Long-Term Crop and Soil Response to Biosolids Applications in Dryland Wheat

Abstract

Biosolids have the potential to improve degraded soils in grain- fallow rotations. The objectives were to determine if repeated biosolids applications in wheat (Triticum aestivum L.)-fallow could supply adequate but not excessive N for grain production and increase soil C without creating a high risk of P loss. A replicated on-farm experiment was established in 1994 in central Washington, comparing anaerobically digested biosolids with anhydrous NH3 and a zero-N control. Biosolids were applied at 5, 7, and 9 Mg ha-1 every fourth year through 2010 and incorporated 10 cm deep, while anhydrous NH3 plots received 56 kg ha-1 N every second year. Soil NO3-N was nearly always <10 mg N kg-1 soil. Medium and high biosolids rates significantly increased bacteria/fungi ratios, Gram-negative bacteria, and anaerobic bacteria markers compared with anhydrous NH3. Biosolids can be an agronomically and environmentally sound management practice in wheat-fallow systems.