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Alfalfa Water Use and Production on Dryland and Irrigated Sandy Loam¹

Field studies were conducted during a 4-year period to determine "Vernal" alfalfa (Medicago satva L.) dry matter yield in response to irrigation and fertilization variables. In the Northern Great Plants alfalfa forage production contributes significantly to overall agricultural land use; consequently optimization of resources use is desirable. Limited available information has created a need for such research.

This study was carried out on a Maddock sandy loam soil, a member of the sandy, mixed frigid Udorthentic Haploboralls. Four irrigation levels, ranging from dryland to excessive irrigation, were established as whole plots in a randomized block, split plot design. Eight different fertilizer treatments of P, K, and S were applied to split plots during the 1st year of the study. Under a three harvest per season management system dry matter yield was significantly affected by harvest number and irrigation treatment each year. Within the dryland and deficient irrigation treatment by year, yields decreased with each cutting; with optimum and excessive irrigation, yields varied inconstantly with cutting; yields increased 14 to 330% over dryland by increasing irrigation applications. Total seasonal crop water use, or evapotranspiration (ET), was determined using a water balance approach. Drainage (DRAIN) was calculated, using flux gradients calculated from tensiometer data, and appropriate soil properties. Other inputs, including irrigation (IRR), growing season precipitation (PPT), and soil water depletion (DEPL), were measured. In addition, water use efficiency (WUE) was calculated by treatment by year. Multiple linear regression analyses were used to relate actual dry matter yield (YIELD) and relative yield (RELV) to several independent variables. When plant water stress existed throughout the growing season, RELY correlated with relative evapotranspiration (RELET) in a near perfect, linear manner. Under nonstress conditions IRR, PPT, and DEPL required consideration to attain nearly perfect correlation of RELY with RELET. The results of this study indicate that under plant water stress conditions, alfalfa dry matter yield is a linear function of plant water use.

Key Words: Evapotranspiration • Water use efficiency • Irrigation • Alfalfa yield • Response functions

² Assistant professor, Dep. of Soils, North Dakota State Univ., Fargo, ND 58102; former professor, Dep. of Soils, North Dakota State Univ. (currently research scientist, ARS-USDA, Mandan, ND 58554); associate professor, Dep. of Soils, North Dakota State Univ.; former associate professor, Dep. of Soils, North Dakota State Univ. (currently associate professor, Soil Sci. Dep. North Carolina State Univ., Raleigh, NC 27607).

Received for publication March 3, 1977.