Irrigating forage crops with saline waters; 1, Volumetric lysimeter studies

In regions lacking outlets for agricultural drainage disposal, the recycling of drainage waters for irrigation is increasingly seen as a viable management option. Vadose zone modeling could potentially assist in the design of management practices for drainage reuse operations, but data are lacking about the accuracy of simulations of root water uptake under the dynamic, saline field conditions that are encountered in reuse systems. This study used a volumetric lysimeter system to examine, within the context of drainage reuse management systems, relationships between irrigation water salinity, irrigation depth, forage crop biomass production (alfalfa [Medicago sativa L.] and tall wheatgrass [Agropyron elongatum (Host) P. Beauv.]), ET (evapotranspiration), drainage depth, and drainage water quality. Findings include: (i) ET rates in the volumetric lysimeters were very high owing to clothesline and oasis effects; (ii) the relationship between ET and yield differed from what has been reported in the literature, possibly due to higher evaporation rates in abundantly watered, salt-stressed treatments that had reduced canopy cover; (iii) the salt tolerance exhibited by tall wheatgrass was significantly lower than what has been reported in the literature, whereas the salt tolerance of alfalfa was found to be in reasonably good agreement with reported values; (iv) leaching fractions varied greatly in response to both irrigation depth and irrigation water quality; and (v) drainage water quality and depth varied in response to temporal variations in evapotranspiration. In a companion study, the data were evaluated against a simulation model considered for use in the design of reuse management practices.