Mohamed A.M. Abdalla, Sobhy F. Mansour and Mona M.K. Abdel Razek( 2010). Effect Of Applying Gypsum On Some Physico-Chemical And Hydrological Properties Of A Saline-Sodic Clay Soil Provided With A Tile Drainage SystemFayoum J. Agric. Res. & Dev., Vol.24, No.2, July, 2010
Abstract: Ameliorating the saline-sodic soil process represents an important target in the agricultural security program of Egypt. In this concern, a field trial was conducted for improving a salt-affected clay soil provided with a tile drainage system at Mehallet Mousa, Kafr El-Shiekh Governorate, Egypt. The main target of this work was at identifying the effective role of applied gypsum, as a soil chemical amendment, with different rates on physico-chemical and hydrological properties of such soil as well as maximizing its productivity from maize and wheat crops. The applied gypsum treatments were categorized into: i. control without applied gypsum, ii. 3.75 ton gypsum/fed ≈ 75 % of gypsum requirements (GR) for the uppermost 15 cm, iii. 5 ton gypsum/fed ≈ 100 % GR and iv. 6.25 ton gypsum/fed ≈ 125 % GR. The applied gypsum rates were uniformly spread on surface and thoroughly mixed with the soil top 15 cm, and then followed by a recycle of wetting and drying was repeated four times through a period of about two months.. A recycle of wetting and drying was repeated four times through a period of about two months. Soil samples at depths of 0-15, 15-30, 30-45 and 45-60 cm were periodically collected after 3, 6, 9 and 12 months from starting the experiment to determine soil physico-chemical, i.e., ECe, ESP, salt leaching index, bulk density, infiltration rate, aggregation index and quickly drainable pores. Moreover, the shape of water table between drains, water table depth were monitored as well as the drainage intensity factor "a" and the rate of water drawdown were calculated.
The obtained results revealed that the reduction percentages of soil salinity after 3, 6, 9 and 12 months from starting the experiment reached 30.3, 33.1, 35.4 and 45.0 % for the applied gypsum rates 75 % GR vs 34.6, 36.9, 45.6 and 53.3 % for 100 % GR and 35.0, 66.6, 69.9 and 75.7 % for 125 % GR, respectively. That was true, since additional gypsum in excess of the requirement helped speedily soil amelioration process. In general, the soil salinity reached the safe limits of soil salinity (ECe=< 4.0 dS/m) and sodicity (ESP= < 15 %) after 6 months of applying 100 and 125 % GR. Also, the values of ECe and ESP were tended to a gradual decrease with increasing the experimental time, but the reverse was true for the values of salt leaching index that showed gradual increases. Concerning soil physical soil properties, the obtained results showed a pronounced increase in infiltration rate, where the increase percentages ranged 42.3-56.0, 43.7-60.9 and 55.4-91.5 % at 75, 100 and 125 % GR, respectively. A similar and parallel trend was also observed for the values of quickly drainable pores. Such favourable effect refers to the released Ca2+ from gypsum that leading to improve soil structure, creation of friable granules and conductive pores that enhancing water penetration, and then promote a sufficient cycle of wetting and drying. Also, a parallel increase was achieved for the aggregation index values as time elapsed and increasing gypsum rates, where the corresponding relative increase percentages ranged between 18.0-89.3, 55.0-120.0 and 108.0-140.3 % at 75, 100 and 125 % GR, respectively. Moreover, a noticeable decrease was observed for soil bulk density due to adding gypsum as an amendment comparing with the control treatment. Regarding soil hydrological properties, it was clearly showed a marked drop in water table level differs from one day to another as well as the applied gypsum rates, probably due to the nature of the stratified layering of such Nile alluvial soil. The average rate of water table drawdown after one year of gypsum application mounted 35.2, 44.8 and 95.0 % for soils treated with 75 %, 100 % and 125 % GR as compared with the initial state, respectively. In general, lowering the water table has given the top soil a chance to dry, shrink and creating water passageways. It was also noticed that the drainage intensity factor (a) tended to increase with increasing the applied gypsum rate, where its greatest value was achieved at 125 % GR, may be due to the increase of released Ca2+ and its positive action to link clay particles, and in turn enhance soil internal drainage and water movement to drains. In addition, a parallel pronounced decrease in the total water resistance was associated with increasing the applied gypsum rate, i.e., 7.69, 23.07 and 30.77 % at 75, 100 and 125 % GR, respectively. This means that applied gypsum led to improve the soil structure which helped in creating a more permeable soil medium with less resistance to water flow towards tile drains.The achieved amelioration in physico-chemical and hydrological properties of the studied soil positively reflected on the increases of grain yields of both summer maize and winter wheat, which were approached 27.8, 50.0 and 61.1 % for maize vs 25.7, 42.9 and 57.1 % over the control for wheat at 75, 100 and 125 % GR, respectively. Finally, the obtained results suggest that this work is considered as scientific and logic fundamental base for a successful agricultural development of such salt affected area as well as possible to increase unite area income.
Keywords: (Saline-sodic clayey soil, gypsum, tile drainage system, soil amelioration. )
