Does ‘Splitting' N Fertiliser Application Decrease N Leaching from Turfgrass?.
Louise Barton, George Wan, Renee Buck, and Timothy Colmer. The University of Western Australia, School of Plant Biology, 35 Stirling Hwy, Nedlands, Australia
Applying water-soluble N fertilisers ‘sparingly and frequently’ is a recommended approach for minimising N leaching from turfgrass; yet, optimal frequencies have not been reported. The effect of different N fertiliser regimes on N leaching from turfgrass (Pennisetum cladestinum) grown on a free-draining sandy soil in a Mediterranean-type climate was evaluated for 24 months. The field study included two turfgrass ages (plots established from 20 week or 20 year old ‘sod’), three N application rates (50, 100, or 150 kg N ha-1 yr-1) and three fertiliser application frequencies (twice a year, four times a year, or every four weeks).There were three replicate plots per treatment, plus turfgrass plots that received no N fertiliser. Irrigation occurred every second day by replacing 60% of net evaporation; a rate shown to maintain growth and not cause excessive drainage from the root-zone in the study environment. Nitrogen leaching was assessed by measuring the leachate volumes and concentrations of N species leached from soil lysimeters (250 mm in diameter by 950 mm in length) installed in 10 m2 turfgrass plots. Turfgrass growth (dry matter production) and quality (colour, surface hardness) of the plots were measured throughout the study. After 24 months, N leaching did not vary between turfgrass age, fertiliser rate or fertiliser application frequency. On average, 45 kg kg N ha-1 was leached from N fertilised treatments and 40 kg N ha-1 was leached from non-fertilised treatments. Approximately 50% of nitrogen leaching occurred in the first three months following planting. Turfgrass growth and quality was more consistent when annual N fertiliser was split across four applications. Reducing the frequency of application tended to increase the risk of ‘scalping’ in spring and autumn, especially at the highest N application rate. Nitrogen losses appear to be low from established turfgrass that is not over-irrigated and has received moderate (e.g., up 150 kg N ha-1 yr-1) amounts of N fertiliser.