Guideline Index

Chapter 10 - Keeping Nutrients on Farm

10.1 Introduction

In this section:

10.1.1 Importance

Keeping nutrients on dairy farms is important for several reasons including:

Nutrients drive dairy production, so excess nutrients lost from a farm are literally ‘money down the drain’ and a lost opportunity for higher yields. Compounding the loss, the nutrients may then have a negative impact on the off-farm environment. Keeping nutrients on the farm makes financial and environmental sense.

‘Only a quarter of the nutrients brought onto a dairy farm leave it in product’

Considering the bigger picture of nutrient use in agriculture, there are questions about the sustainability of current nutrient applications and management. Will farmers in the future have the same access to nutrients as those of today? Keeping nutrients on farm will help ensure they do.

Along with the question of sustainable use, the possibility of adverse environmental impacts also attracts the interest of community groups. Hence, both have the potential to result in regulations on fertiliser use and / or consumer action to demand improved management.

Studies of dairy farms across Australia in the ‘Accounting for Nutrients’ project, have shown that;

  • There is large variation in the nutrient status of soils on dairy farms, between farms and within and between paddocks on individual farms.
  • On average, there are excess nutrients available, implying low efficiency in converting nutrients to milk and potentially, subsequent losses to the environment – which confirms the results of other research.
  • There is a wide variation in nutrient efficiencies between farms, indicating that improvements are feasible in many situations.

For more information on Accounting for Nutrients, see: Cost of production

Some paddocks on dairy farms may be under-fertilised, but many are not. The Accounting for Nutrients project revealed that of the 37 conventional dairy farms studied around Australia:

  • 20% of pasture paddocks had more than three times the required level of phosphorus (Olsen P of 20 mg/kg). Phosphorus levels in paddocks close to the dairy were often two to three times those 2km from the dairy and four times higher than those 4km away.
  • All dairy farms are likely to have surplus nitrogen due to conversion inefficiencies, high concentrations in urine, and poor storage in soils. Nitrogen is lost with water run-off, leaching, or to the atmosphere. Nitrogen surpluses rise in proportion to milk production.
  • The average soil test levels for sulphur were twice the recommended level for pasture (KCl-40 of 10 mg/kg).
  • The average soil test levels for potassium were twice the recommended level for pasture (Colwell K of 140 mg/kg) and three times the level in 20% of cases.

Phosphorus and sulphur levels were substantially lower on organically farmed properties, but not below levels required for productive pastures. If no further phosphorus or sulphur was applied to the high level conventional paddocks for several years, it is unlikely that pasture productivity would suffer. Soil potassium levels were similar between conventional and organic dairy farms (Department of Primary Industries Victoria (n.d.)a).

There are clear opportunities for many dairy farmers to reduce fertiliser applications to high nutrient level paddocks; thereby reducing costs without compromising production, and hence resulting in higher net profit. The value of lost nutrient inputs will increase as do fertiliser costs.

For some case studies, highlighting the savings to be made, see:

Detrimental influences on the cost of production can also come about due to animal health and productivity impacts due to excessive nutrient intake. High potassium levels can contribute to metabolic disorders such as grass tetany and milk fever, while high nitrate content in pastures can trigger nitrate poisoning (see Chapter 12.6.1 for more information). Excessive calcium and magnesium have also been associated with poor stock health. Environmental impacts

Many excess nutrients are removed in water – either in surface flows or groundwater.

In surface waters, nutrients can stimulate the growth of algae, some of which can be poisonous like types of nitrogen-fixing ‘blue-green algae’. Surges in the growth of aquatic plants and algae can also leave an unwanted legacy. As they die, they are decomposed by microorganisms such as bacteria, which use up the available oxygen in the water – and lead to fish deaths as a consequence (Carpenter et al, 1998). The availability of excess nutrients can also change the ecology of a water body, leading to the replacement of aquatic plants or macro-algae by micro-algae (Harris, 2002).

In groundwater, high concentrations of nutrients, particularly nitrogen, can lead to human health risks. Excess levels of nitrate have been associated with ‘blue baby syndrome’, although the relationship is not clear. When introduced to waterways, pathogens from dairy cows can also pose a public health risk and, in some situations, a risk to young stock. As pathogens often follow similar pathways to those of excess nutrients, some practices that reduce nutrient losses will also help reduce the risk of water contamination by dairy pathogens. Nitrogen leaching may also increase the acidity of soil, necessitating treatment with lime.

Minimise trade-offs

Agronomic optimal nutrient concentrations are often greater than safe environmental limits but, as the following graph indicates, it is possible to obtain optimal production without challenging aspects of the environment. In this case, soil phosphorus levels for optimal pasture production are below the level at which there is a significant increase in the risk of phosphorus being lost in sub-surface drainage. The key message is to consider the impact of nutrient levels on the environment as well as on production and to avoid exceeding agronomic requirements to minimise impacts on the environment.

Figure 10.1   Agricultural optimum (up arrow) versus environmental impact (down arrow) for P loss in subsurface drainage (as estimated by 0.01M CaCl2-P).  Data are from plots receiving different rates of superphosphate (SSP; kg ha-1 yr-1) at Canterbury, NZ (McDowell, 2012).
Figure 10.1 Agricultural optimum (up arrow) versus environmental impact (down arrow) for P loss in subsurface drainage (as estimated by 0.01M CaCl2-P). Data are from plots receiving different rates of superphosphate (SSP; kg ha-1 yr-1) at Canterbury, NZ (McDowell, 2012).

Not all areas are of equal risk of losing nutrients to the environment. Some sites, referred to as ‘Critical Source Areas’ or ‘Hot Spots’, are more liable to pose a risk. These areas are typically wet and have high nutrient levels. Identifying and managing critical source areas are important ways to keep nutrients on farms. See Section 10.3.3 for more information.

Gaseous losses (e.g. nitrous oxide from soils, methane from cows and effluent and ammonia from ammonium-based fertilisers) are increasingly important in a carbon economy that is designed to reduce greenhouse gas emissions. Sustainable use

Nutrients are a critical factor driving dairy production. Global populations and their requirements for food are increasing yet, in some cases, questions are being raised about how much access producers will have to nutrients in the future. In that scenario, nutrients will be increasingly important and valuable.

As a generalisation, Australian soils tend to be very old and low in nutrients, making nutrient inputs an important contributor to high levels of productivity. Modern farming systems tend to import nutrients, such as feeds and fertilisers, to boost production, with relatively little recycling. Many nutrients are shipped out in produce, ultimately entering urban waste treatment systems and then oceans, or lost to the off-farm environment (Cribb, 2006; and Gourley & Weaver, 2012). Community responses

Communities around the world, through organisations and consumer reactions, have pressured governments and food producers in response to environmental and sustainability issues, as outlined previously. The responses range from local to multi-national in scale and include:

  • Regulations on nutrient applications – e.g. capping fertiliser application rates or stocking rates, limiting the types of fertiliser to be applied, or requiring nutrient management plans or budgets and capping the ‘loss’ component.
  • Public campaigns – e.g. detracting from the credentials and image of the dairy industry to invite regulations, consumer backlash, or additional barriers to trade.

Some regulations are now evident in Australia, with controls on fertiliser use being introduced to protect the Great Barrier Reef (Qld) and Peel Harvey Inlet (WA). For more information, see Gourley & Weaver (2012). There are also ‘softer’ options occurring, involving combinations of research, extension, incentives and regulation, affecting both fertiliser and milk supply-chains. Wise use of nutrients, and demonstration of that management, will be required to reduce the risk of increased regulation of farming activities.

10.1.2 Management principles

Research has shown there are areas on dairy farms with an oversupply of nutrients. There are opportunities for dairy farmers to improve the efficiency at which nutrients are converted to produce, to redistribute nutrients on-farm and to curtail off-farm losses.

The key management principles for dairy farmers to follow are to:

  • Understand nutrients – know about nutrient cycles; where nutrients come from, the transformations they undergo and the pathways they follow.
  • Plan to retain nutrients on-farm – apply the understanding of nutrients to plan for optimal productive efficiency and to contain losses; and check to see the plan is followed and succeeding.
  • Optimise production – get as much production from applied nutrients as possible by focusing on the ‘4Rs’ (the right sources of nutrients, in the right place, at the right rate and right time), and recycle and redistribute nutrients within that framework; especially in the more resilient areas of a farm.
  • Minimise losses – take special care to avoid direct losses and to lock-up or re-use excess nutrients; especially in areas more prone to environmental loss (critical source areas).

These principles, along with the key strategies to address them, are discussed in the following sections.