Use of zeolite with alum and PAC amendments to mitigate runoff losses of P,N and suspended solids from agricultural wastes applied to grassed soils

Diffuse pollutant losses containing phosphorus (P), nitrogen (N), and suspended solids (SS) can occur when agricultural wastes are applied to soil. This study aimed to mitigate P, N, and SS losses in runoff from grassed soils, onto which three types of agricultural wastes (dairy slurry, pig slurry, and dairy-soiled water [DSW]), were applied by combining amendments of either zeolite and polyaluminum chloride (PAC) with dairy and pig slurries or zeolite and alum with DSW. Four treatments were investigated in rainfall simulation studies: (i) control soil, (ii) agricultural wastes, (iii) dairy and pig slurries amended with PAC and DSW amended with alum, and (iv) dairy and pig slurries amended with zeolite and PAC and DSW amended with zeolite and alum. Our data showed that combined amendments of zeolite and PAC applied to dairy and pig slurries reduced total P (TP) in runoff by 87 and 81%, respectively, compared with unamended slurries. A combined amendment of zeolite and alum applied to DSW reduced TP in runoff by 50% compared with unamended DSW. The corresponding reductions in total N (TN) were 56% for dairy slurry and 45% for both pig slurry and DSW. Use of combined amendments reduced SS in runoff by 73 and 44% for dairy and pig slurries and 25% for DSW compared with unamended controls, but these results were not significantly different from those using chemical amendments only. The findings of this study are that combined amendments of zeolite and either PAC or alum reduce TP and TN losses in runoff to a greater extent than the use of single PAC or alum amendments and are most effective when used with dairy slurry and pig slurry but less effective when used with DSW.