Influence of Organic Wastes on Evaporation and Hydraulic Properties of Sandy Soil
Ahmed Farid Saad
A laboratory experiments were conducted to examine the influence of various organic wastes on evaporation and some of hydro-physical properties of sandy soil collected from Al-Bustan region, Egypt. Five treatments: control, 1% of wheat straw, % clover straw, mixture of wheat & clover, and chicken manure on the basis of air dry weight of sandy soil (0.529 kg/m2) were applied directly on soil surface. The same treatments were done with incorporation of organic wastes. Also, plastic mulch used in the two cases of applications as a tool for maximizing the role of organic wastes for reducing evaporation from surface layer of sandy soil. Soil samples were subjected to wet and dry cycles (1st experiment). In 2nd experiment was conducted to evaluate the role of organic wastes for improving the hydraulic properties of sandy soil. The average values of evaporation reduction percentages in case of addition organic wastes on surface of sandy soil, were 22%, 10.4%, 9.8% and 40%, 21.7%, 16.6% in chicken manure and clover straw(CS) treatments along wet and dry cycles in the first, second and third runs (2, 4 and 6 days intervals), respectively. The average values of evaporation reduction percentages, in case of incorporation organic wastes with sandy soil, were 21.3% and 31.7% in chicken manure and mixture of wheat and clover straw (WS+CS) treatments in the first run (2days intervals), respectively while it were (4.9%, 12.4%) and (1.1%, 5.4%) in chicken manure and (WS+CS) treatments in the second and third runs (4 and 6 days intervals), respectively. Using plastic mulch with surface application of organic wastes treatments (SAOWT) on sandy soil reduced the average daily evaporation rate by 21.54% to 35.97% while it reduced by1% to 15.6% in incorporated organic wastes treatments (IOWT) compared to control treatment. Linear equations with high R2 are given to describe and quantify the relationship between evaporation rate and time in all cases of using plastic mulch. Organic wastes led to decrease the values of hydraulic conductivity in sandy soil. Determined values showed that Ks decreased to 51%, 33% and 16.5%, respectively in WS+CS, CS and WS treatments compared to control. Ks (t) for all treatments were fitted to 2nd order polynomial equation with high R2. Basic infiltration rate values decreased substantially by about 33% in incorporated broad bean straw and chicken manure while it were decreased by about 78% and 50% in case of wheat and clover straw compared to control treatment, respectively. There was a lag time in wet front advance between organic wastes treatments and control treatment. The lag time was ranged between 20 and 7 minutes for clover straw and wheat straw treatments, respectively. Distribution of water content with depth of soil columns appeared the polynomial trend with high values of R2. Incorporated sandy soil columns with clover straw and chicken manure increased the percentage of water holding capacity 20.1 and 15.2%, respectively compared to control treatment. There were highly significant differences between most of treatments.
Key words: Organic wastes, plastic mulch, Evaporation, Infiltration rate, wet front advance, water content, hydraulic conductivity.