Saturday, 15 July 2006

Plant Response to Salinity in Gypsum-Saturated Solutions.

Juan Felipe Martinez-Montoya and Victor M. Ruiz-Vera. Colegio de Postgraduados, Iturbide 73, Salinas, Mexico

There are at least 1,000,000 hectares of gypsiferous soils in the arid lands of Mexico. The agricultural productivity of these soils is low because of their low nutrient content, poor moisture retention, and low cation exchange capacity. Moreover, the lack of information regarding the plant response to salinity under a gypsum saturated soil solution has caused an indiscriminate use of fertilizers (which not necessarily has increased the crop yields) leading to land degradation. This research is conducted to evaluate the plant response to gypsum-saturated solutions with increasing concentrations of NaCl or MgSO4 (electrical conductivity basis [EC = 0 to 30 dS m-1]). Fifteen cultivars (including three gypsophile species) were evaluated. Germination rate and final germination percentage were determined using a germination chamber at alternate temperatures of 21-23 C. A hydroponics system in a greenhouse was used to evaluate growth rate, dry matter production, and crop yield. Preliminary results showed that the germination process depended on the plant species, the salt type and its concentration, and the presence or not of gypsum-saturation condition. The germination percentage and the germination rate decreased with increase in salinity. The germination rate was more sensitive than the final germination percentage to increasing values of NaCl and MgSO4 salts either in gypsum-saturated conditions or with no presence of gypsum. Thus, the final germination percentage was not affected significantly for corn (Zea mays L.) and black bean (Phaseolus vulgaris L., var. T-39) at any EC value, with exception of EC = 30 dS m-1. The percentage of germination decreased 13% for MgSO4 or MgSO4 + gypsum (EC = 30 dS m-1) with respect to the control (distilled water, 0.007 dS m-1), and decreased 17% for NaCl and 37% for NaCl + gypsum. The reduction in the germination rate attributed to salinity was more evident in tomato (Lycopersicon esculentum Mill.), onion (Allium cepa L.), and corn. An electrical conductivity of 30 dS m-1 completely inhibited the germination of tomato seeds. Regarding the comparison between salt types, NaCl caused a larger reduction in the percentage of germination for all the species compared with MgSO4. The highest NaCl salinity produced an effect on the germination rate of alfalfa (Medicago sativa L.) seeds only after 5 days of treatment whereas the rest of salt levels had similar values of germination. Thus, MgSO4 produced higher germination percentage of alfalfa seeds than NaCl. For onion, the highest salinity (30 dS m-1) delayed three days the germination onset and the germination percentage decreased 60% compared with the control. On the other hand, the decrease in the percentage of germination with increasing salinity was steeper with gypsum-saturated solution compared with solutions without gypsum addition. An exception to this behavior was observed in onion and tomato for high EC values. Thus, at low values of NaCl salinity (EC £ 10 dS m-1) the presence of gypsum had no effect, or caused a decrease in the percentage of germination and the germination rate of tomato seeds. On the other hand, when the EC was 18 or 30 dS m-1, the presence of gypsum-saturated solution improved the germination of alfalfa seeds compared with non-gypsum treatments. The same response was observed for tomato at 18 dS m-1 with NaCl and MgSO4 salts.

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