Report: TR 2011/38
Author: DJ Houlbrooke and RM Monaghan (AgResearch), M McLeod (Landcare Research)
The safe application of farm dairy effluent (FDE) to land has proven to be a challenge for dairy farmers and regulatory authorities throughout New Zealand. Recent research has identified that poorly performing FDE systems can have harmful effects on water quality, particularly when direct losses of FDE with high concentrations of contaminants (phosphorus, nitrogen and faecal microbes) discharge, drain or runoff directly to surface water bodies.
Land application of FDE has proven particularlyl difficult when it has occurred on soils with a high degree of preferential flow, soils with artificial drainage or coarse structure, soils with infiltration or drainage impediments, or when applied to soils on rolling or hill country.
The effect of these conditions can be exacerbated by climate, where high rainfall can further contribute to the poor environmental performance of such land application systems. In comparison, well drained soils with fine to medium soil structure tend to exhibit matrix rather than preferential drainage flow, even under soil moisture conditions close to or at field capacity. These soils are therefore likely to pose a lower risk of direct loss of effluent contaminants. However, there is only limited research conducted in New Zealand on these lower risk soil types to test the hypothesis that FDE applications when soil water content (SWC) is at field capacity will not result in direct drainage losses. The issue of hydrophobicity and its potential impact on rapid re-wetting of dry, well-drained soils in rolling volcanic landscapes is still somewhat unknown.
AgResearch Ltd was engaged to provide management advice to regional councils regarding the effectiveness of effluent best management practices (BMPs) and the importance of soil and landscape risk features when applying FDE to land. During this process a risk framework/decision tool was developed to guide recommendations regarding minimum management practice and concept storage requirements, considering a soil’s inherent risk for direct losses of FDE contaminants during land application.
The risk framework was peer reviewed by soil scientists from AgResearch, Landcare Research, Massey University, Lincoln University and Plant and Food Research. Furthermore, the development of an industry code of practice for effluent designers and installers is nearing completion and due for final release in mid 2010. The code uses an adapted version of the FDE risk framework as a design standard in order to recommend concept storage requirements for installers to design against.
This report aims to illustrate how soil drainage mechanisms influence the likelihood of direct drainage losses of applied FDE. It presents a FDE risk framework that can be used as a guide to identify minimum concept storage requirements land application practices for a range of soil and landscape categories.
|2||Water and solute transport mechanisms in soil||7|
|3||Best management practices for land application of farm dairy effluent||12|
|3.2||Low application rate tools||13|
|4.1||Soils that exhibit overland flow||14|
|4.2||Soils that exhibit preferential flow||15|
|4.2.1||Categorisation of preferential flow risk||16|
|4.2.2||Soils in the Waikato region that exhibit preferential flow||18|
|4.2.3||Research studies of preferential flow losses||18|
|4.3||Soils that exhibit matrix flow||21|
|5||Recommendations to Environment Waikato||26|
|5.1||Minimum criteria for effluent management systems to achieve||26|
|5.1.1||Artificial drainage or coarse soil structure||27|
|5.1.2||Impeded drainage or low infiltration rate||27|
|5.1.3||Sloping land (>7°)||28|
|5.1.4||Well drained land||29|
|5.1.5||Other well drained but very stony flat land (>7°)||29|
|5.2||Further management considerations||30|
|5.3||Determining effluent land management units||31|
|5.4||Determining farm-specific effluent storage requirements||34|
|5.5||Improving on-farm management practice||36|