Methods and Economics of Drainage Reduction through Improved Irrigation

Abstract

Drainage reduction through improved irrigation is needed for addressing the problem of drainage water disposal in the San Joaquin Valley in California. Options for improving irrigation include improved management of existing systems (irrigation scheduling, duration of water applications), upgrading traditional surface irrigation systems (reduced field length, increased unit flow rate, surge irrigation, furrow compaction, tailwater recovery), and converting to pressurized irrigation systems (hand‐move and linear‐move sprinklers, low‐energy precision application (LEPA) machines and rip irrigation). The most effective upgrade of surface irrigation systems for reducing subsurface drainage is a reduced field length coupled with reduced irrigation times. Increased furrow flow rates resulted in little change in drainage in some cases. Surge irrigation offers an opportunity of reducing subsurface drainage by only about 1/3. Converting to pressurized irrigation methods can substantially reduce subsurface drainage, but may be uneconomical in some cases. Analyses of large‐scale field comparisons of irrigation methods revealed that generalizing about the best irrigation method is difficult. Economic analyses of these comparisons showed a well‐managed furrow system to be more profitable than a subsurface drip system in one case, but a subsurface drip system to be more profitable compared to a marginally managed furrow system in another case. The analyses also revealed that disposal costs of subsurface drainage water may need to be much higher than projected costs to economically justify converting from furrow irrigation to irrigation systems with high capital costs.