Salinization and its Impacts on the Environment: Soil salinization is a historical problem affecting agriculture sector all over the world in areas lying under arid and semi-arid climates including Pakistan. It is a continuous problem and has an equilibrium with normal soils.
Temperature, availability of fresh water, underground water quality, cropping patterns and management practices are significant factors affecting this equilibrium. In Pakistan, out of 79.6 million hectares of total area, about 9.97 million hectare is salt affected which is about 42 percent of the total cultivable area. Salt-affected soils may be categorized in to three main categories including saline, saline-sodic and sodic, but the dominated one are saline-sodic soils which have higher concentration of total soluble salts as well as the excess of sodium. The salt equilibrium gets disturbed when intake of salts is higher than the harvest in the form of leaching or crop removal.
Such excessive concentrations of salts affect the physical, chemical and biological characteristics of soils. Deterioration of soil characteristics impede the plant growth causing specific ion toxicity, osmotic deregulation, an increase in soil pH and nutrients imbalance. These limiting factors drastically decrease the crop yields and chalk out a big question mark on food security. Besides the deterioration of cultivable soils due to salinization, the industrialization and overpopulation are also shrinking the volume of agriculture soils. Under these circumstances, the only viable option is to bring the salt-affected soils under cultivation because the discovery of new lands for cultivation is not possible.
Biochar as an Effective Amendment
Adaptation of reclamation and sustainable management practices is the only workable option that can assist to increase the land for agricultural crops. There are different amendments which are being used to minimize the effects of salinization. Biochar, a pyrolysis product of organic matter under limited supply of oxygen is the most suitable amendment that is of considerable interest and gaining importance for improvement of salt affected soils. It is a carbon enriched material and produced by anaerobic burning of organic matter at a temperature ranging from 300 to 1000 °C.
Different biochar’s have different impacts on the salt affected soils depending on the conditions under which pyrolysis is done. It has the ability to enhance the soil physicochemical properties as well as plant growth by maintaining the bioavailability of mineral nutrients. It has large surface area, high cation exchange capacity, active functional groups, and micro porous structures. All these characteristics make it a good agent for the adsorption of excessive salts, offers high water and nutrient holding capacity, and improvement in soil structure.
Remediation Ability of Biochar for Salt-Affected Soils
Biochar application in soil increases plant growth, biomass, and nutrient uptake under water and salt stress conditions. As biochar is sourced from organic material, it carries a pool of nutrients (e.g K, Ca, Zn, Mg, Mn) which have varying release rates. Hence, it improves the fertility status of salt affected soils and nutrient availability to plants growing in such soils. It reduces sodium ion (Na+) toxicity to plants and increase potassium (K+) uptake under salt stress. Moreover, it is also source of calcium ions and replace sodium from exchange sites of soil by providing calcium in soil solution.
Biochar also has the ability to hasten the excessive salts leaching and thus decrease the leaching time of salts to a level that is highly suitable for crops. Its organic carbon contents increase the soil aggregate stability for a longer period of time than short term degradable molecules of simple organic amendments. Being a habitat for a number of soil microorganisms, it helps in improving salt-affected soils.
But all of these effects of biochar primarily depends on three factors including nature of feedstock, pyrolysis conditions, and rate of biochar added. Characteristics of biochar changes greatly with change in any of these factors. When it is produced with slow pyrolysis at high temperature having lignocellulosic feedstock is more stable as compared to quick pyrolysis and non-woody feedstocks. However, when it is produced from the non-woody feedstocks like plant residues and organic manures, it has higher pH, much richer in nutrients, and contain less stable carbon.
Economic Benefits of Biochar Over other Organic Amendments:
Organic amendments like compost and manures also have the ability to reclaim the salt affected soils. It is worth mentioning that they have characteristics similar to biochar and play an important role in enhancing the soil properties and plant growth. Nevertheless, biochar is more effective and acceptable regarding its stability in soil, application rate, and environment friendly nature. Simple organic materials need to apply at regular intervals and at higher rates in arid and semi-arid regions where high temperature increases their decomposition rate.
Hence, excessive application of quickly decomposable organic matter leads to higher emission of greenhouse gases (CO2) and require more economic costs. Moreover, if these amendments have higher contents of NH4, K and Na, they may increase the salinization upon decomposition. So, application of biochar is a better option because it is much more stable (decade to centuries), feasible economically, and have higher environmental significance’s.
Biochar proves to be extremely proficient and a sustainable approach to use in lands degraded by salts where it can support cultivation. Also, it plays an important role in increasing soil fertility and carbon sequestration, therefore, salinization and its associated hazards can be avoided through its application. Moreover, it is economical, productive and efficient for rehabilitation of salt affected soils.
Thus, in order to cope with salinity and sodicity, it is a supportive recommendation to focus on biochar use along with other management practices in agriculture. Through its use, we can improve overall productivity of our salt affected soils, earn income, and reduce poverty by getting benefits from cultivation of these soils.
This article is collectively authored by Aisha A Waris, Muhammad Zia-ur-Rehman, and Muhammad Umair