Phosphorus immobilization and soil aggregation in chemically amended poultry litter used in corn/soybean rotation

Excessive use of poultry litter (PL) on agricultural land is known to cause eutrophication of surface waters. Consequently, both poultry producers and PL users have to meet strict state and federal guidelines on litter storage and land application. This study examined the environmental benefits of adding lime, alum, ferrous sulfate, fly ash (FA), fluidized bed ash (FBA) and soil fix (SF) to PL for immobilizing excess phosphorus (P) while providing sufficient nutrients for proper growth of soybean [Glycine max (L.)] and corn [Zea mays (L.)] on a rotation. Amending PL with lime, alum, SF, FA and FBA significantly (p>0.05) increased corn and soybean yield. In contrast control plots that received a 10-10-10 (N-P2O5-K2) fertilizer showed lower yield and corn quality. Increased yield was observed when PL was amended with lime, alum and ferrous sulfate. Results from a soybean root, shoot, and nodule growth study indicated variability with respect to PL application and amendment use. Smaller size nodules were obtained with NPK fertilizer and PL plus lime treated plots, whereas PL with alum yielded fewer but larger nodules. Soil aggregation was significantly lower in soils treated with NPK compared to those treated with PL as indicated by water stable aggregation (WSA), mean aggregate diameter (MWD) and geometric mean of aggregate diameter (GMD) (p>0.05). Increased soil aggregation was a result of the combined effect of amendment and PL additions rather than PL alone. The amount of carbon (C) in soil aggregates was lowest with NPK and highest with PL treatments. In the presence of PL, alum and iron treatments showed higher capacities to store C and immobilize P in macro-aggregates (8 to 5 mm diameter). These results suggest that soil treatment with PL and chemical amendments, especially alum and ferrous sulfate, could result in improved crop yield, soil aggregation, carbon storage, and P immobilization.