The role of humic substances in mitigating the harmful effects of soil salinity and improve plant productivity

The environmental, social and economical reasons indicate that the conventional agriculture constitute a continuous pressure contributing to the progressive worsening of environmental conditions, especially by an increasing apply high level of inputs. In this matter, the increasing use of saline irrigation water is one of the main factors resulting in salt accumulation in the plant rhizosphere influencing both physical, chemical and biological soil properties and agroecosystem productivity. In this situation, soil degradation emphasized the need to develop strategies of salt effected soil reclamation. One of the possible solutions is to use humic substances (HS), since there is an increasing need to their utilization in agriculture. They are the major components of soil organic matter, have multiple roles in plant growth and are the subject of study in various areas of agriculture, such as soil chemistry, soil fertility and plant physiology. Thus, our hypothesis account for a beneficial effect of HS in salt affected rhizosphere likely due to a 'direct' action on the plant together with an 'indirect action' on the metabolism of soil microorganisms, the dynamics of uptake of soil nutrients and soil physical conditions. In this paper we review the HS formation and components and their influences on improving saline soil properties as both direct and indirect effects. Keywords: Humic substance; Salt accumulation; Soil degradation; Plant productivity; Hormone-like activity.