Denise S. Rodriguez

Responses of Jatropha curcas to Salt and Drought Stresses

Two greenhouse experiments were conducted to quantify growth responses of Jatropha curcas to a range of salt and drought stresses. Typical symptoms of salinity stress such as leaf edge yellowing were observed in all elevated salinity treatments and the degree of the foliar salt damage increased with the salinity of irrigation water. Total dry weight (DW) of Jatropha plants was reduced by 30%, 30%, and 50%, respectively, when irrigated with saline solutions at electrical conductivity of 3.0, 6.0, and 9.0 dS m − 1 compared to that in the control. Leaf Na + concentration was much higher than that observed in most glycophytes. Leaf Cl − concentrations were also high. In the drought stress experiment, plants were irrigated daily with nutrient solution at 100%, 70%, 50%, or 30% daily water use (DWU). Deficit irrigation reduced plant growth and leaf development. The DW of leaves, roots, and total were reduced in the 70%, 50%, and 30% DWU compared to the 100% DWU control treatment. In summary, salinity stress and deficit irrigation significantly reduced the growth and leaf development of greenhouse-grown Jatropha plants.

Growth and Physiological Responses of Maize and Sorghum Genotypes to Salt Stress

The growth and physiological responses of four maize inbred lines (CUBA1, B73, B5C2, and BR1) and four sorghum hybrids (SS304, NK7829, Sordan 79, and KS585) to salinity were determined. Fifteen days after sowing, seedlings were irrigated with nutrient solution (control) at electrical conductivity (EC) of 1.5 dS m−1 or saline solution at EC of 8.0 dS m−1 (salt treatment) for 40 days. Dry weight of shoots in maize was reduced by 58%, 65%, 62%, and 69% in CUBA1, B73, B5C2, and BR1, respectively, while that of sorghum was reduced by 51%, 56%, 56%, and 76% in SS304, NK7829, Sordan79, and KS585, respectively, in the salt treatment compared to their respective control. Salinity stress reduced all or some of the gas exchange parameters, leaf transpiration (E), stomatal conductance (gs), and net photosynthetic rate (Pn) in the late part of the experiment for both crops. Salinity treatment greatly increased Na

Land Application of Treated Industrial Wastewater on a Chihuahuan Desert Shrubland: Implications for Water Quality and Mineral Deposition

Land application of wastewater conserves fresh water and recycles nutrients, but little is known of its impacts on arid and semiarid landscapes. Lagoon treated saline−sodic industrial effluent was applied from 2002–2005 to a 0.4-ha Chihuahuan Desert shrubland to assess the deposition and recovery of effluent components and changes in soil quality vis-à-vis a non-irrigated area. Effluent irrigation supplied 26% of the average annual nonstressed evapotranspiration (ET) of the native shrubs [Larrea tridentata (DC.) Coville and Prosopis glandulosa Torr. var. glandulosa], and increased both soil stress factors (sodicity, salinity, and pH) and soil fertility (N, P, and K). After 3 yr, the soil saturation extract electrical conductivity (ECe) reached as high as 6.1 dS m−1 and Cl− 76 molc m−3 at 105 cm depth under irrigated L. tridentata. After 4 yr, saturation extract sodium adsorption ratio (SARe) reached 25–35 at 7.5 cm under the irrigated shrubs and intershrub spaces. There were 27 Mg ha−1 of cumulative ionic deposits to the site comprised mostly of Na+, Cl−, and CaCO3 equivalent alkalinity, with soil analysis recovering most of the deposits (>57%) except for K+ and Na+ (8% to 13%). Subsurface leaching of and P was detected within the upper 1 m soil depth after 4 yr, and a high downward mobility of Cl− revealed the potential for deeper leaching at higher N loading rates. While long-term effects on the natural vegetation are unknown, results contribute to a limited scientific database for sustainable wastewater land application in semiarid regions.

Land Application of Treated Industrial Wastewater on a Chihuahuan Desert Shrubland: Impacts on the Natural Vegetation

Impacts of wastewater land application on desert vegetation are not adequately known. In a 4-yr field study, we evaluated the effects of treated, saline−sodic industrial effluent application on the aboveground vegetation biomass and mineral accumulation of a Chihuahuan Desert shrubland. The vegetation included two shrubs, Larrea tridentata (DC.) Coville and Prosopis glandulosa Torr. var. glandulosa, and seven herbaceous species in the intershrub spaces. Early summer fruit dry weights on terminal branches of the irrigated shrubs were 3 to 14 times higher than those on the non-irrigated shrubs. The combined irrigated vegetation produced 2 Mg of additional dried biomass per ha above that of the non-irrigated plot, and contained excesses of total Kjeldahl-N (TKN) and Ca2+ equivalent to 18% of effluent N deposition and 12% of effluent Ca2+ deposition. Under irrigated and highly sodic conditions (soil sodium adsorption ratio up to 35), the herbaceous Lepidium alyssoides A. Gray var. alyssoides produced the highest biomass of all plant species. However, there was a decline in plant species diversity as L. alyssoides became dominant in the irrigated intershrub spaces. While the findings demonstrate the natural attenuation of effluent minerals by native Chihuahuan Desert vegetation, highly sodic conditions may alter the composition of the vegetation community.