The poplar trees showed a positive growth response to lagoon water applications. At the end of the study (June 2006), the LG treatment trees had an average height of 362 cm and trunk diameter of 65 mm, while the FR trees were significantly smaller with an average height of 281 cm and an average trunk diameter of 34 mm. Furthermore, the lagoon treatments (BL and LG) resulted in three to five times as much leaf biomass and three to four times as much woody biomass as the FR treatment. In general, soil levels of NO3-N, NH4-N, P2O5, and EC were elevated in the lagoon water treatments. Leaf tissue %N was also higher from trees that received lagoon water. Trees receiving lagoon water irrigation also required more irrigation water than the trees receiving only freshwater irrigation.