Nutrient Transport in Runoff from Feedlot Surfaces as Affected by Unconsolidated Surface Materials

Abstract

Beef cattle feedlots contain unconsolidated surface materials (USM) (loose manure pack) that accumulate within feedlot pens during a feeding cycle. The effects of varying amounts of USM on feedlot runoff water quality are not well defined. The objectives of this field investigation were to: a) compare nutrient transport in runoff from feedlot surfaces containing varying amounts of USM, b) determine if runoff nutrient transport is correlated to feedlot soil characteristics, and c) identify the effects of varying runoff rate on nutrient transport from feedlot surfaces containing varying amounts of USM. Simulated rainfall was applied to 0.75-m wide by 2-m long plots during three 30-min events. No significant (P < 0.05) differences in runoff water quality characteristics were found among the four treatments containing varying amounts of USM. Runoff measurements of PP, NH4-N, NO3-N and EC were each significantly correlated to six or more feedlot soil parameters. The NH4-N, TN, and NO3-N loads were all correlated to easily obtained soil EC measurements. The presence of USM at rates varying from 0 to 26.9 kg m-2 did not significantly affect any of the measured water quality parameters under varying flow rates. In contrast, each of the measured water quality parameters was significantly influenced by runoff rate. Thus, runoff rate and not the amount of USM on the feedlot surface is a critical variable influencing runoff water quality. Thus, runoff nutrient load from feedlot surfaces can be expected to increase significantly with down slope distance.