UTILIZATION OF HIGH NITROGEN AND SWINE MANURE AMENDMENTS FOR CONTROL OF SOIL-BORNE DISEASES: EFFICACY AND MODE OF ACTION

摘要

Single applications of high nitrogen-containing organic amendments, such as meat and bone meal and soymeal, to sandy soils (0.5-2% w/w), controlled a spectrum of soil-borne plant diseases of potato including common scab, verticillium wilt, and various plant parasitic nematodes at five field locations for up 2 years. Swine manure (SwM) also controlled these diseases but at only one of several locations tested. Laboratory studies, using microcosms containing mixtures of soils, amendments, and microsclerotia (MS) of Verticillium dahliae, either buried in soil or suspended in the headspace, revealed that MS were killed within 7-10 days after incorporation of high N-amendments (0.5-2.0% w/w) due to accumulation of ammonia (NH3). A delayed MS kill, which occurred after 2-4 weeks, was caused by production of nitrous acid (HNO2). Factors that enhanced NH3 and HNO2 accumulation promoted MS kill. The levels of soil organic C and acid buffering capacity were shown to strongly influence accumulation of NH3 and HNO2 respectively. In bioassay tests HNO2 was at least 100 times more toxic than NH3. SwM also killed V. dahliae by generation of HNO2. In addition, SwM contains a volatile component(s) that kills V. dahliae within one day after application. The toxicity of the volatiles was evident in low pH soils but all activity was lost in neutral to basic soils. Soil moisture also diluted the active products. Although these amendments killed plant pathogens, soil microbial populations increased by 100-1000-fold after application, indicating that not all organisms were affected.