Development and Evaluation of Subsurface Application Technology for Solid Organic Fertilizers

Abstract

The only readily available land application method for solid organic fertilizers (e.g. manure, compost) is surface broadcast application. However, the practice of injecting liquid manure directly under the soil surface is widely used and has demonstrated benefits in terms of reduced odor and ammonia emissions as well as decreased losses of nutrients by runoff or evaporation. The objective of the work reported herein was to develop an implement to apply solid organic fertilizers directly under the soil surface. The design criteria for the injection system included a maximum application rate of 19.8 Mg/ha at a travel speed of 4.8 km/h and a 406-mm injector spacing. The final configuration of the injection system features a feeding screw conveyor (168-mm diameter and 171-mm pitch) that is tapered to join a flexible screw conveyor 89 mm in diameter. The flexible screw conveyor runs in a flexible plastic hose (102-mm inside diameter) that brings the product to a coulter opener. The system was capable of outputting 1.9 kg/s of beef cattle manure with straw bedding compared to a target rate of 1.1 kg/s. The hydraulic power requirements were found to be 5.1 kW-s/kg per injection unit. A three-year agronomic evaluation of the technology was performed. The results indicated that there was evidence of slightly increased recovery of nitrogen and phosphorus in the manure when it was placed in the soil. In the last year of the study, there appear to be some additional benefit of the injection on crop yield. This may be explained by the injection enhancing the decomposition of the manure to plant-available inorganic forms of nutrients that plant roots can access better. Complementary results suggest that the injection of solid manure is an effective way of reducing odors from land application. However, the overall results obtained for beef cattle manure at the test site indicated that the agronomic benefits of in-soil placement of the solid manure were relatively limited and may not justify the additional associated costs.