Proceedings of the Sixth International Conference on Precision Agriculture and Other Precision Resources Managemen on CD-ROM | Robert,P.C. et al., (Ed.), American Society of Agronomy/Crop Science Society of America/Soil Science Society of America,Madison, WI, 2003, USA, 2095 pp. Price: US$14.00.CD-ROM

The objective of this paper is to examine the impacts of terminating rice [Oryza sativa] irrigation earlier than usual. One straightforward result of this would be the associated cost savings (≈$10 ha⁻¹ per irrigation or more with deep wells) without placing a value on the water itself. However, another option exists for some farms. An assumption is that the typical farm will be constrained from irrigating all of the soybean [Glycine max (L.) Merr] crop due to constraints in any or all of water supply, pumping capacity, and labor availability. In these cases, a portion of the land in soybean production would be non-irrigated for the first part of the growing season. This study explores the possibility of transferring irrigation water to the soybean crop after the needs of the rice crop are met. If rice and soybean planting dates are planned optimally, this partial irrigation can lead to substantial soybean yield improvements and therefore a more profitable rice/soybean production system. On average, across a 41 year period, net revenue gains from partially irrigating the soybean crop were consistently positive, ranging from $41 to $458 ha⁻¹. While these numbers are interesting, the reader is cautioned that the results are based on simulation models and therefore the marginal analysis results are more realistic. On clayey and silt loam soils at Keiser and Stuttgart, respectively, the change in returns for moving from the least to the most water saving rice irrigation strategy was $190 and $99 ha⁻¹, respectively. In addition, for any given year, financial losses are typically restricted to the irrigation setup costs of $17 ha⁻¹. The irrigation termination strategies therefore show high economic potential with little risk of loss.