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Title: EVALUATION OF SALT-TOLERANT FORAGES FOR SEQUENTIAL WATER REUSE SYSTEMS. I. BIOMASS PRODUCTION

Author
item GRATTAN, STEPHEN - DEP LAWR, UC DAVIS,CA
item Grieve, Catherine
item Poss, James
item ROBINSON, PETER - DEP ANIM SCI, UC DAVIS
item Suarez, Donald
item BENES, SHARON - D PLANT SCI, CA ST FRESNO

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2004
Publication Date: 11/10/2004
Citation: Grattan, S.R., Grieve, C.M., Poss, J.A., Robinson, P.H., Suarez, D.L., Benes, S.E. 2004. Evaluation of salt-tolerant forages for sequential water reuse systems. I. Biomass production. Agricultural Water Management. 70:109-120.

Interpretive Summary: In semiarid regions with irrigated agriculture, such as the San Joaquin Valley (SJV) of California, drainage of the farmland is necessary for sustaining long term productivity. Drainage effluents in the Valley contain dissolved salts and other constituents such the potentially toxic trace elements, selenium (Se) and molybdenum (Mo). Unfortunately, the Valley has very few drainage outlets to manage the disposal of these waters. One of the few on-farm options available to growers in the Valley is the reuse of drainage waters for irrigation, a management practice which would reduce the volumes of drainage water requiring disposal and increase productivity of these lands. Another problem that exists in the SJV is the shortage of high quality forages for dairy and beef cattle. Salt-tolerant forage crops that could grow well under salinity irrigation would not only increase forage supplies but could play a key role in drainage water management. Our objective of this year-long experiment was to identify suitable, high-quality forage species for the reuse system. We grew ten forage crops in greenhouse sand cultures irrigated with typical SJV waters at two levels of salinity (moderate and high) each containing low concentrations of Se and Mo. The forages were: alfalfa (cultivars 'Salado' and 'SW 9720', tall wheatgrass ('Jose'), narrowleaf and broadleaf trefoil, paspalum (cultivars 'Polo" and PI299042, alkali sacaton, kikuyugrass, and bermudagrass. Based on dry matter production at moderate salinity, we found that alfalfa and paspalum 'PI299042' were the best producers. At higher salinity, however, the more salt sensitive alfalfa was out-produced by the top candidates: paspalum 'PI 299042', tall wheatgrass and bermudagrass. Most of the forages tested could easily fill a niche in a drainage water reuse system. This paper (I. Biomass production) is one of three reports on the plant-animal system existing in the SJV where saline drainage effluents are used for irrigation. The second (II. Plant ion relations) addresses the effect of ion concentrations the irrigation waters on forage nutrition and ion uptake. The third (III. Implications for ruminant mineral nutrition) reports on the contribution of forage mineral ion content and interactions which affect cattle and sheep.

Technical Abstract: Reuse of saline drainage waters is a management option that has been suggested for the San Joaquin Valley (SJV) of California in order to reduce both the area affected by shallow water tables and the volume of drainage effluent requiring disposal. Salt-tolerant forages may play an important role in this strategy, while at the same time producing a food source for sheep and dairy cattle. Crop selection for reuse systems, however, will depend upon production potential under saline-sodic conditions. To identify potentially suitable crops, a controlled study using an elaborate sand-tank system was conducted at the US Salinity Laboratory to evaluate ten promising forage crops irrigated with synthetic drainage waters dominated by sodium sulfate with an EC of either 15 or 25 dS/m each containing 500 micrograms/L Se and Mo as selanate and molybdate. Forages were cut several times over the year-long duration of the experiment. The forage species tested performed differently in terms of absolute biomass accumulation and biomass production relative to salinity level. Cumulative biomass production of alfalfa (Medicago sativa L.), a relatively salt sensitive crop, was higher than most other forages at moderate salinity. As salinity increased to 25 dS/m, however, cumulative biomass of the alfalfa cultivars were reduced by nearly half whereas biomass of the more salt tolerant grasses was only reduced by about 15% to 25%. Although most forage species tested showed promise, those that performed particularly well based on biomass accumulation, overall salt-tolerance, and forage quality were 'Jose' tall wheatgrass, bermudagrass and 'PI 299042' paspalum.