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THE POSSIBLE USE OF HUMIC ACID INCORPORATED WITH DRIP IRRIGATION SYSTEM TO ALLEVIATE THE HARMFUL EFFECTS OF SALINE WATER ON TOMATO PLANTS

The main purpose of this work was to evaluate the possible use of humic acid mixed with the irrigation water through a drip irrigation system to alleviate the harmful effects of salinity stress on growth, fruit yield and quality of tomato plants (Lycopersicon esculentum, c.v. 1077 hybrid). To achieve this target a field experiment was carried out on a private farms at Sedmant El Gabal village, Beni-Suef Governorate, Egypt, which represents one of the those are occupying the desert zone adjacent to the western edge of the Nile Valley during two successive seasons of 2005-2006 and 2006-2007. Two irrigation water resources were used, i.e., the Nile water (C1S1, ECiw = 0.56 dS/m and SAR = 2.13) and a mixture of agricultural drainage saline water with the Nile water at a ratio of about 1:1 (C2S1, ECiw = 1.89 dS/m and SAR = 5.35). Humic acid was applied at rates of 75, 150 and 225 mg/L through a drip irrigation system twice/week and for a period of 4 months after transplanting. The obtained data reveal that the studied soil is mainly encompassing the wind blown sand deposits as a parent material, and it is classified as Typic Torripsamments, siliceous, hyperthermic and it could be evaluated as marginally suitable. The results also show that usage of saline water resulted in relative increases of the ECe and ESP values in the root zone reached 18.95 and 33.09 % as compared to the initial state of soil, respectively. Meanwhile, the corresponding relative increases of the ECe in case of amended saline irrigation water with humic acid at rates 0. 75, 150 and 225 mg/L were 11.75, 5.09 and 2.98 %, vs 10.84, 3.76 and 1.73 % for the ESP values, respectively, with its optimal case at a rate of 225 mg/L. Moreover, the applied humic acids played an important role in improving the values of soil bulk density, total porosity, available water and hydraulic conductivity, organic matter content, pH, CEC and available nutrients. The latter may be due to modified airmoisture regime that leads to alleviate the depressive effect of salinity stress on the released nutrient from organic residues. These favourable conditions of the improved soil due to amended irrigation water positively reflected on the vegetative growth and flowering parameters of tomato plants, i.e., plant height, number of leaves/plant, thickness of stem/plant at soil surface, number of branches/plant, leaf area, number of inflorescences/plant, number of flowers/inflorescence, dry weight/plant, and the chlorophyll a & b contents. It is evidently that such beneficial effect of humic acid on the dry matter productions was more attributed to the leaves area and number, which are contributed to more photosynthesis and better carbohydrates yield. Also, the ability of humic acid for increasing plant nutrient uptake is due to its chelating property. Moreover, the applied humic acid at all the different rates resulted in significant increases for N, P and K in tomato leaves. The reverse was true for Na and Cl, probably due to alleviate the harmful effect of saline irrigation water. In addition, using humic acid at the rates of 150 and 225 mg/L mixed with saline irrigation water Ashraf Sh. Osman & Mohamed S.A. Ewees Fayoum J. Agric. Res. & Dev., Vol.22, No.1, January, 2008 53 registered almost similar tomato yields to those irrigated with the Nile water and higher than those irrigated with either saline water or treated with at a rate of 75 mg/L humic acid. The relative increases in fruit yield/plant or fed could be attributed to significantly higher increments in dry weights and number of flowers/plant. The parameters of tomato fruit quality, i.e. average weight of fruit, fruit firmness, total soluble solids (TSS), vitamin C (ascorbic acid), titrable acidity (citric acid) and total sugar showed significantly increased when treated with amended saline irrigation water with humic acid at the applied rates as compared to the effect of used saline water solely. Thus, the present study shows that the best rate of the applied humic acid mixed with the used irrigation saline water was 150-225 mg/L for achieving the greatest tomato yield of high quality.