Iowa livestock producers managing drought-stressed pastures wanted to know if grass-based pastures would recover more quickly or produce more forage by applying nitrogen to pastures in the fall versus their traditional spring application management. A pasture fertilization study was conducted on cool-season grassbased pastures at the Iowa State University Armstrong, Neely-Kinyon, and McNay Research and Demonstration Farms. Urea was hand applied at rates of 0, 22.5, 45, 66.7, and 90 lbs/acre to small plots at each site in October 2000. Some plots received 22.5 and 45 lbs/acre of N at the fall application date as the first half of a split application to total 45 and 90 lb/acre of N. The same N rates were applied to different plots and the remainder of the split application treatments was applied in March 2001. Dry matter yield was determined in mid-May 2001. Yields at the Neely-Kinyon and McNay farms were similar, and slightly higher than those at the Armstrong farm. Yield response to nitrogen application rates was positive and linear for each additional unit of nitrogen applied. The average total increase was about 38% for the first 45 lbsN/acre and about 81% for the 90 lbN/acre rates. There was no statistically significant or consistent relation between pasture yield increase and timing of nitrogen application across the three sites, but there were minor differences among sites. The trend, however, indicated that greater yields frequently were obtained from the early spring application treatments.
Data was not collected to assess forage nutritive quality or stand density, however, both could be of value and importance to the long-term sustainability of a foragelivestock enterprise. These results indicate that for the period studied, there was no consistent advantage in applying nitrogen fertilizer to grass-based pastures in late fall or splitting the total application between fall and spring as compared to making traditional spring nitrogen applications
