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Effects of Soil and Nitrogen on Water Use Efficiency of Tall Fescue and Switchgrass Under Humid Conditions

USDA-ARS, U.S. Regional Pasture Research Lab., Curtin Road, University Park, PA 16802

* Corresponding author.

ABSTRACT

Nitrogen fertilization of semiarid grasslands interacts with available soil moisture to increase forage yields and water use efficiency of grasses. If interactive effects of water and N can be determined under humid conditions, increased production could be realized on the droughty, hill land pastures of the northeast USA. The objective of this study was to quantify the interactive effects of N fertilization and soil water availability on the yield and water use efficiency of a C₃ and a C₄ forage grass under humid conditions. Tall fescue and switchgrass were grown on three shale derived soils with available water holding capacities of 25, 15, and 5 cm. The grasses received 0, 90, and 180 kg ha^–1 of N. The N was applied in a split application on fescue and in one application on switchgrass. Grasses were harvested at early heading and in late fall. Precipitation, temperature, and soil water data were recorded throughout the growing season. During years when precipitation was evenly distributed, N was the main factor controlling yields and water use efficiency, accounting for about 80% of the variation in those two parameters. When most of the precipitation occurred as large storm events or when precipitation was low or poorly distributed, soil water holding capacity was the major factor controlling yield and water use efficiency, accounting for about 40% of the variation in the yields of tall fescue and switchgrass. Over years, water loss due to deep percolation and/or runoff was the most important soil related factor affecting yield and water use efficiency.

Contribution no. 8707 of the U.S. Regional Pasture Research Lab.

Received for publication May 14, 1987.