Path Analyses of Grain P, Zn, Cu, Fe, and Ni in a Biosolids‐Amended Dryland Wheat Agroecosystem

Abstract

Land application of biosolids is an effective means of recycling plant nutrients and is the primary method of biosolids reuse endorsed by the USEPA. One issue concerning biosolids application is the extent of the contribution of biosolids-borne plant nutrients to the overall crop concentration and uptake or removal of these nutrients. We studied the effects of biosolids application on wheat ( L.) grain P, Zn, Cu, Fe, and Ni concentrations and uptake (removal) at two dryland agroecosystem sites from 1993 to 2014. We hypothesized that biosolids would have the greatest impact on wheat grain and uptake compared with ammonium bicarbonate-diethylenetriaminepentaacetic acid (AB-DTPA)-extractable nutrient levels, soil pH, or soil organic C concentrations. We used path analyses in combination with multiple linear regression to differentiate the direct, indirect, and total effects of cumulative biosolids applications, soil AB-DTPA, soil pH, and organic C. Biosolids rates, applied biennially from 1993 to 2014 at the beginning of a wheat-fallow rotation, were 0, 2.24, 4.48, 6.72, 8.96, and 11.2 Mg ha. None of the parameters had significant direct, indirect, or total effects on grain concentrations. Biosolids applications had the greatest positive direct impact compared with AB-DTPA levels, soil pH, or soil organic C on P, Zn, Fe, and Ni uptake (removal), whereas AB-DTPA had the greatest positive direct impact on Cu uptake. Soil AB-DTPA, pH, and organic C directly affected some grain concentrations and cumulative uptake, but no consistent trends were noted. This pathway approach allowed differentiation between causation and simple correlation for the effects of cumulative biosolids applications on wheat P, Zn, Cu, Fe, and Ni cumulative uptake but did not provide these same results for grain concentrations.

Agronomic impacts of new regulations governing land application of Class B biosolids in Florida

“…(2020) also reported that biosolids application increased bahiagrass tissue Mg and Zn concentrations by 12% and 21% compared to inorganic fertilizer, respectively. The increase in tissue Zn concentrations in response to biosolids application was also reported in long‐term (11‐ to 20‐year long) field experiments with wheat ( Triticum aestivum L.) (Barbarick et al., 1995, 2016). Increased tissue Cu concentration in response to biosolids application has been reported in a field study with bahiagrass (Adjei & Rechcigl, 2002) and in long‐term studies with wheat (Barbarick et al., 1995, 2016).…”

“…The increase in tissue Zn concentrations in response to biosolids application was also reported in long-term (11-to 20-year long) field experiments with wheat (Triticum aestivum L.) (Barbarick et al, 1995(Barbarick et al, , 2016. Increased tissue Cu concentration in response to biosolids application has been reported in a field study with bahiagrass (Adjei & Rechcigl, 2002) and in long-term studies with wheat (Barbarick et al, 1995(Barbarick et al, , 2016. In contrast to our data, previous studies demonstrated no difference between inorganic fertilizer and biosolids application on bahiagrass tissue Mg (Adjei & Rechcigl, 2002;Tiffany et al, 2001a).…”

“…In this context, biosolids can be a valuable resource to improve the sustainability of degraded pastures and to restore ecosystem functions such as availability of nutrients and food production. This study, along with a significant body of literature, has demonstrated that biosolids have considerable fertilizer value and can be an economical and sustainable alternative to commercial inorganic fertilizer (Adjei & Rechcigl, 2002;Barbarick et al, 2016;Ippolito et al, 2021;Mullen et al, 2005;Sigua et al, 2005;Tiffany et al, 2001a;2001b).…”

“…That means that if applied at equivalent rates, biosolids are expected to be less effective than inorganic fertilizer in improving forage productivity (Lu, Silveira, Vendramini et al., 2020; O'Connor et al., 2004). Biosolids treatment process is also expected to affect plant‐available nutrients (Silveira et al., 2019; Singh & Agrawal, 2008) and subsequent crop responses (Barbarick et al., 2016; Lu, Silveira, Vendramini et al., 2020). Limited P solubility in biosolids is mainly due to the addition of aluminum (Al) and iron (Fe) during the wastewater treatment process (Huang et al., 2007; Huang & Shenker, 2004).…”

The Clean Water Act and biosolids: A 45‐year chronological review of biosolids land application research in Colorado

“…• The extent of biosolids-borne plant nutrients to overall crop nutrient concentration, uptake, and ultimately off-site removal. Barbarick et al (2016) used pathway analysis, in combination with multiple linear regression, to identify the (in)direct and total effects of repeated biosolids applications (over a 20-yr period), soil extractable elements, soil pH, and organic C content on removal of P, Zn, Cu, Fe, and Ni in wheat grain. The authors noted that (a) the number of biosolids applications had the greatest positive effect on grain nutrient removal, and (b) AB-DTPA-extractable Cu content was positively correlated with plant Cu uptake.…”