EVALUATION OF CROP ROTATION AND IRRIGATION PRACTICES UNDER LIMITED WATER AVAILABILITY

Since 1991, the drought conditions in Central Oregon have seriously impacted the amount of water delivered to the North Unit Irrigation District (NUID). The objective of this economic study was to determine how irrigation practices and crop rotations should be managed in response to reduced water supplies, and how that will impact profitability. A mathematical programming model was developed to evaluate the economics of adopting such practices on a representative farm in Jefferson County. The 500-acre farm produced bluegrass seed, carrot seed, garlic seed, wheat, and peppermint, using sprinkler and furrow irrigation systems. New practices for water conservation included irrigation scheduling and laser leveling of fields, alternating furrow, and surge furrow irrigation. Assumptions were based on the fixed and variable cost, crop rotation, and water-use of farms in Jefferson county. Results showed that the adoption of water-conserving management practices can increase net returns over traditional systems. When 24 and 36 acre inches of water were available, the irrigation systems employed in the profit-maximizing solution included alternating furrow with gated pipe, surge furrow, and some traditional continuous furrow irrigation. But when available water was limited to 18 acre inches, the best returns were from surge furrow and surge furrow with a pumpback system on limited, specific crops. Finally, allocating 12 acre inches per acre took approximately one-third of the farm out of production and utilized surge furrow with a pumpback system. The affordable price of additional water, in this scenario, was determined by the model to be over ten times greater than the NUID price. Continuous furrow and wheel-line sprinklers produced lower net returns for the representative farm than implementation of alternate systems. Interestingly, the model-optimized crop rotations excluded peppermint at the present yield and price due to low net returns and high irrigation requirements. While the above results may not hold for all seed producing farms in Jefferson County, the model showed an economic incentive exists for adopting water-conserving practices