Influence of salinity and water content on soil microorganisms

Salinization is one of the most serious land degradation problems facing world.Salinity results in poor plant growth and low soil microbial activity due to osmotic stress and toxic ions.Soil microorganisms play a pivotal role in soils through mineralization of organic matter into plant available nutrients.Therefore it is important to maintain high microbial activity in soils.Salinity tolerant soil microbes counteract osmotic stress by synthesizing osmolytes which allows them to maintain their cell turgor and metabolism.Osmotic potential is a function of the salt concentration in the soil solution and therefore affected by both salinity(measured as electrical conductivity at a certain water content)and soil water content.Soil salinity and water content vary in time and space.Understanding the effect of changes in salinity and water content on soil microorganisms is important for crop production,sustainable land use and rehabilitation of saline soils.In this review,the effects of soil salinity and water content on microbes are discussed to guide future research into management of saline soils.

Has“Grain for Green”threaten food security on the Loess Plateau of China?

There is debating over the question of whether the large-scale‘Grain for Green’program on the Loess Plateau of China threatens regional food security.Self-sufficiency index and cropland pressure index were used to assess food security on the Loess Plateau after the implementation of revegetation program.The results showed that the‘Grain for Green’program initially had a considerable impact on regional food security,where grain yield fell from 1999 to 2001,resulting in a lower grain self-sufficiency and increased farmland stress.Subsequently,grain yield in this region increased due to the elevated agricultural material input and increased construction of terraces and check dams.The grain self-sufficiency index would have increased to 96.55%if there were improvements to the agricultural conditions,such as fertilization and irrigation,which would have resulted in an increase in the crop yield per unit of 20%.However,the grain self-sufficiency increased to 105.25%via the construction of terraces and check dams.Thus,the government should further expand the‘Grain for Green’program in coordination with improvements to the agricultural production conditions and the construction of terraces and check dams on the Loess Plateau.