Injecting manure has been shown to increase N available for a following crop (reduce ammonia loss), improve neighbor relations with reduction in odor, and reduce likelihood of manure runoff during intense rainfall and rapid snow melt.
Manure injection has been studied extensively at Penn State and at numerous other land grant universities since the early 2000's. More specifically, the research in recent years has focused on low-disturbance manure injection, frequently called shallow disk injection, which has been shown in research to be compatible with no-till cropping systems. When compared to broadcasted manure, injected manure reduces volatile losses of ammonia and other objectionable gases by up to 90%. Ammonia in liquid manure can be 30 to 50% of the nitrogen (N) in the manure. Also, due to increases in the amount of crop-available N when manure is injected, nutrient management plans will require a reduction in manure application rates. This will also result in fewer pounds of P being applied per acre, reducing the potential for soil P levels to become excessive in crop rotations where P removal by crop harvest is less than the amount being applied in manure. Additionally, manure placed under the field surface reduces the potential for manure and the nutrients in it to be carried into surface waters when rainfall is heavy and snow melt is rapid. Manure injection results in a marked increase in the amount of manure N available for future crop use, while improving neighbor relations due to large reductions in manure odor. However, specialized equipment must be added to manure tankers, and the process of injecting manure is somewhat slower than broadcasting. Both factors will increase the cost of manure spreading. However, if N is limiting on the farm, research has shown that the savings in N fertilizer required when manure is injected, can offset some, if not all of this additional cost.
Penn State Extension was awarded an NRCS Conservation Innovation Grant during the early 2010's which included on-farm comparisons of broadcasted and injected manure. The study included replicated plots on two farms in each of 3 southeast PA counties during each of 3 years. Most were dairy farms. Fields on which the studies were conducted received regular applications of manure, with many being manured during both the spring and fall hauling seasons. In our trials, where corn for silage or grain was grown, rates between 4000 and 7000 gallons of slurry were routinely applied to both treatments on a given field. Corn silage or grain yields were measured at harvest. Seldom did we document an increased yield where manure was injected. While slight to moderate droughts at many locations during two of the three years contributed to this lack of response where more N was available in the injected manure plots, we determined that the extensive manure history on many of these fields resulted in an accumulation of soil organic N; that is, there was already more than enough N to meet crop needs and the "extra" N from the injected manure was of little or no benefit. Yes, odor was reduced, neighbors were happier, and more N was available to succeeding crops, but are those benefits enough to offset the increased cost of injection equipment and the slightly greater time required to inject the same amount of manure? Limited farmer and hauler interest in manure injection at that time indicated to us that the answer was no!
Red Barn Consulting in Lancaster conducted a survey of 41 farms they believed would be good candidates for manure injection. Of the 41 farms surveyed, 13 farms (32%) indicated that they were interested in trying manure injection. However, the remaining 68% of farms did not indicate that they were uninterested. Half of the remaining (14 farms or 34% of the total) weren't as positive as the first group, simply because they believed that trying injection would be difficult because they were unaware of haulers equipped with manure injection equipment. The above two groups represent nearly 2/3 of the respondents who have interest in at least trying manure injection… if the equipment is available. This amount of interest was surprising to us. Do an increasing number of PA farmers see manure injection as a way to:
- Apply nutrients under the field surface so as to minimize loss during runoff events?
- Apply nutrients under the field surface without resorting to full-width tillage to incorporate broadcasted manure?
- Maintain continuous no-till production systems and enjoy the benefits of that system?
- Improve neighbor relations at the farm/suburban interface?
- Accelerate the rate at which PA can keep nutrients and sediment out of our waters (and possible increased regulations from being enacted that negatively impact our farms?)
Penn State extension has teamed up with Sustainable Chesapeake to secure funding for a project that further investigates the potential to increase manure injection on PA farms. Survey results (above) and some early feedback from a continuing injection demonstration project in Maryland seem to indicate that farmers are more receptive to this technology at this time. Several commercial manure haulers who service Lancaster, Lebanon, and surrounding counties have expressed interest in participating. Farmers who hire custom haulers are encouraged to ask haulers if they offer, or are considering offering, manure injection as an option.