Animal manure is a source of plenty essential macro and micro plant nutrients required for crop production. The increasing number of large livestock operations in Saskatchewan is providing local producers with valuable liquid manure from these barns. Liquid swine manure is low in nutrients per unit volume relative to commercial fertilizer. This dilute form of nitrogen needs to be applied to the soil in high quantities usually greater than 3000 gallons per acre (GPA).
An area of concern for hog manure application is the contamination of ground water with nitrates as a result of large quantities of nitrogen added to the soil. Studies to address this issue were done by the ECRF located at Canora. Liquid hog manure was injected in the spring of 2000 by PAMI (Prairie Agricultural Machinery Institute) out of Humboldt who came out with an injection truck. The hog manure treatments were applied at rates of 3000, 6000, and 9000 GPA from a hog finisher barn. Plots were seeded in year 1, to Metcalfe barley and canola in year 2. Aside from the hog manure treatments, there were also plots seeded using three different rates of granular nitrogen fertilizer (46-0-0) at rates of 50, 100, and 150 lbs of actual N/acre. The granular fertilizer plots received 25 lbs/acre P, and 15 lbs K/acre in addition to the N. There was also a summerfallow plot and an unfertilized check. Yield data was taken from the plots and soil testing was done on the different treatments to determine how much nitrate remained in the soil and to see if it was moving downwards through the soil profile. The analysis of the manure, applied to this study, indicated nitrogen levels of 33 lbs of N per 1000 gallons, this translates into approximately 100, 200, and 300 lbs/acre for the 3000, 6000 and 9000 GPA treatments, respectively.
Table 1 clearly illustrates that the nitrates in year one of the study were higher for the 6 and 9 thousand gallon rate when compared to the commercial fertilizer for the 0" -12" sample. It is also interesting to note that the summerfallow treatment at this depth was just as high as the 6000 GPA rate. The higher nitrate seen in the summerfallow is due to the fact there was no crop to utilize the available nitrogen. The samples taken from year 2 of the study show that the nitrate level of the manure treatments are not significantly higher when compared to any of the other fertilizer treatments for the 0" - 12" sample. The samples, in year 1 and 2, show no significant difference of nitrates in the cores obtained at depth 12" - 48". This data indicates the nitrates tend to stay in the upper portions of the soil profile, suggesting there is little chance of ground water contamination occurring from this application. It is important to realize that the fate of nitrates in soil depends upon the soil properties. Different types of soil may require different management practices that may allow for higher or lower safe application rates.
It takes intense planning to manage manure as a fertilizer properly. One of the biggest concerns when dealing with manure is the amount total nutrient composition and the available nutrient composition. Nitrogen (N) is usually the biggest concern because it is used by plants in the highest quantity. Depending on the type of operation the manure is obtained there is different nitrogen concentrations. Manure from a hog finisher barn, for example, ranges from 15-50 lbs total N per thousand gallons of product. Nursery and farrowing barns contain lower concentrations than finisher barns. The concentration of N is also dependent on the type of storage facilities where the manure is stored. Of the total N in liquid swine manure about 50% - 90% is in the plant available form of ammonia NH4. The remainder of nitrogen is in the organic form and needs to undergo the process of mineralization to become inorganic and consequently plant available.
Phosphorous is another macronutrient that is present in hog manure. The concentration of phosphorous present in manure is directly related to the amount of solids present. As the amount of solid material increased in the manure sample, the higher the amount of total phosphorous. Common phosphorous levels of liquid swine manure range from 2 - 40 lbs of P2O5 per 1000 gallons. The availability ranges from 10% - 50%.
Potassium (K) in manure is readily available for use by plants. The concentration of K is similar to Nitrogen at 8 - 20 lbs/1000 gallons. Liquid hog manure is known to be on the low side for sulfur. Crops demanding high amounts of sulfur may require additional S.
Manure is also a source of micronutrients such as copper, zinc, and boron. The research in micronutrients is not very extensive compared to macronutrients. An efficient way to test for micro nutrient deficiencies is tissue testing.
Manure is an excellent source of essential nutrients but also the organic fraction of the manure increases the soil organic matter of the soil that increases the soils tilth and nutrient supplying power.
Nutrient response data was obtained from the same plots as the nitrate study. The yields obtained from the nitrate study are illustrated below (Figure 1). The yields of barley in year 1 were slightly lower for 6000 and 9000 GPA treatment relative to the commercial fertilizer and 3000 GPA applications. This was due to the effects lodging had on the crop. It is important to note that when applying high rates of nitrogen, either manure or commercial N, the proper variety of crop should be selected. The proper cultivar sown in the first year after application should have properties of short straw, high yield potential and good straw strength to reduce lodging potential.
The yield response is quite significant in year 2 and 3 of the study for canola and barley, respectively. There was no fertilizer of any kind added in year 2 or 3 of the study. The yield response is a consequence of residual nutrients from the first year of application.
Another study conducted at ECRF was done using different manure application dates. Manure was injected either in fall or spring. The trend was toward an increased yield for the applications made in the fall. The reason could be there is more time in the spring for mineralization of the organic N.
The use of liquid hog manure is quite attractive to producers from an economic perspective. The available (inorganic) nitrogen, used in the studies discussed, has a value of approximately $8.40/1000gal. This translates into an amount of $75/acre for the 9000 GPA treatment. The manure is worth much more than this because this does not include P, K, S, micronutrients, or organic nitrogen.
Big Sky Pork is a big player in the Saskatchewan Hog industry and as such has the ability to supply local producers with liquid manure. Big Sky charges $15/acre for any amount of hog manure that is safe to apply. This cost is very low considering there is a yield response 3 years after the application and the cost for this amount of nutrients from commercial fertilizer is in excess of $100/acre. Big Sky Pork has the ability to supply liquid swine manure within a 4-mile radius of their storage facility. The manure is pumped to the field of application and once at the field, a special drag hose is coupled to an injector system. The manure is knifed into the soil using a 20-foot injection system. Applying manure on a stubble field allows more liquid to be applied per acre than a tilled summerfallow field. The minimal till system has higher moisture holding capacity and therefore more product is absorbed and less is left sitting on the soil surface. Injecting manure into the soil effectively manages odor and surface runoff, while minimizing the loss of valuable nutrients to volatilization. As much as 30% more nutrients can be lost if the manure is surface applied compared to injected.
It is important to realize that hog manure should not be viewed as a waste, but rather an economic and environmentally sound nutrient source when managed properly.