The fate of urea applied to Kentucky bluegrass (Poa pratensis L.) turf was studied over a 2-yr period using a combination of intact monolith lysimeters and small plots. Soil type was a Marlette fine sandy loam (fine-loamy, mixed mesic Glossoboric Hapludalfs). Urea was applied at a rate of 196 kg N ha-~ yr-~ in five equal applications of 39.2 kg N ha-i, using two application schedules. Treatments were fertilized at approximately 38-d intervals with the "Spring" treatment fertilized from late April through late September and the "Fall" treatment from early June through early November. In 1991 only, the April and November applications used tSN-labeled urea (LFN). For the Spring treatment, 31% of LFN was recovered from thatch at 18 DAT. This value remained constant for the next year, then gradually declined to 20% after 2 yr. Only 8% of the LFN was recovered from soil at 18 DAT and increased to only 20% 2 yr after application. Approximately 35% of the LFN was harvested in clippings over 2 yr. Through May 1993 (748 DAT), LFN in leachate totaled 0.18% of the amount applied. For the Fall treatment, 62% of the LFN was recovered from thatch at 18 DAT. This value declined to 35% by the following June. LFN in soil increased from 12% to25% over 2 yr. Approximately 38% of the LFN was harvested in clippings over 2 yr. Total leachate LFN recovery was 0.23% over the 2-yr period. Total recovery of LFN was 64 and 81% for the Spring and Fall treatments, respectively, suggesting volatile losses of N. Whether the N was applied in the spring or late fall, rapid uptake and immobilization of the LFN resulted. A maximum of 25% of applied LFN was recovered in the soil from either application timing at any time over the 2 yr of the experiment. A well-maintained turf intercepts and immobilizes LFN quickly making leaching an unlikely avenue of N loss from a turf system. L TE FALL (early to mid-November) N fertilization cool season turf has been recommended for many years. Wilkinson and Duff (1972) induce a growth or color response through the winter, but plants had higher chlorophyll contents and enhanced growth and color in mid-April compared with plants fertilized earlier in the Fall. These characteristics are desirable in turfgrass culture. However, leaching of fertilizer nitrogen (FN) applied to turf has received much attention in recent years, and the fate of late fall N applications may be of special concern due to slow growth rates and potential lack of plant uptake.Studies of N fate under turf management conditions are limited; however, investigations into certain aspects of N fate such as leaching or plant uptake are more plentiful and have recently been reviewed by Petrovic (1990). Starr and DeRoo (1981), using a Kentucky bluegrass-red fescue (Festuca rubra L.) turf, observed that where clippings were not returned, total N removed during mowing averaged 95 kg ha -~ yr -~ over three years, equivalent to 50% of the FN applied. Where clippings were returned, harvested N averaged 137 kg ha -~ yr -~ (73% of applied FN). By u...

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in small lysimeters. Can. J. Soil Sci. 58: 39-51.The influence of rate of fertilizer N and soil moisture on N uptake by spring wheat, N mineralization, A-values and N recovery was determined in small lysimeters on stubble land by means of 15N-labelled KNO3. Net rnineralization was enhanced by frequent irrigations but depressed by cropping. In contrast to most growth chamber results, N uptake was not linearly but logarithmically related to rate of application; uptake from fertilizer was positively related to rate, but only up to a point beyond which it levelled off; uptake from native soil N was generally negatively related to rate; A-values were not constant but negatively related to rate except at the highest rates (123-164 kg N/ha) when they were positively relared especially under dry conditions. These differences in results were credited to the fact that the RESULTS AND DISCUSSION