Boron contents and isotopic compositions of hog manure, selected fertilizers, and water in Minnesota

Boron-isotope (delta(11)B) values may be useful as surrogate tracers of contaminants and indicators of water mixing in agricultural settings. This paper characterizes the B contents and isotopic compositions of hog manure and selected fertilizers, and presents delta(11)B data for ground and surface water from two agricultural areas, Boron concentrations in dry hog manure averaged 61 mg/kg and in commercial fertilizers ranged from below detection limits in some brands of ammonium nitrate and urea to 382 mg/kg in magnesium sulfate, Values of delta(11)B of untreated hog manure ranged from 7.2 to 11.2 parts per thousand and of N fertilizers were -2.0 to 0.7 parts per thousand. In 22 groundwater samples from a sand-plain aquifer in east-central Minnesota, B concentrations averaged 0.04 mg/L and delta(11)B values ranged from 2.3 to 41.5 parts per thousand. Groundwater beneath a hog feedlot and a cultivated field where hog manure was applied had B-isotope compositions consistent with the water containing hog-manure leachate, In a 775-km(2) watershed with silty-loam soils in southcentral Minnesota: 18 samples of subsurface drainage from corn (Zea mays L.) and soybean (Glycine maw L. Merr.) fields had average B concentrations of 0.06 mg/L and delta(11)B values of 5.3 to 15.1 parts per thousand; 27 stream samples had average B concentrations of 0.05 mg/L and delta(11)B values of 1.0 to 19.0 parts per thousand; and eight groundwater samples had average B concentrations of 0.09 mg/L and delta(11)B values of -0.3 to 23.0 parts per thousand. Values of delta(11)B and B concentrations, when plotted against one another, define a curved miro ng trend that suggests subsurface drainage and stream water contain mixtures of B From shallow and deep groundwater.