Laboratory evaluation the effect of some organic amendments as a remediation strategy for a saline-sodic soil

Reducing the capacity of preservation of water and nutrients, poor soil aggregation, instability of soil structure, reducing the rate of water infiltration into the soil, reducing microbial activity, reducing soil fertility and consequently reducing growth and yield of plants are the common problems of saline-sodic soils. Among of the agricultural soil amendment which can enhance agricultural productivity and soil sustainability, one that is organic in nature, is biochar. Biochar is the product of pyrolysis of many types of organic materials in the absence or partial absence of oxygen and at high temperature (usually around 450 degrees Celsius). More recent studies have reported positive improvements from the incorporation of biochar into poor soils, including decreased bulk density, increased water holding capacity, liming effect, and enhanced nutrient availability; but it depends on the type of feedstock’s and production conditions of the biochars. Due to the fact that in our country, the area of saline-sodic soils is very large (10-15% of the country's area) and a little research has been done about the effect of usage of various types of organic modifiers on the improvement of saline-sodic soils properties, consequently, this study aimed to investigate the effects of adding some of organic modifiers, which most of them were organic wastes, on some physical and chemical properties and to improve saline-sodic soil.

This study was carried out in a saline-sodic soil as a pot experiment in a completely randomized design with 13 treatments and 3 replications in the greenhouse conditions at the University of Jiroft. Treatments including 6 types of organic modifiers (wheat straw, palm waste, vermicompost, cocopeat, wheat straw biochar and palm wastes biochar) that each one was considered at two levels (5 and 10%) with control. The organic modifiers were later grounded and sieved with 2 mm sieve and made ready for application. The treatments were added to saline-sodic soil and incubated for 90 days by maintaining moisture content at the moisture of the field capacity of soil (it was done by weighing the pots). After incubation period, some chemical and physical properties of soil including pH, salinity (EC), sodium adsorption ratio (SAR), bulk density and clay dispersion were measured. Also, some biological properties including soil microbial respiration and alkaline phosphatase activity were measured.  Data collected from each experiment were subjected to analysis using SAS Ver.9.4. The differences between mean values were identified using Duncan’s multiple range tests at a significance of p< 0.01.

The results indicated that adding organic modifiers caused significant changes in physical, chemical and biological soil properties.  Addition of organic modifiers to the soil caused a significant decrease in pH and SAR compared to control pots. All organic modifiers greatly increased soil microbial respiration, alkaline phosphatase activity and EC in compared to the control and organic modifiers addition at a higher level finally resulted in a higher value of soil EC. Application of organic modifiers soil reduced clay dispersion of the soil compared with the control. For example, clay dispersion was significantly reduced about 52 and 54 percent in compared to the control, by adding 10% of wheat straw and palm waste, respectively. Other organic modifiers had less effect on reducing clay dispersion than wheat straw and palm waste, but effect of all treatments on this parameter were significant in compared to the control. Also, the results of this study showed that addition of all organic modifiers to the soil, decreased soil bulk density compared to control which maximum decreasing was observed by application 10% of cocopeat and wheat straw biochar. Biochar has high porosity which results from retaining the cell wall structure of the biomass feedstock. Therefore, being a porous material when added to the soil, it increases its porosity and thus reduced bulk density.

According to the results, cocopeat particularly at 10% level application, had highest effect on soil properties and to improve of saline - sodic soils. Generally, the use of organic materials in poor soils could increase the soil organic matter therefore improves its physical and chemical properties of soil, especially when the soil has additional problems from destructive factors such as salinity and sodicity. In addition, organic modifiers production has caused the optimal use of agricultural and industrial wastes and can be used to protect the environment and reduce pollutants. Also, the use of these wastes as biochar could be a more environmentally friendly solution. However, further researches are needed to determine the impacts of a specific biochar on a specific saline- sodic soil.