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Fluid Journal : Fluid Journal 2005-2007
Early Spring 2006 Fluid Journal 2 alfalfa producers, no significant treatment differences in either yield or N removed were apparent. All estimated NUE registered less than 18.6 percent. The application of dolomitic limestone Figure 1. Analysis of variance by treatment means on total alfalfa dry matter yield, five-year study, Lahoma, OK. Figure 2. By-harvest alfalfa dry matter yield differences for treatments receiving (A) 10 or (B) 20 lbs/A of N following each harvest compared with the check (no N application) for 24 harvests, five-year study, Lahoma, OK. did not produce a significant response in yield or N removal. Similarly, the initial soil pH was relatively high (7.2) at this site, although no significant response was found either by harvest or across years. Bottom line Significant yield increases as a result of applying N immediately following harvest were detected on only three of 24 harvest dates (Figure 2). For these three dates, yield increases (percentage of check yield) ranged from 17 to 26 percent. These increases all took place in either the last or second to last harvest. For growing periods encompassing the three dates where we observed significant increases in yield, rainfall received since the previous cutting ranged between 2.2 and 3.6 inches and was generally evenly distributed across the 30- to 40-day growing periods. For some of the growing periods much higher than normal rainfall (greater than 7.9 inches) was received during relatively short periods of time. Although single-harvest yield increases in excess of 0.18 T/A (360 lbs/ A) were observed on several dates, treatment variability was high, thus reducing the number of significant responses. Using a price of $100/T for alfalfa, current N prices of $0.45 per lb of N and an increase of around 0.18 T/A, low rates of N (20 lbs/A) applied prior to late cuttings could produce a positive return on investment ($18 of hay value for $9 of applied N). However, applying N as low as 10 lbs/A after every cutting over the 5 years of the study resulted in net losses even at N prices 40 percent (28 cents/lb of N) less than current levels. Excluding the first year of the study, forage N tended to decline from the second to the fifth harvest. Studies have attributed this to a seasonal decline in N2 fixing capacity of the alfalfa plants. The three significant yield increases as a result of applying N took place in either the last or second to last harvest.
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