Amino compounds in poultry litter, litter-amended soil and plants
Amino compounds (AC) generally constitute the bulk of N in soil, so understanding their cycling is critical for efficient N use in crop production. In this work, we quantified 19 amino acids and two amino sugars in 23 poultry litters (PL), five pasture soils with different PL application histories, and the grass grown on these pastures. Concentration of AC-N averaged 37.0 mg g-1 dry matter(DM) for the 23 PL samples, which represented approximately 76% of their total N. Pasture soils had received annual PL applications for 0, 5, 10, 15, and 20 years at rates of 0, 2.27, 2.27, 3.63, and 1.36 Mg ha-1 yr-1, respectively. Highest levels of AC-N were observed in soils receiving 10- and 15-yr PL, which implied that both freshly applied and residual PL contributed tosoil AC-N. However, the proportion of total soil N comprised of AC-N decreased with PL application, with AC-N accounting for 97% of total N in the control pasture soil, but only 40% insoils receiving PL for 20 years. Plants harvested from the control pasture field contained the least abundant AC-N (10.5 mg g-1 DM). Plant leaves harvested from the pasture field with 5-year PL application contained the greatest AC-N (23.7 mg g-1 DM). It is clear that additional research is needed for understanding the roles and transformations of amino compounds in soil N dynamics and plant N uptake in PL amended soils.