Meta-Analyses of Biosolids Effect in Dryland Wheat Agroecosystems

Land application to cropping systems is USEPA's preferred method of recycling biosolids. Determination of biosolids effect size through meta-analyses from two decades of field-location research at three sites should answer the question: Does 20 yr of biosolids application affect dryland wheat ( L.) grain production, grain nutrient concentrations, and soil elemental extractability compared with equivalent rates of commercial N fertilizer? At two sites, biennial biosolids application rates to a wheat-fallow (WF) rotation were up to 11.2 dry Mg ha and up to 112 kg commercial N fertilizer ha, whereas rates at the third location varied to match soil-test information. Crop rotations included WF and wheat-corn ( L.)-fallow. We completed meta-analyses of biosolids effects compared with N fertilizer on wheat yield, grain protein, grain total, and soil ammonium bicarbonate-diethylenetriaminepentaacetic acid (ABDTPA)-extractable P, Zn, Cu, Fe, and Ni concentrations at the aforementioned sites from 1993 through 2013. Results showed that biosolids produced greater grain P and Zn at one site. Biosolids rates at two sites resulted in greater grain Zn and ABDTPA P, Zn, Cu, and Fe. Meta-analyses tests for heterogeneity indicated that the variance for all sites and rates could be explained as consistent across treatments, whereas the test for the 20 yr showed that heterogeneity was large and other factors affected the variance (e.g., climatic variability between years). Meta-analysis showed the practical effect of biosolids over a 20-yr study and demonstrated that the primary biosolids effect was an improvement in Zn availability to wheat.