J.L. Paul

The foliar absorption of urea‐N by tall fescue and creeping bentgrass turf

Abstract The absorption and assimilation of 15N‐labeled urea applied to the foliage of tall fescue (Festuca arundinacea Schreb.) and creeping bentgrass (Agrostis palustris Huds.) turf was examined under a controlled environment. Each source of N was dissolved in deionized water to a final concentration of 25 g N liter‐1 and spray‐applied at a rate of 5 g N m‐2. Absorption of the fertilizer‐N over a 72 hr period, as measured by 15N analysis of tissue digests, averaged 55% for the two species. Absorption was also estimated by a washing procedure which measured the urea remaining on the foliage, and by the increase in total N in the plant tissue. There were no significant differences between the three methods in estimating absorption. Partitioning of the absorbed 15n between tissues averaged 37% in new leaves, 51% in old leaves and shoot tissue, and 11% in the roots. More than 90% of the absorbed urea‐N was hydrolyzed by 72 hr.

Volatilization and rapid depletion of urea spray-applied to Kentucky Bluegrass turf.

Abstract Urea was spray‐applied to a Kentucky bluegrass (Poa pratensis L) turf at a rate of 50 kg N ha‐1. Two volumes of solution were used to provide application depths of 0.5 and 2.0 mm. Ammonia volatilization and the rate of disappearance of the applied N were then examined over a 48 hr period. Urea‐N was positioned primarily on shoots with the 0.5 mm application, whereas the 2.0 mm application distributed the urea equally between the shoot and the thatch/soil layers. Urea positioned in the thatch/soil was hydro‐lyzed rapidly, while very little hydrolysis occurred with the urea positioned on the shoots. Cumulative volatile loss amounted to 5.3% and 11.6% of the applied N with the 0.5 and 2.0 mm application, respectively. Applied urea‐N disappeared rapidly from the turf/soil system. Approximately 80% and 100% of the applied N was depleted by 48 hr for the 0.5 and 2.0 mm application, respectively. The duration of volatile loss was correlated with the period that the urea‐N was resident in the turf profile.

Nitrogen Critical Level Determination in The Woody Ornamental Shrub Euonymus fortunei

ABSTRACT We determined the critical nitrogen (N) level on greenhouse-grown winter creeper (Euonymus fortunei Hand. Mazz. ‘Colorata’) in one-gallon containers by adding N in doses of 0 to 400 mg/pot as ammonium nitrate (NH4NO3) and growing plants for 50 days without leaching. At harvest, leaf N concentrations were similar in all treatments up to 150 mg/pot, but increased with applied N above 150 mg/pot. Yield increased with increasing leaf N up to about 1% N, but was relatively constant at higher leaf N. The leaf N critical level was 1.03%. Shoot:root ratio, based on new growth, decreased with applied N. This method for critical level determination provides an accurate description of the relationship between leaf N and growth and may be used by growers to improve fertilizer use efficiency.