Corn Production as Affected by Time and Rate of Manure Application and Nitrapyrin

Maximum manure N use efficiency by corn (Zea mays L.) requires that N mineralization and subsequent plant availability coincide with N uptake demand. Information regarding the effects of time of manure application and use of a nitrification inhibitor on manure mineralization and corn yield is needed for producers to make sound manure management decisions. Studies were conducted at seven southern Minnesota sites over 3 yr to determine the effects of three manure application times (mid-September, mid-October, and late April), two manure rates, and a nitrification inhibitor, (nitrapyrin [NP] 1.0 lb a.i./acre), on corn yield and soil nitrate N concentration (0 to 12 in.) at the V4 growth stage. Application rates ranged from 3000 to 4000 gal/acre for the low rate and from 6000 to 8000 gal/acre for the high rate. For the four sites receiving liquid dairy (Bostaurus) manure, soil nitrate N was greatest when manure was applied in April and lowest when applied the previous September. The addition of NP increased soil nitrate N at three sites but affected grain yields at only one site when averaged across time and rate of manure application. Grain yields for the April, October, and September applications averaged 146, 142, and 139 bu/acre, respectively, across manure rates and NP treatments, with April exceeding the September application time (P < 0.10). When liquid swine (Sus scrofa domesticus) manure was used, the effects of application time and NP on soil nitrate N concentration and grain yield depended on climatic conditions. At one site where 8.5 in. of rain fell in a 5-wk period in the spring, NP significantly increased both soil nitrate N concentration and grain yield for the October application but had no effect with the April application. Similar effects of NP on soil nitrate N were found at the other sites, but grain yields were not increased. Results from the seven site-yr support about a 5% yield increase with April application compared with fall applications. However, it is unlikely that many farmers will consider this an economic advantage because of logistical challenges often faced with spring applications of manure in the Northern Corn Belt. Research QuestionOptimizing the use of N from manure requires that mineralization and subsequent plant availability of N from the manure coincides with plant uptake. Time of manure application (fall vs. spring) and use of a nitrification inhibitor are management decisions facing farmers that may greatly affect the agronomic value of manure and associated potential environmental risks. In this study, we determined the effect of three manure application times, two application rates, and the use of nitrapyrin (NP) on soil nitrate N concentrations at the V4 growth stage and corn grain yield. Using both dairy and swine manure, our hypothesis was that corn yields would probably be greatest with spring application of manure and with the addition of NP to fall-applied manure. Literature SummaryResearch conducted in areas where soil temperatures generally remain above 32°F during the winter showed higher yields and uptake of N from spring-applied manure than with fall applications. On the other hand, fall application of solid dairy manure in Wisconsin was superior to spring application when spring weather was wet and cool. Adding NP to manure has shown inconsistent results with positive responses when used with fall-applied swine manure in Indiana and no response with spring-applied liquid dairy manure in Wisconsin. Study DescriptionField studies were conducted at seven locations during a 3-yr (1993–1995) period in south-central Minnesota. Soil texture of the mollisols ranged from silt loam to silty clay loam. Oats, soybean, and millet were the previous crops, and irrigation was not used. Soil test P and K levels were high to very high and should have precluded any response to these nutrients. Liquid dairy manure was applied at four sites with three sites receiving liquid swine manure. Targeted times of application were mid-September, mid-October, and late April. Two application rates (low = 3000 or 4000 gal/acre and high = 6000 or 8000 gal/acre) were sweep-injected about 4 to 5 in. deep. Nitrapyrin at a rate of 1 lb a.i./acre was added to one-half of the manure treatments. Fertilizer N as urea was applied in the spring at rates of 0, 50, 100, and 150 lb N/acre. All treatments were replicated four times in a randomized, complete-block design. Soil samples were taken from the 0 to 12-in. depth at the V4 stage and analyzed for nitrate N. Com grain yields were determined by combine harvesting. Applied QuestionsDid time of manure application influence soil nitrate N concentration at the V4 stage and corn grain yield? Soil nitrate N concentration was generally greatest when dairy manure was applied in April and lowest for the September application. Grain yields were about 5% higher for April application than for fall applications. When swine manure was used, response to application time was highly dependent on spring and early summer weather. Under wet conditions, April application of manure gave substantially higher nitrate N concentration and grain yields compared with October application. When weather was more normal, soil nitrate N was greater for April application, but grain yields were unaffected by application time. Averaged across the 7 site-yr, grain yield from fall manure application was about 7 bu/acre less than from spring application. However, because of logistical challenges, i.e., soil compaction, timeliness issues, inadequate manure storage capacity, etc., it is likely that many farmers in the Northern Corn Belt will not consider this an economic disadvantage. Was NP effective at increasing soil nitrate N concentration and grain yield? The addition of NP to manure increased soil nitrate N at five sites but only increased grain yield at two sites. At the site where 8.5 in. of rain fell in a 5-wk period during May and June, grain yield was increased 16 bu/acre when manure plus NP was applied in October but was not affected by NP when applied in April. Did the in-season soil nitrate test at the V4 stage serve as a good predictor of N availability from the manure? Based upon published current standard critical levels (above which no fertilizer is recommended), pre-sidedress nitrate soil testing did not adequately predict N supply to corn from manure that had been applied within 8 to 9 mo prior to soil sampling. This was especially true for dairy manure. RecommendationsFall application of liquid dairy and swine manure, when soil temperatures have cooled to about 50°F or less, provides an agronomically acceptable alternative to spring application for the livestock producer. Although the addition of NP did not give conclusive results in our studies, soil nitrate N concentration was often increased by NP, and under wetter-than-normal spring conditions, yields were improved when NP was added to fall-applied swine manure. These data suggest that NP should be considered when applying recommended rates of liquid swine manure before soils have cooled to remain below 50°F.