Abstract
Swine manure is readily available in Iowa and is an excellent source of fertilizer for crops. Application rates are often based on the nitrogen (N) needs of the coming year's crop. Producers often ask how much N is available the first year, and if any N carries over to subsequent years.
Abstract
Agricultural Science | Agriculture 
Introduction
Swine manure is readily available in Iowa and is an excellent source of fertilizer for crops. Application rates are often based on the nitrogen (N) needs of the coming year's crop. Producers often ask how much N is available the first year, and if any N carries over to subsequent years.
Materials and Methods
Manure has been applied to plots in a cornsoybean rotation at the Southeast Research Farm (SERF) over the past 5 years. In 2002 and 2003 plots with a lower rate of manure and where NServe was used were added. On all plots (except 4000I-yearly where manure was applied every year), manure or fertilizer was only applied ahead of the corn crop. In 2004, plots were split with anhydrous ammonia nitrogen applied to half of each plot in the fall of 2003. Nitrogen was applied at 150 lb/acre. Corn was planted on all plots in 2004. Late-spring nitrate tests (LSNT) and crop yields were collected on all plots.
Results and Discussion
The manure applied in the fall of 2001 (for the 2002 growing season) was extremely uniform with an average of 40 lb of N/1,000 gal. In Table 1 , the addition of N-Serve increased yields slightly at the 2,000 gal/acre rate but there was no difference in the LSNT or end of season stalk test levels. At the 4,000 gal/acre rate of manure, the addition of N-Serve showed a slight increase in the LSNT and end of season stalk test; however, there was no increase in corn yield with the addition of N-Serve.
Results and Discussion
Unfortunately, in the fall of 2002, the manure that was applied for 2003 was not as uniform as for previous years. One load of the manure had about 20 lb of N/1,000 gal while the remaining loads had nearly 60 lb of N/1,000 gal, causing a difference in manure N levels even with the same manure application rates. In Table 2 , treatments with equal N levels in the manure were the 4,000 gal injected every year and the 4,000 gal injected with N-Serve. In the latter case, the addition of N-Serve did show higher LSNT and end of season stalk test levels. However, with excess levels of N available to the crop already, there was no difference in corn yield. It is worthwhile noting an over 70 bushel/acre response to the first 40 lb/acre of manure N that was applied
Results and Discussion
In 2004 with corn after soybeans where no N was applied, all LSNT results were similar but deficient (less than 20 ppm). Two treatments, 8000I and 4000I-yearly, showed increased yields over the other treatments. This is likely because of N built up in the soil where more N had been applied than removed in the previous 5 years.
Results and Discussion
For corn after corn plots where no N was applied for 2004, LSNT levels were lower (9 ppm) than for the corn after soybeans plots (11 ppm). Check treatment yields with no N applications for 5 years were also much lower in corn after corn (38 bu/A) than for the corn after soybeans (121 bu/A). While there did appear to be an increase in yields with some previous manure applications, this seemed to be more a function of total N applied in past years. When comparing treatments with no additional N applied for 2004, the yields appear to show more carryover of N where N-serve was used for 2003 (Table 3) .
Results and Discussion
For both corn after soybeans and corn after corn, the previous treatments of commercial N and 4,000 gal/acre injected (both done only ahead of corn) had similar yield levels in 2004 for the same previous crop and N application.
Acknowledgments
Funding was provided by a grant from the Iowa Pork Industry Center with assistance from the Southeast Research Farm. 

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