Wednesday, 9 November 2005
6

Alfalfa Cutting Schedule and Variety Interactions—Understanding the Yield-Quality Trade-off.

Daniel Putnam1, Steve Orloff2, and Larry Teuber1. (1) University of California, Dept. of Plant Sciences, Mail Stop-1, One Shields Avenue, Davis, CA 95616-8515, (2) University of California Cooperative Extension, 1655 S. Main St., Yreka, CA 96097

Yield is frequently the only criteria for alfalfa variety selection, but quality has taken on increased economic importance in recent years. Quality factors may constitute as much as 1/3 the value of the crop in alfalfa hay markets. Variety selection may also depend upon the harvest schedule imposed. Field studies were conducted over 3 years at Davis, California (a Mediterranean environment) to examine the interaction between cutting schedules (8, 7, and 6 cuts/year) and 18 varieties with a wide range of Fall Dormancy (FD) ratings. Cutting intervals varying from 24 days to 33 days between harvests had a stronger influence on quality and seasonal yield than did variety. However, results indicated a powerful influence of Fall Dormancy (FD) rating of the variety on both yield and quality. Fall Dormancy explained 80% or greater of the variation among varieties in forage quality. Varieties with very little fall growth (FD 2-4) produce lower fiber (approximately 25 g kg-1 Neutral Detergent Fiber) and higher protein forage than nondormant varieties (FD 8-10). However, forage yields were almost always lower for the more dormant varieties. These studies revealed a yield-quality tradeoff with alfalfa varieties strongly driven by differences in FD ratings. The average yield penalty for each unit of FD ranged from about 0.7 to 1.3 Mg ha-1 per year per unit FD in these studies—total annual yield differences was as much as 7.8 Mg ha-1 between some varieties. Choice of higher quality varieties did not reduce the negative effects of late cutting schedule on quality. Forage quality potential of alfalfa varieties should not be viewed in isolation from their yield potential; economic approaches to this question are suggested. Understanding the yield-quality tradeoff is essential to analyzing the economic sustainability of alfalfa.

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