A Novel Organic Soil Amendment with Consistent Composition Promotes Soil Microbial Respiration and Growth of Horticultural Plants.

Urban gardening and landscape maintenance practitioners use a variety of products such as fertilizers, composts, and wood mulch to support plant growth. The variability of carbon content inherent in municipal and commercial composts and other soil amendments tend to create soil and plant responses that are inconsistent. Our previous research with composts indicate that growth promoting products should have a C:N ratio of approximately 20:1. We are now evaluating the effect of Precision Organics Test Product (POTP), which is produced from agricultural by-products. Formulated as a soil amendment, POTP is consistently produced with precise carbon components, particle size, moisture content and C:N ratio. We conducted comparison studies of POTP (C:N=20:1), a municipal compost (C:N<20:1) and a traditional fertilizer (C:N<1:1) on microbial activity in clay subsoil (OM% 0.9, pH 8.4) and growth of Early Scarlet Globe radish plants. Our data shows that POTP promotes significantly higher microbial respiration rates than are present in soil alone, soil plus fertilizer, or soil plus compost. POTP also promoted significantly larger above and below ground growth of radishes over clay subsoil alone, or clay subsoil supplemented with compost or fertilizer. Additional studies are examining the impact of POTP, compost and fertilizers, alone and in combination, on microbial respiration and plant growth in top soils (OM% 1.5, pH 7.6) for tomatoes, river birch seedlings and turf grasses. Results of these studies will be included.