Short-Term Soil Responses to Biofeedstock Removal Under Dryland Cropping.

Data documenting crop residue removal effects on soil properties is limited for semiarid cropping systems.  In 2008, a Bioenergy Cropping Study (BCS) was initiated near Mandan, North Dakota, USA to investigate residue removal effects on crop production, environmental outcomes, and economic returns.  In this investigation, we sought to quantify short-term (3 yr) soil responses to applied BCS treatments, which included three crop sequences [Spring wheat (Triticum aestivum L.)-Dry pea (Pisum sativum L.), SW-P; Spring wheat-Dry pea-Corn (Zea mays L.), WPC; Spring wheat-Pea/Cover crop mixture; WP/CCM] and four levels of residue removal (No biomass removal, NONE; Wheat straw mechanically harvested, WHARV; Wheat straw, pea residue, corn stover mechanically harvested, ALLHARV; Wheat straw, pea residue, corn stover grazed, ALLGRZ).  Treatment effects on soil properties were mostly concentrated near the soil surface.  Soil bulk density (0-5 cm) was significantly greater in ALLGRZ (1.25 Mg m^-3) compared to other residue removal treatments (Mean = 1.16 Mg m^-3), as was extractable NH₄-N and total N.  Significantly lower soil pH was observed at 0-5 cm for ALLHARV (5.46) compared to ALLGRZ and NONE (Mean = 5.66).  Soil organic C and particulate organic matter C were not affected by residue removal treatments at any depth.  Among crop sequences, soil bulk density (0-10 cm) and pH (0-20 cm) were significantly lower in WPC than WP and WP/CCM.  Particulate organic matter C at 0-5 cm was greater under WPC and WP/CCM (Mean = 3147 kg C ha^-1) than WP (2570 kg C ha^-1).  Despite the relatively short duration of BCS treatments, changes in soil condition were observed in this investigation.  Continued monitoring is necessary to discern the trajectory in soil properties and associated implications to soil function and system sustainability.