Optimising nitrogen fertiliser use on turf

• To determine the optimum fertiliser nitrogen requirements for selected warm-season turfgrasses
• To consider how and when nitrogen should be applied to maximise turf quality and minimise mowing

Cynodon dactylon

• Wintergreen and FLoraTeX™

Digitaria didactyla

• Aussiblue^A

Paspalum vaginatum

• Sea Isle 1^A

Pennisetum clandestinum 

• Male-sterile kikuyu

Stenotaphrum secundatum

• Sir Walter^A

There were six fertiliser N treatments (0, 50, 100, 200, 300 & 400 kg N/ha/year) applied as equal split applications in early September, November, January, March, and May. As well as taking dry matter yields every 2 weeks during the warmer months (4-weekly during winter), ratings were made of turf quality, density, colour, and weed content in each 2 x 2 m fertiliser plot.

• A nitrogen shortfall is commonly experienced in spring, suggesting that rather than applying fertiliser N regularly in equal amounts during the growing season, it may be best to weight application towards the beginning of the growing season, with one or two larger initial dressings during spring followed by smaller amounts during the hotter, wetter summer months.
• During the summer months, the grasses tend to run out of N within the two months leading up to the next split application, particularly if heavy rains have fallen.
• The grasses responded differently to applications of nitrogen. This impacted on the composition of the grass sward. For example: high and medium fertility grasses dominated mixed swards where there was high available soil nitrogen and low fertility grasses dominated mixed swards with low available soil nitrogen.
• Kikuyu has the highest fertility demand, needing around 300-400 kg N/ha/year for optimal growth and high quality use.
• Optimal growth in the green couches studied was achieved at around 300 kg N/ha/year.
• High nitrogen applications may increase the susceptibility of FLoraTeX™ to patch disease during early spring
• Sir Walter^A and Sea Isle 1^A are medium fertility grasses, with optimum requirements of around 200 kg N/ha/year. Higher levels of nitrogen should be avoided, particularly during the hot summer-early autumn months, as the rapid growth this encourages also increases mowing requirements.
• Sir Walter^A maintains good density at lower N rates, but often lacks acceptable colour at those levels.
• Aussiblue^A was the least nitrogen demanding, with optimum requirements of around 100-200 kg N/ha/year. Aussiblue^A resisted invasion by other grasses, even when no nitrogen was applied, but still responded to the highest rate of applied nitrogen (400 kg N/ha/year).