Improving manure through feed quality
Cycling nutrients of animals, soils and plants by effectively managing manure.
April 19, 2020 by Donna Fleury
Effectively managing and cycling nutrients – in animals through feed rations, in soils through manure applications and back through crops – is a fine balance. Nutrient management planning, feed ration analysis, manure testing and soil testing are all important components of balancing nutrients throughout the feeding and cropping system, and optimizing performance of animals and crops.
“Along with the ability to supply important nutrients, manure contributes to a positive effect on plant growth by enhancement of soil organic matter, contributing to important soil physical attributes such as water infiltration and storage, soil structure and others,” explains Jeff Schoenau, professor of soil science at the University of Saskatchewan. “Manure typically doesn’t have the nutrient balance that crops always need, so both manure testing and soil testing are important to determine the necessary adjustments, such as supplementation with commercial fertilizer. In some cases, unbalanced manure fertilizer application can lead to high soil test phosphorus (P) and potassium (K) levels beyond what crops can utilize, and possible supplementation with commercial fertilizers may be required to balance crop requirements.”
Livestock producers can also adjust animal diets to optimize animal performance, manage feeding costs and potentially reduce the amount of nutrient output that needs to be managed for crop production. “The concept of what goes into the animal as it affects what comes out in terms of nutrients is important,” Schoenau says. “Feed testing to understand the nutrient content for each feed ingredient and bioavailability can help balance and optimize the animal diet, and also assist in managing nutrient output in the manure.
“Any time there is a change in the feeding ration, analysis of the manure is a good idea to see how it may have affected the composition. The manure analysis determines the total nutrient content and helps predict the availability of those nutrients in order to make the best prescription for its use as a fertilizer when applied out in the field.”
With nutrient management, all sources – including manure – must be applied using the 4R principles – the right source at the right time, right place and right rate. Applying the 4R principles to manure is an effective way of getting maximum economic and agronomic benefit to plants while minimizing the risk of losses. Schoenau notes one important finding from their long-term research trials is when manure is managed the right way, nutrient loading and runoff issues do not appear to be a concern. Losses are minimized when manure is applied at “agronomically right rates,” or the rates at which the nutrient applied is balanced or matched by the amount of nutrient that leaves the system in crop harvest over the years. Precisely managing manure and fine-tuning rates can improve those responses and economic returns.
One challenge of utilizing manure is the dilute nature, with low concentration of nutrients per unit weight or volume compared to conventional fertilizer, and the amount required to apply at an agronomic rate. Applications of a few thousand gallons per acre of liquid effluent or a few tons per acre of solid manure are typically required in order to supply nutrients at an agronomic rate.
Schoenau adds, “Liquid manure sources tend to have a higher proportion of nutrients in available forms that plants can immediately use and are more valuable in providing available nutrients in the short term. Solid manure tends to have a lesser proportion of nutrients in inorganic forms that plants can immediately use, and the organic forms that dominate have to be converted or mineralized into inorganic plant available ions.
“The slow release of available N from decomposition of organic matter in manure typically provides available nutrients slowly over several years,” he says. “There are other important balance relationships – such as the carbon-to-nitrogen ratio in solid manures, the available nitrogen-to-sulphur ratios in liquid manures, and the nitrogen-to-phosphorus ratio in all manures – that we need to pay attention to so we get the best benefit out of those manure nutrients.”
One of the tools available to livestock producers is NMAN, a database of various animal manure samples, part of the larger AgriSuite – tools and calculators developed by the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA). “This database, which now probably numbers over 15,000 samples, is continually updated, including the nutrient values of N, P, K and micronutrients,” explains Christine Brown, Field Crops Sustainability Specialist with OMAFRA. “When doing a manure analysis, it is useful to compare your farm’s nutrient analysis with the database averages to see how they compare.”
Differences can be an indication that the ration needs to be tweaked. If some of the nutrients are higher than normal, it would be a good idea to talk to a nutritionist to understand why. It can also be a way to manage the nutrient levels in the manure, such as the use of phytase in pig and poultry rations for managing P, both for improving feeding efficiency and reducing nutrients in manure.
Brown emphasizes that without a manure analysis, understanding the value of the manure resource is difficult, as is determining application rates, timing and potential environmental outcomes.
“Along with manipulating nutrients in the feed ration, the manure analysis helps with manipulating nutrients at the pit or manure management stage and in the field application,” she says. “For some manure types, the nutrients can settle out in the pit, which provides an opportunity to manage nutrients differently. For example, pig manure can settle out in the pit leaving the top layer (first two or three feet) with high ammonium N but very low P levels.
“It is important to know where the nutrient layers change and make sure to test the manure. One strategy is to skim off this low P/high N layer and use it on corn fields that require high N inputs, but no additional P. The remainder of the manure that is higher in concentrated nutrients can be applied to fields further from the storage after harvest. This seems to work for liquid pig manure, but not liquid dairy manure.”
Brown adds good samples can help to fine-tune the application. “Mixing those samples together will give you a good idea of the average nutrient levels going into those fields, and help to fine-tune the additional commercial fertilizer that may be required usually for N but not for P or K, depending on the crop,” Brown says.
“The available N from the analysis is based on corn crop requirements, so other crops, such as wheat [which needs the nitrogen earlier in the season, when cool soils may delay availability], may result in a different application recommendation. We are encouraging producers to get a full analysis that includes organic matter, C:N ratios and a full nutrients package to not only help with better manure nutrient distribution to fields, but also to assist with manure being traded or sold for nutrient sources to other growers.”
There are some other factors to consider when recycling manure nutrients back into forage feed that is going to be fed again to livestock. “Manure in general tends to be quite high in available K content, so producers need to be aware that lands that have received repeated manure applications may have an excess of K relative to calcium (Ca) and magnesium (Mg) in the soil. This can ultimately produce a high ratio of K to Ca and Mg in the subsequent forage crop that could cause issues with tetany or milk fever in the cows,” Schoenau says.
“In a past research trial using low disturbance injection of liquid manure into forages – in one particularly cold, dry spring where forage growth was restricted – we had issues where grass at one of the sites had a fairly high nitrate content. In another in-field winter feeding trial with bales of differing N contents and C:N ratios – where the bales were fed, the forage growth the following year was positively influenced both by the nutrients in manure deposited in the field and also the nutrients from the leftover feed. These issues emphasize the importance of feed testing along with manure and soil testing as part of the nutrient utilization toolbox.”
Schoenau is currently involved in a research project at the University of Saskatchewan Livestock and Forage Centre of Excellence, looking at performance of variable rate precision application of solid cattle manure for barley silage production. “The preliminary results indicate the VR application worked well and was able to even out the productivity across the land area, identifying those low-lying areas in watershed basins where manure application rates could be reduced or eliminated without yield penalty,” he says.
“We need to strive to effectively recycle those nutrients in a system. A good example is where the animals are consuming feed from a land area and producing manure – and its associated nutrients from the feed – that is recycled back into the soil to grow more feed.”
For both livestock and crop producers looking to fully understand and optimize feed and nutrient management, the AgriSuite planning tools are a great place to start. The tools are useful for managing different types of feed rations, manure and crop nutrients, and alternative nutrient sources like anaerobic digestate. Visit Ontario.ca/agrisuite to access the tools.