Evaluation of nitrogen source, phosphorus rate and mixing depth for growth and establishment of Poa pratensis L. on sand-based systems
Nitrogen is a component of the proteins, enzymes, amino acids, and many other biochemicals in plants required to maintain color and density of grasses and for the restoration of healthy conditions following environmental stress. Phosphorus is an important element ofthe phospholipids that help form the plant cell membranes. The suitable formation of these membranes is dependent on a readily available source ofP to the plant. Mobility and availability of nutrients varies with several factors such as application frequency, placement in the soil, and the amount of irrigation or precipitation, especially in sand-based systems. Frequent applications ofN are used to reduce N loss by leaching because N may be easily leached from a sand-based system. Use of slow-release N sources has been promoted as a more efficient N fertilizer strategy. Phosphorus mobility and availability varies with several factors such as application frequency, placement in the soil, and the amount of irrigation or precipitation. The objectives of this study were to compare urea and methylene urea rate at 146 and 293 kg N•ha-1 at four mixing depths (0, 7.6, 15.2, and 22.9 em) in a sand-based system (Chapter. 2) and to evaluate Prate at 146 and 293 kg P•ha-1 at four mixing depths (0, 7.6, 15.2, and 22.9 em) in a sand-based system (Chapter. 3). Grass clipping samples were collected every two weeks, dried, and weighed. Root dry weight and root organic matter weight also were evaluated at the end of the study. Leachate was collected weekly and analyzed for nitrate-nitrogen (N03-N) and P concentrations. Split applications of urea on the surface produced the largest clipping yield and the best NUE for total mass yield, with the lowest N03-N loss due to leaching. Methylene urea at the 22.9 em mixing depth resulted in more grass growth, smaller N03-N losses, and better NUE for total mass than urea placed below the surface. Grass treated with 293 kg P·ha-1 produced 2-30% more Pin the tissue than treatments of 146 kg P·ha-1 , with the exception of the application at the 15.2 em mixing depth. No difference was found between applications made to the surface and those at the 7.6 em mixing depth. Surface application with 146 and 293 kg P·ha- 1 produced 8-10% and 16-20% more P in tissue than subsurface applications, respectively.