Biomass yield and phosphorus availability to wheat grown on high phosphorus soils amended with phosphate inactivating residues. II. Iron rich residue

Abstract

Reducing the environmental risk from soluble phosphorus (P) in long-term poultry manured fields can involve increased use of chemical soil amendments such as aluminum (Al), calcium (Ca), and iron (Fe). Iron salts have been proven effective in removing soluble P from wastewater and have been used to inactivate P in poultry litter and litter-amended soils. The potential for P deficiency in crops grown on Fe treated soils is of concern. A growth chamber experiment was conducted using Matapeake, Evesboro, and Woodstown soils with Mehlich 3 extractable P (M3-P) levels above 800 mg kg−1 in order to 1) determine the effects of a Fe-rich residue (IRR) on crop biomass yield and on plant P, Mn, and Fe contents, and 2) examine pH, electrical conductivity (EC), P, Mn, and Fe concentrations in soils after three cropping cycles with wheat. IRR was mixed with the soils at rates of 0, 10, 25, and 50 g kg−1 and incubated for seven weeks. Three crops of wheat (Triticum aestivum) were grown in succession. Biomass yield (BM) and tissue P concentrations were significantly reduced with the additions of IRR for all three soils, but the differences were much less at the 10 g kg−1 application rate than at the 25 and 50 g kg−1 rates. Biomass yield was 29% lower than the control at the 10 g kg−1 IRR rate compared to 74% lower at the 50 g kg−1 rate. Even though tissue P concentrations were reduced, levels were within the range considered sufficient for wheat growth for all treatments. The high Mn and DTPA-Fe in the IRR treatments increased tissue Mn and Fe concentrations, but the levels were below the concentration considered to be toxic to most crops. Water soluble P and M3-P concentrations were lowered with increased IRR application rate for each soil and correlated positively with tissue P for the three soils. DTPA extractable Mn concentrations in soil increased, but Fe concentrations decreased with increased IRR application, for the three soils. IRR treatments initially increased both pH and EC in the three soils, however, reductions in pH and EC values were found with subsequent cropping cycles. Further studies to identify and limit the negative impact of IRR on plant growth are needed before the materials should be considered for field application to sequester soluble P in high P soils.