Nitrogen (N) is an essential plant element. However, its supply from soil compared to its demand by crops as well as pasture plants is the most limiting amongst soil nutrients. Pastures respond well to N application. N utilization efficiency can be 9-28 kg dry matter per 1 kg N applied. As a result, N fertilisers are increasingly applied for high pasture production. How pastures respond to N and the factors affecting responses are crucial to the efficient use of N fertilisers. After fertiliser N is applied, N is rapidly absorbed into plants and growth stimulated via improvement of root systems and photosynthetic activity. Pasture production increases depend on botanical composition, cultivars and physiological state. Pasture growth is improved immediately after N application. This effect can last into the next growing period following initial defoliation. The carryover N effect may increase plant growth, but can be negative in some cases. New Zealand studies showed positive N carryover effects present for first two cuts, inconsistent at third, and negative for fourth and fifth cuts. Pasture composition, N fixation by legumes and herbage nutrient concentration all respond to N application. Pastures response to N flux varies with various factors, including N form, rate applied, and frequency and timing of application. Dry matter yields in pure grass pastures increases linearly with N application rate up to 200-400 kg N ha-1 per year. Split N applications improve annual yield and seasonal yield distribution. Spring applications gave greater N responses than autumn applications. N responses are also affected by climate, geographical factors, and soil factors, such as type, texture, drainage, pH, fertility, moisture and temperature.

Farmers are increasingly using management systems such as moving cows out of paddocks onto stand-off pads to protect wet soils from damage during winter. Studies were carried out to investigate nutrient and faecal bacterial retention or loss from stand-off pad materials. A preliminary laboratory study found that a range of natural materials, including crushed pine bark, wood chips, zeolite and soil can retain between 66% and 76% of applied cows' excreta nitrogen (N). Zeolite was found to be particularly good at reducing ammonia (NH3) volatilisation losses from the columns. A field-scale standoff pad study at a Waikato dairy farm, in the winter season of 2005, indicated that carbon (C)-rich materials including both bark and sawdust can be used as standoff pad materials with effective retention of N and faecal bacteria. Both bark and sawdust pads retained about 60% of deposited excreta N. Substantially more Escherichia coli were recovered in the drainage from the bark pad (total yield 3.1 x 1011 E. coli) than from the sawdust pad (total yield 7.5 x 109 E. coli) demonstrating that sawdust was more effective than bark in retaining these faecal bacteria. Keywords: stand-off pads, winter management, dairy, nitrogen, faecal bacteria, natural materials