Novel manure products may hold environmental and economic advantages

Victor Green, Director, soil health and crop sustainability, Dairy Management Inc.

A variety of novel manure products and technologies are emerging as resources for dairy farmers. Up until now, though, the effects of such products on soil health have received little, if any, field testing.

DSWR is investigating the potential environmental and agronomic benefits of these products over traditional use of liquid dairy manure. They may also offer economic advantages for farmers.

Significance to DSWR

The novel manure products used in the project are examples of biogenic fertilizers, in that they are created from a biological source. Creating fertilizer from biological sources, liquid dairy manure in this case, is a dramatic shift from the current commercial fertilizer production system that uses a highly energy-intensive process.

The new products also represent the evolving technology of nutrient separation in which nutrients are separated or reduced from the original source. This offers benefits such as greater transport efficiency, a more balanced crop nutrient application, and the potential for exporting off the farm as a revenue source.

Nutrient separation technology provides a more efficient fertilizer compared to conventional manure, which can result in overapplication of phosphorus, creating potential environmental challenges.

There are some greenhouse gas (GHG) reductions from the novel products also, which is one of the main things we are trying to quantify in our research. This is particularly true with nitrous oxide, which is a potent GHG and a major source of emissions from forage production and manure application.

Types of manure products

The DSWR project incorporates a wide range of manure products. Our research is comparing common and historical standard manures that are typically used in each of the regions to products that, in some cases, have had very little field research because the technologies are so new.

Products we are looking at in the study are liquid dairy manure (LDM), dairy compost, a flocculant product and an evaporative product. Additionally, in California, one of the treatments we are evaluating is lagoon water as both a nutrient and water source in a flood irrigation system, which is common in that region.

One of the farms participating in the study creates their own compost amendment on-farm, thus reducing their volume of manure to handle and also reducing fertilizer costs to crops. All the compost amendments used in the project are sourced locally from dairies that are composting to add another revenue stream to their existing business and help them in meeting nutrient management regulations by reducing disposal costs and enabling the export of nutrients off the farm. Not surprisingly, these are similar reasons for interest in novel manure product technology.

LDM is the traditional source of manure we are comparing to the other products. LDM has long been known for its fertilizer and soil health benefits. The downside is that it must be applied at very high rates due to its low nutrient content, consisting mostly of water, which is inefficient compared to using higher nutrient content fertilizers. Often, the LDM is more of a disposal issue. While fertilizing the crop with this nutrient source is beneficial, it is not very efficient in terms of transport, application or even balanced with the crop uptake requirements.

The flocculant products are an example of wastewater treatment technology being incorporated in agriculture. This technology can remove nearly 80% of phosphorus from the liquid source. Liquid, that is returned in the form of “tea water,” contains most of the ammonium. Since much of the phosphorus has been removed, the tea water can be applied at higher rates to better meet crop nitrogen demand.

Theoretically, with the higher nitrogen content and lower phosphorus content, the liquid applications would result in lower application rates that still meet crop needs and thus result in less tanker loads in total. The solid by-product from the process contains most of this captured phosphorus that was removed from the liquid. This enables more efficient transport to distant fields where it can be applied for crop phosphorus needs and as a valuable soil amendment. Since there is little ammonia in the solid, there is no urgency to incorporate the product with a disc, which is typically done with conventional sources of manure.

The evaporative process is also very new. This process can remove 100% of ammonia from the liquid source and create a more stable ammonium nitrate product that is not prone to volatilization and atmospheric loss. The nitrogen content of this product is currently 10%, which is immediately available for crop uptake. This product is being marketed to the organic market. It is a dramatic difference between traditional organic fertilizers, which are slow-release and more dependent upon environmental factors (temperature and rainfall) to slowly become available over time to the crop. The solid product contains the remaining nutrients and is a valuable soil amendment and fertilizer source. As with the flocculant product, it can be surface applied and not require incorporation with a disc and could lend itself to use in a reduced tillage system.

There are pros and cons to all manure sources. It should be noted that there is still work to be done to make the novel manure products more efficient and more attractive to farmers.

Application of the products

The products are being applied with either a standard flail manure spreader or typical commercial scale fertilizer spreaders. At our smaller sites, it is spread with a Gandy fertilizer spreader commonly used in fertilizer studies. It has even been spread by hand on one of the smaller trial sites, which is obviously very labor intensive.

The novel manure products are featured as a component of a soil health management system, which may be no-till, strip-till or limited tillage along with a cover crop. In this system, the products are not typically incorporated into the soil with a disc, as is usually the case with most manure applications. The products are surface applied and remain on top of the soil to avoid soil disturbance. These products offer advantages over LDM in conservation systems because they are more environmentally stable, not susceptible to as much volatilization and have reduced GHG emissions, at least theoretically, which is due to the nutrient separation and reduced ammonia.

Economic implications

The novel manure products offer potential marketing opportunities to export the products off farm. Ideally, this would be to a region with limited phosphorus and a large demand, such as the Corn Belt. The reality is that high moisture content presents logistical and economic constraints. This has also been a challenge with compost.

Co-products from the evaporative process are in the liquid and solid form. The liquid is now being marketed as ammonium nitrate. A few decades ago, ammonium nitrate, in its solid form, was a popular fertilizer but became increasingly regulated due to its high flammability and was expensive compared to other forms of fertilizer. The liquid form is low in flammability and is easy to transport and apply in the field. Its nutrient content (10% nitrogen) is considered high compared to most organic fertilizers and immediately available to plants.

Evaporation and flocculation manure products do require large capital expenses and are currently for large dairies only. It should be noted that these technologies can significantly reduce traditional environmental impacts from manure and can help farms achieve regulatory compliance easier and lower their carbon footprint.

Early effects

At this time, we have not seen any significant changes to soil health from any of the products as compared to the LDM. This should not be too surprising given that all of the treatments in the project (LDM, compost and novel products) are supplying all of the nutrients required by the crop and are already known to benefit soil microorganisms. One of the fundamental tenets of soil health is adding animals to the land. Through historic applications of manure, we are essentially doing the same thing. It is also possible that more time is needed to quantify these changes in the system.

Some of our research has shown initial yield reduction in the soil health management systems using the novel manure products or compost; however, that is likely due to compaction and not necessarily the manure products themselves. Recently, yield has seemed to stabilize in most of our research, where there is no difference between the systems.

In terms of GHG emissions, it may be a bit early to speculate until more data is analyzed.

The biogenic fertilizers derived from manure represent a very exciting technology and offer a lot of promise, though there are many obstacles to overcome. This is normal with any new business or technology.

Nutrient separation offers unique possibilities for nutrient management which will be helpful for water quality and environmental reasons. These are frontier technologies that may offer tremendous benefits to agriculture in the future as the industry strives to not only produce nutritious dairy products but also to be more environmentally and economically sustainable.