NM8003 - Development and evaluation of maximum liquid manure land application rates and the risk associated with post application rainfall

The ministry funded this project through the Nutrient Management Joint Research Program (2006-2007). The program supported the development of environmentally effective and scientifically robust management practice options for land application of agricultural and non-agricultural source materials in Ontario.

Lead researcher

Ron Fleming, University of Guelph Ridgetown Campus and Dr. Greg Wall, Soil Resource Group

Objectives

The project will develop maximum liquid manure application rates based on the SCS method for runoff estimation. The estimated application rates will be field tested for different hydrologic soil groups of the province and seasons of the year.

1. Develop and evaluate science-based maximum land application rates for liquid manure.
2. Assess the impact of post application rainfall events on runoff on different field slopes representative of hydrologic soil groups of Ontario.
3. Propose maximum land application rates on pre-tilled and untilled land surfaces for soils and slopes of Ontario for typical liquid manure types.
4. Make relevant recommendations to minimize the risk of surface water contamination.

Expected benefits

The study will provide recommended seasonal maximum liquid manure application rates and slope limitations for prescribed liquid materials in Ontario. Further recommendations will be made to minimize the risk of surface water impact associated with runoff from land following application of manure.

Results

If too much liquid manure is applied to farmland, there is a risk of runoff. Any nearby surface water could therefore become contaminated. In an effort to establish "how much is too much", a research project was carried out on farms in southwestern Ontario.

This two year study (2007, 2008) looked into the importance of soil type, land slope, manure dry matter content, pre-tillage, application rate and other factors in determining the risk of manure runoff. There were several elements to the study. One part evaluated the suitability of using a prediction model (SCS Method) initially developed for rainfall runoff. Field scale and plot scale studies were run to examine the conditions under which runoff occurred and the volumes of runoff that were possible. Finally, rainfall simulation was used to assess the threat of runoff when rain falls on a field that has recently received manure.

The study showed that the dry matter content of the manure had the greatest influence on the likelihood of runoff occurring. The liquid cattle manure (dry matter in the range 7.0 to 11.5%) had much less tendency to run off than the liquid swine manure (dry matter in the range 2.2 to 5.2). For the higher dry matter manures, the maximum application rate allowed for approval of a Nutrient Management Plan to prevent the over-application of nutrients such as nitrogen and phosphorus would almost certainly be lower than the rate needed to create runoff.

The slope of the land was important. For slopes of greater than 9%, there was a greater risk of runoff. Also, runoff volumes were much more variable (depending on dry matter content) than at lower slopes. The SCS method provided reasonable estimates of maximum rates before runoff occurred for some of the manures having lower dry matter content. However, because the SCS method did not take into account higher dry matter manure, its usefulness for this application is limited.

Finally, the maximum distance that runoff travelled was not measured in the study. However, it was in the range of a few metres from the across-slope application, and not tens of metres. For the field scale trials, runoff was defined as occurring when liquid moved more than one meter from the edge of the spread pattern, a distance that would potentially affect the amount of nutrients applied to a crop row. The small plot studies showed, at least on the medium to low slopes, that runoff volume dropped quickly as the distance from the spread area increased. Considerable movement of manure constituents at greater distances could happen in the event of a heavy rainfall shortly after manure spreading.

Parameters studied

• Manure application rate and type
• surface flow

Recommendations relevant to nutrient management

• manure dry matter was a significant contributor to the risk of runoff at the time of manure application. The potential runoff of manure increases significantly with the application of lower dry matter manure. The Nutrient Management Workbook does not take into account manure dry matter when assessing runoff risk
• for dairy manure having a dry matter content of around 8%, maximum application rates before runoff occurred were relatively high. Limitations imposed by nutrient loading limits to a field will be adequate to control application runoff for this manure type
• the SCS Method of determining curve numbers and maximum liquid loading rates based on site conditions was limited in its usefulness for all manure types because it did not consider liquid manure of higher dry matter content
• the risk of runoff from heavy rainfall after manure application was significant and the impact was similar between manure types
• there were differences in the risk of runoff between Hydrologic Soil Groups for the lower dry matter swine manure. HSG's C and D posed a greater runoff risk than HSG A. However, there were no significant differences between HSGs for the higher dry matter dairy manure
• the greater the field slope, the greater the risk of runoff occurring once manure application or subsequent rainfall exceeds the soil infiltration rate, especially for slopes above 9%
• increased tillage intensity across slope appeared more significant in reducing potential runoff than HSG on the sites with pre-tillage
• seasonal effects of typical and varying soil moisture conditions near the surface were not significant for liquid loading of manures applied all at once
• conditions that encouraged the potential for runoff by limiting infiltration (such as compacted soil or frozen ground near the surface) of lower dry matter liquid restricted rates more significantly than HSG. Current guidelines do not address these field areas that are susceptible to increased runoff
  

Related information

Other projects funded through the Nutrient Management Joint Research Program:

• in 2006
• in 2007