Eric Miltner, Gwen Stahnke, Paul Backman, and Bob Ingram

Introduction

Calcareous Sands in Putting Greens

Poor performance or failure of putting greens constructed with calcareous sands has been reported through golf superintendents and USGA agronomists. The USGA recommends against using these materials, but in many areas of the country economic considerations necessitate their use. In addition, there is no reported scientific evidence of their fitness for use or mechanisms for potential unsuitability. This USGA funded project will examine the potential for weathering of sands of varying CaCO3 (calcium carbonate, or calcite) content. It is our hypothesis that calcite may dissolve under acidic conditions, caused by fertilizer application, and reprecipitate when pH rises due to off season non-fertilization periods. Calcite precipitation may disrupt soil physical properties, and changes in particle size distribution could occur if calcite acts as a cementing agent. Sand samples are being collected nationwide and evaluated for calcite content. Weathering potential as affected by sand source and fertility practices will be evaluated in column studies. Calcareous sand putting greens of varying ages are being sampled and analyzed for changes in physical and chemical properties.

Seasonal Nitrogen Dynamics

Nitrogenous fertilizers are applied to turfgrass throughout the growing season and even in non-growth periods. In the Pacific Northwest in particular, there is not a single month during the year where fertilization would be ruled out. Although most managers have developed an understanding of the visual responses to fertilization at different times, there is little information concerning actual plant utilization. In addition, nitrogen application often stimulates release of organic soil N through the activity of soil microorganisms. In this experiment, we are investigating recovery of N in leaf tissue following fertilizer application during different months of the year. Although this information is not a substitute for visual plant response, it may be another tool that can be used to optimize N use efficiency. This is important in both turf health and environmental quality.

Cultivation and Soil Organic Nitrogen

Turfgrass communities generally develop relatively high soil organic matter contents, especially in the top few inches of soil. This is true even if the thatch layer is excluded from consideration. Contained in this organic matter, among other things, is a large pool of nitrogen (perhaps 40 to 60 lb N per 1000 ft² in the top 6 inches of a mature turf community). This happens in part due to high turnover rates of roots and other plant parts. Areas converted to turf from other uses steadily build soil organic matter for periods of 5 to 15 years. Although this N is released naturally over time through the activity of soil microorganisms, the rate is very slow, and immobilization (organic N accumulation) generally outpaces mineralization (organic matter breakdown) in regularly fertilized communities. Organic matter has many positive physical and chemical benefits, but turf stands may develop more organic matter than is needed. Soil cultivation helps to break down organic matter, releasing N and other plant nutrients. We are investigating the effects of various cultivation techniques, including solid and hollow tine cultivation, water injection cultivation, and vertical mowing, on nitrogen availability and soil organic matter content. In addition to providing physical benefits, cultivation may be a tool that helps to release some of the N that has accumulated in soil organic pools, thereby improving N use efficiency.