In a world where global temperatures are rising to unprecedented levels, millions of species face extinction, and hundreds of millions of people are faced with the possibility of losing their homes, salty soils are probably the furthest thing from your mind. However, soil salinization poses a major threat to global food security and has consequence that are already effecting large portions of the population. As climate change causes temperatures to increase around the world, our dependence on irrigation to maintain our agricultural productivity increases along with it. The constant irrigation of soils causes them to erode and salt to build up in the soils over time. Once these soils become salt-affected, they can no longer support plant growth and may ultimately need to be removed in order to restore the land’s productivity. This issue is estimated to affect over 240,000 square miles, an area roughly the size of Texas, and cost our global economy 27.3 billion dollars, which is almost six times Germany’s GDP. Because soil salinization is such a widespread issue, scientists are currently exploring crop management and breeding techniques that will allow us to continue to feed our growing populations.
Plants aren’t able to grow in salt-affected soils for the same reason that humans can’t quench their thirst with a glass of saltwater. Exposing plants to high concentrations of salt dehydrates their cells and makes it much more difficult for them to perform the regular maintenance that keeps them alive. Plants typically use 60-90% of their energy to perform this maintenance, so when they are placed under stress from environmental factors, it becomes much more difficult for them to grow (Munns). This is the reason that soil salinity is commonly associated with loss of crop yields and stunted plant growth.
To assess just how much of these staple crops were being lost to soil salinization, a study was conducted in 2016 by Dr. Onur Satir on the Lower Seyhan Plain of Turkey. This area was selected due to its ideal farming conditions, other than infiltration of salts from coastal waters. Based on assessments from satellite imaging and geographical information software, researchers found that under moderate salinity conditions, cash crops yield losses were averaging over 30%. This includes a 15% loss for cotton, a 28% loss for wheat, and a striking 55% loss for corn. Losses like these are not isolated to this region. According to the UN sustainable development journal, major arid and semiarid regions like the Yellow River Basin in China, the Indo-Gangetic Basin in India, and the Murray-Darling Basin in Australia are experiencing similar effects.
Due to its climate, South India is a region that is especially prone to soil salinization. Unlike Turkey, whose climate and soil conditions are otherwise optimal for farming, South India is subject to seasonal weather events that make the area especially prone to salt buildup in soils. The country’s long monsoon season weathers the soil bedrock and leaves behind large salt deposits when the water is evaporated. The country also experiences a dry season for the rest of the year that requires the use of heavy irrigation to grow crops, which further weathers soil bedrock and brings eroded salts to the soil surface. If that wasn’t enough, this region’s proximity to the coast also makes it prone to flooding events that cause salt from the ocean to invade the water supply. A study conducted in 2003 by G. Swarajyalakshmi found that salt-affected soils were yielding losses of over 50% for many of the region’s crops, including rice, wheat, and cotton. Not all plants in the region experienced such dramatic losses. More salt tolerant crops like safflower and mustard were virtually unaffected by the area’s saline conditions.
There are many crops, in fact, that are able to grow successfully in saline environments. These plants are known as halophytes and have special adaptations that allow them to either avoid taking in salt ions from the soil, or successfully avoid dehydration in their cells when these ions are present. According to Dr. Rana Munns, many of these halophytes are crops that have had the evolutionary advantage of being considered somewhat unappealing to humans. By avoiding the heavy selective breeding that many cash crops are subject to, these plants have maintained greater genetic diversity and improved abilities to adapt to their environments. Dr. Munns suggests that this is the reason that many strains of barley that grow in rural areas like Central Asia are able to maintain higher crop yields under saline conditions than those that have been heavily domesticated. She also points to selectively breeding for adaptations that allow these plants to grow successfully in salt-affected environments as a solution to the global food security issue that is being created by this phenomenon.
Dr. Munns is not the only scientist that has begun to explore solutions to the increasing problem of soil salinity. Many researchers are investigating what new kinds of crops and management strategies will allow us to continue feeding our growing populations as this issue progresses. One study conducted by Dr. Jianxia Sun in China investigated the effects of implementing drip irrigation on reducing the salinity of soils. The study found that this management strategy was able to reduce the salinity of soils by almost 65%. This reduction in salinity made it possible for all plants that were moderately salt tolerant to grow and those almost 50% of all plants to grow successfully after 4 years of treatment. While this victory may appear small compared to the large scope of this issue, it gives us hope for the possibility of implementing sustainable management solutions in the future.
Managing soil salinization will continue to pose a challenge to regions that are affected by this phenomenon. While wealthier nations like Australia and the US have already committed billions to implementing management programs, many of these affected regions fall within developing nations with governments that lack the capital to do so. For countries like India, outside funding will be necessary to implement solutions that will allow their soils to continue supporting their growing population. Despite the challenges that come with managing soil salinization, it is urgent that affected regions take action to mediate its effects. The UN estimates that a plan of no action could cost countries millions of dollars and a loss of up to 60% of their crop yields. With estimates of nearly 10 billion mouths to feed by 2050, funding programs and research to combat this threat could not be more urgent.
by: A. Houck
References
Jiaxia Sun, Yaohu Kang, Shuqin Wan, Wei Hu, Shufang Jiang, Tibin Zhang, Soil salinity management with drip irrigation and its effects on soil hydraulic properties in north China coastal saline soils, Agricultural Water Management, Volume 115, 2012, Pages 10-19, ISSN 0378-3774, doi: 10.1016/j.agwat.2012.08.006.
Munns, R. and Gilliham, M. (2015), Salinity tolerance of crops – what is the cost?. New Phytol, 208: 668–673. doi:10.1111/nph.13519
Onur Satir, Suha Berberoglu, Crop yield prediction under soil salinity using satellite derived vegetation indices, Field Crops Research, Volume 192, 2016, Pages 134-143, ISSN 0378-4290, doi: 10.1016/j.fcr.2016.04.028.
Qadir, M., Quillérou, E., Nangia, V., Murtaza, G., Singh, M., Thomas, R.J., Drechsel, P. and Noble, A.D. (2014), Economics of salt-induced land degradation and restoration. Nat Resour Forum, 38: 282–295. doi:10.1111/1477-8947.12054
Swarajyalakshmi, G., Gurumurthy, P., & Subbaiah, G. V. (2003). Soil Salinity in South India: Problems and Solutions. Journal of Crop Production, 7(1/2), 247-275. doi: 10.1300/J144v07n01_09