Despite the 5,000 year –or so – history of agriculture, does our contemporary agricultural community take heed on the lessons learned from the past on the causes of agricultural topsoil salinization?
By: Ringo Bones and Vanessa Uy
The serious – though preventable – problem of agricultural topsoil salinization is as old as the practice of agriculture itself, it seems like we at the present are not trying as hard as we should in preventing such problems. Especially by ignoring on what we had learned in the past about the phenomena of salinization and doing it in our peril. Is the problem still relevant in 2008 given we had learned so much before?
The Girsu Documents of southern Iran, which dates back 4,300 years, showed accounts on the progressive salinization of cultivated lands. The documents mentioned how the rich farmlands of Mesopotamia, in what is now Iraq, were ruined by irrigating them using the brackish water from the Tigris and Euphrates rivers. Wheat was once cultivated on a large scale but by 2,400 BC farmers turned to barley, which is more salt tolerant, as an alternative crop. Seasonal floods, which raised the water table, increasingly salted the topsoil. By 2,000 BC, even barley began to fail. Eventually the land was abandoned and the water table dropped, leaving a salt saturated desert where no crops can grow.
Typical of the alluvial plains of Mesopotamia and the rest of the Middle East, as in any dry area, there is relatively prodigious amount of salt in the ground because rain water, or even water in the surface soil, evaporates before the salty minerals has a chance to leach out. Therefore, any rise in the water table will lift up the salty water up to the surface soil. Seasonal floods, which cover large areas with standing water, can also cause such a rise. Our “start up” farming methods of centuries past has actively created such a situation in arid regions for centuries by digging a number of irrigation canals which continually silt up and overflow onto the surrounding land. Furthermore, in very hot and arid lands, the thirsty soil can actually suck up salty water from below via capillary action during the long, dry spells.
Despite the great havoc wreaked on the land before we learned better agricultural management, there is still hope that some areas – seemingly beyond salvation – may yet be brought back to full productivity via proper irrigation. A cause for hope is the fact that in most arid regions, rain has not yet leached the valuable surface minerals from the topsoil. At the same time, however, there is a concern that conventional irrigation methods will raise the water table and in doing so bring increasing amounts of harmful salt to the fertile surface through capillary action.
Years ago, a program was tried in Afghanistan (this was before the Soviet invasion and the subsequent Taliban takeovers) to combat and reverse salinization by flushing the fields with water to wash out the crystallized salt. And also deep drainage ditches were dug to assure that the water table stays below a safe minimum. Additionally, tamarisk trees were also planted. Tamarisk trees are salt tolerant plants and are being used to restore Afghan soil and these trees also sop up excess water thus guarding against further salinization.
The agricultural regions surrounding the Aral Sea and the Aral Sea itself was also a relatively recent victim of agricultural farmland mismanagement. Several rivers that fed the Aral Sea were diverted by the then Soviet Union to cotton fields used in the large scale production of nitrocellulose or guncotton (smokeless powder) to beef up the nation’s Cold War era arsenal. It was only in the last couple of years or so that existing programs were seriously involved in restoring the Aral Sea and the surrounding communities. Like the International Aral Sea Rehabilitation Fund – have shown favorable progress. But their work won’t be easy because the agricultural lands surrounding the Aral Sea not only suffer from salinization, but also contaminated with toxic pesticide residue left over from the chemically intensive Soviet era agricultural methods.