Submitted to: Agricultural Water Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/11/2004
Publication Date: 11/20/2004
Citation: Grieve, C.M., Poss, J.A., Grattan, S.R., Suarez, D.L., Benes, S.E., Robinson, P.H. 2004. Evaluation of salt-tolerant forages for sequential reuse systems. II. Plant-ion relations. Agricultural Water Management. 70:121-135. Interpretive Summary: The westside of the San Joaquin Valley of California has very few natural outlets for drainage of agricultural wastewaters. As a result, strategies have been proposed to reuse of these waters for irrigation of selected crops. The suitability of the waters for crop production will depend on the hazards they pose to sustained crop production. Salt tolerant forages may play an important role in drainage water reuse management provided the unique ion composition of the effluents does not adversely affect the balance of essential plant mineral nutrients which may result in symptoms of ion toxicities or deficiencies, e. g. leaf burn, yellowing, or death. In this study we grew ten forages in greenhouse sand cultures irrigated with waters prepared to simulate drainage waters of moderate and high salinity. Crops were two cultivars of alfalfa, two trefoil species, tall wheatgrass, alkali sacaton, two cultivars of paspalum, kikuyugrass, and bermudagrass. With the exception of broadleaf trefoil which struggled at moderate salinity and died at high salinity, none of the forages showed visible signs of ion toxicity or deficiency. During this year-long trial, patterns of shoot ion concentrations were unique for each crop and varied with salinity level, harvest date and plant age. For example, magnesium in alfalfa grown at moderate salinity barely met the level required for proper nutrition. On the other hand, high concentrations of sulfate in the irrigation waters resulted in levels of sulfur in all the forages which were three times more than the plants require. Several of the forages were able to limit the amount of sodium taken up into the shoot, despite the high concentrations of sodium present in the irrigation waters. The value of these forages to ruminant nutrition depends on ion concentrations, balances and interactions in the herbage. This topic is discussed in the companion paper: Evaluation of salt-tolerant forages for sequential reuse systems. Part III. Implications for ruminant mineral nutrition.
Technical Abstract: Implementation of the saline drainage water reuse system proposed for the westside of the San Joaquin Valley (SJV) of California requires development of sustainable cropping systems which incorporate useful, salt tolerant agronomic species. Ion composition in the saline drainage effluents present in the SJV is unique, with Na+, SO42-, Cl-, Mg2+ and Ca2+ predominating in that order. To identify potentially suitable crops for reuse systems, ten forages were tested in greenhouse sand cultures located at USDA-ARS George E. Brown Jr. Salinity Laboratory, Riverside, California. Crops were: alfalfa (Medicago sativa L.) cvs. 'Salado' and 'SW 9720'; narrowleaf trefoil (Lotus glaber Greene) cv. 'PI 608022'; broadleaf trefoil L. ulginosus Schk.) cv. 'Big'; tall wheatgrass (Agropyron elongatum (Host) Beauv.) cv. 'Jose'; alkali sacaton (Sporobolus airoides Torr.); kikuyugrass (Pennisetum clandestinum Hochst. Ex Chiov.) cv. 'Whittet'; paspalum (Paspalum vaginatum Swartz) cvs. PI 299042 and 'Polo'; and bermudagrass (Cynodon dactylon (L.) Pers.) cv. 'Tifton'. Two saline treatments, 15 and 25 dS/m, were imposed. Shoots were subsampled for mineral ion analysis when the forages were harvested. Patterns of shoot ion concentrations were unique for each species and varied with salinity level, external ion ratios, harvest date and plant age. Plant preference for K+ over Na+ did not appear to be a reliable predictor of salt tolerance. Salt tolerant crops, such as kikuyugrass and bermudagrass, were highly selective for K+ (SK, Na ~200 to 400), whereas selectivity coefficients for the equally salt tolerant grasses, alkali sacaton and tall wheatgrass, ranged from 20 to 40. The forages were highly selective for K+ over Mg2+ despite unusually low K+:Mg2+ ratios in the external solutions. Total-S in the herbage was high, and generally increased as external SO4-2 increased. Based on sustained nutritional health and lack of visual signs of toxicity or deficiency symptoms, several of the forages tested show promise as suitable candidates for the saline-sodic water reuse systems.