Guideline Index

Chapter 10: Keeping Nutrients on Farm

10.5 Minimise losses

The keys to minimising nutrient losses are:

10.5.1 Avoid direct loss from fertilisers, effluent and livestock

Direct losses are losses of nutrients from the farm system through a pathway with direct off-farm connectivity, e.g. by spreading fertiliser over flowing surface water. These can be almost immediate and come from inadequately managed:

10.5.1.1 Avoid direct loss from fertilisers

Some potential fertiliser losses are easy to avoid:

  • No applications direct to surface waters such as drains, creeks and dams – maintaining a buffer between fertilised pastures and surface waters or drains.
  • >No applications to ‘hot spots’ – avoiding critical source areas with strong connectivity; such as pugged paddocks adjacent streams or bare soils, laneways and yards.
  • Minimise irrigation run-off – ensuring there is no run-off after applying fertilisers, or not applying fertilisers to a buffer strip at the end of irrigation bays.
  • Others require some planning:
  • No applications of nitrogen within 5 days of an anticipated run-off event.
  • Minimise ammonia volatilisation from urea applied during the warmer months by irrigating fertiliser into the soil, but avoid run-off. Where irrigation is not possible, losses can be reduced significantly by applying urea 2-3 days before grazing (Warning: lumps of urea ingested by animals can cause ammonia toxicity). See Chapter 12.3 for further information regarding minimising nitrogen losses.
  • No applications of phosphorus within 7 days of an anticipated run-off event or when soils are freely draining after heavy rains.

To reduce nutrient losses from fertilisers it is necessary to consider the ‘4Rs’ framework of:

Right source

Stable, slow release, forms of fertiliser pose least risk to the environment, but may not be cost effective or necessary in many situations. Using fertilisers of low solubility can reduce losses by 0-20% depending on the circumstances (McDowell & Nash, 2012). See Chapter 11 and Chapter 12 for information on how to select the right source of fertiliser for different situations and conditions.

Right place

Special attention is needed for critical source areas and to avoid direct applications to water-ways. Following the Fertcare program guidelines for application will address those concerns. Select areas with low nutrient levels for added applications. In cultivation paddocks, ensure pre-plant fertilisers are incorporated and covered by loose soil.

Right rate

A common goal is to meet the needs of plants by ensuring nutrients, particularly N, K and S, are available at rates to match plant uptake. Nutrient types and rates should be targeted for different areas of the farm based on soil test results, critical levels for plant growth and nutrient budgets. Some ‘rules of thumb’ are summarised below and can be seen in full at:

http://www.nitrogen.unimelb.edu.au/ :

  • Apply N at 30-50 kg/ha per application to meet plant growth requirements, at intervals of at least 21 – 28 days respectively during periods of active plant growth.
  • Where annual N applications exceed 250 kg N/ha/yr, soil testing and applying lime may be required if fertilising at higher rates in high production paddocks.
  • Don’t apply P if soil test levels are above those where a pasture response is likely. The critical level will vary with the phosphorus buffering capacity (PBI) of the soil and the desired level of production from the paddock – Refer Error! Reference source not found..

Ensuring spreading equipment is Accu-spread accredited will result in an even distribution of fertilisers within the targeted application zone.

Right time

Timing applications to meet plant needs is a priority, for example as needed for Nitrogen. However, consideration must also be given to optimising uptake and minimising losses. Timing activities (e.g. not applying fertilisers when heavy rainfall and run-off is imminent) is a management option to reduce nutrient losses. Seven-day forecasts from the Bureau of Meteorology can be useful guides to help determine the risk of significant run-off occurring. Losses that may be controlled by management are sometimes termed ‘incidental losses’. Avoiding run-off from irrigation is another example.

Applying nitrogen on a cool, dry surface, a day prior to adequate ‘watering in’ rain but not before heavy, run-off inducing rainfall is one way to optimise production and minimise losses through volatilisation and run-off.

10.5.1.2 Avoid direct loss from effluent

Effluent from milking sheds, feedpads and yards should be effectively captured and stored for treatment. Designing, and maintaining, correctly sized pre-treatment systems, ponds and sumps to cope with peak loads (e.g. capturing a ‘first flush’ in storms but diverting cleaner subsequent water) is the first step. Similarly, laneways (especially those subject to heavy traffic and/or draining direct to a water-body) should be constructed and maintained with adequate shape and crown to disperse nutrient-rich run-off in a low-risk manner. Constructing drainage diversion humps or ‘whoa boys’ that direct sloping laneway run-off to grassed areas is one way to achieve this.

The rule of thumb that recycled water should be applied as thinly as possible over as large an area as possible is as relevant to recycled dairy effluent as it is to other recycled wastewaters, although opportunities on dairy farms may be limited and require additional irrigation infrastructure. It is particularly important to avoid applying recycled effluent to saturated soils where run-off will occur. Having adequate storage capacity and irrigation capacity are fundamental for that. A soil-water budget can help in planning an appropriate system. If losses remain a risk, then additional treatment may be an option to reduce nutrient loads (e.g. high rate algal ponds, where nutrients from effluent help grow algae which are harvested for use as fertiliser or stock-feed, have been trialled to reduce phosphorus levels) (McDowell et al, 2004).

Effluent irrigation systems may be prone to blockages, which can in turn lead to stoppages or overflows, which result in run-off. Having fail-safe tools like breakdown alerts and automatic shut-downs can help manage that risk (Hanly, 2012).

Refer to Chapter 13 for further information about using dairy effluent.

10.5.1.3 Avoid direct loss from stock

Keeping stock out of watercourses is a fundamental approach to keep nutrients and pathogens out of waterways. Fencing, creek crossings and alternative watering points are prerequisites. ‘Hot spots’ like troughs and gates should also be carefully sited.

Pugged areas with strong connectivity to water are a potential ‘critical source area’ and should not be grazed, to avoid direct losses. For more information on assessing pugging and planning recovery, see GippsDairy (2011). Changed grazing management (e.g. on-off grazing) or feedpads may be necessary.

10.5.2 Reduce and reuse run-off

Water movement is a key driver of risk, so reducing run-off and deep-drainage will help reduce the loss of nutrients from dairy farms. Irrigation should be managed to minimise overwatering and waterlogging and should consider the water holding capacity of the soil type. Irrigation systems that result in good distribution uniformity (low pressure systems) and scheduling based on plant water usage and accurate soil moisture monitoring equipment can assist in this regard.

It is necessary, however, to consider individual farms and sub-catchments in their own right, as general rules do not always apply. For example, while boggy areas on farms may have been drained to increase production, there can be merit from a nutrient management perspective in some locations in slowing the flow of water and reducing run-off. Taking a whole-farm, or even sub-catchment, view can help to identify opportunities to retain water and nutrients in a useful manner (e.g. to maximise water use efficiency as measured by pasture production / mm of rainfall) and to slow the rate of flow in local streams and hence reduce stream-bank erosion.

This may be as simple as retaining thick grass buffers adjacent to water lines, especially small streams in paddocks. At the other extreme, it could be constructing an artificial wetland to take water from low-lying areas or for water drained from boggy areas. Care should be taken with natural wetlands, but there may be opportunities to reduce stock access or reinstate wetland vegetation and increase their capacity as a nutrient sink, without harming their ecology.

An option for flood irrigation is to not fertilise the end of bays, providing a buffer as recommended for waterways, and to avoid run-off. Re-use dams may also be installed, increasing the efficiency of water use and recycling nutrients.

Avoiding water movement that results in erosion will also reduce the loss of nutrients from farms. Permanent pastures and adopting conservation tillage during pasture renovation or the growing of fodder crops will help maintain groundcover (e.g. retaining residues or sowing cover crops), surface roughness and infiltration. Careful periodic deep cultivation can also be beneficial, incorporating nutrient rich top-soil within the deeper soil profile and closing off macro-pores through which P may be lost (McDowell et al, 2004). Diversion or contour banks can also slow water movement on sloping grounds.

Rehabilitating any eroding areas (including streambanks in some situations) and ensuring there is good ground-cover will retain soil and reduce the loss of nutrients. As with buffering waterways, it can be relatively easy and very beneficial to work on small order streams within paddocks.

10.5.3 Lock-up excess nutrients

Applying soil ameliorants to ‘lock-up’ nutrients may be an option for some situations; especially when focused on critical source areas – and when it makes the saved nutrients available for plant uptake.

For example, in Western Australia, bauxite has been applied when available as an economically feasible way to retain phosphorus in sandy, at-risk soils. Research is also showing that nitrification inhibitors can work in the field; although practical, well-tested applications have not been available for conventional Australian dairy farms (Eckard et al, 2008) but work is ongoing in this area. The N-inhibitors work by reducing the rate at which ammonium from the main sources, fertilisers and urine, is converted to nitrate and nitrous oxide. The process gives plants more time to take up both ammonium and nitrate ions, meaning more fertiliser is available to, and is used by, pastures; increasing productivity and reducing environmental losses (Cameron et al).