Preliminary field study of soil TKN in a wastewater land application system

An accurate nitrogen mass balance is necessary when designing a municipal wastewater land application system in order to reduce the potential for nitrogen contamination of groundwater. Limited information on soil total Kjehldahl nitrogen (TKN) is available to estimate the TKN variance in the soil that can be used for calculating the nitrogen mass balance. This study investigated the soil TKN temporal variance at two different depth ranges within three different soil types irrigated with municipal wastewater effluent in a short-term at a long-term running site under field conditions. Three plots were chosen with each plot growing different plants and with different soil types in Lubbock, Texas, USA. Kruskal-Wallis one way analysis of variance on ranks and Mann-Whitney rank sum test were employed to compare the differences of medians of many groups of data and of two groups of data at p<0.05, respectively. The results show that there was no significant difference among the medians of monthly soil TKN in the depth of 46-61. cm for all three test plots. The risk for nitrogen leaching should be highly considered when the crop grown is alfalfa and during the winter season. Wheat and hay grazer rotation and Bermuda grass are better options to maintain a relatively stable soil TKN. The study calls on further and more detailed field investigations and to quantify the soil TKN at a municipal wastewater land application site in order for more accurate modeling, simulation and prediction of nitrogen leaching.