Rajan Dhakal, Krishna P. Paudel, Matt Fannin and Naveen Adusumilli

Water and soil salinity affect food production and food security worldwide. Water salinity is a causal factor for soil salinity. Soil salinity beyond a certain threshold level can be detrimental to crop production. Soil salinization occurs when salt accumulates in the upper layers of soil, and it is generally prevalent in areas where evaporation exceeds precipitation, mostly in water-deficit conditions. In the U.S., about 12.8 million acres of agricultural land under irrigation have been affected by salinity. In this study, LSU AgCenter researchers focus on agricultural production areas overlying two aquifers — the Mississippi River alluvial aquifer, which is in the northeast part of the state, and the Chicot aquifer, which is in the southwest part of the state — to understand the potential effect of salinity in Louisiana.

Both the Mississippi River alluvial aquifer and the Chicot aquifer play a significant role in Louisiana agriculture. Understanding the economic effects of soil salinity in agricultural lands is vital because a detailed knowledge of possible effects of increased soil salinity conditions is essential for planning farming practices in salinity-affected regions of Louisiana. Because farm soil salinity in Louisiana is mainly irrigation induced, this study investigated the effect of saline soils on the yield of three major irrigated crops: rice, corn and soybeans. The study also explored the economic effect of some alternative cropping systems that can be adapted to prevent the adverse effects of increased salinity.

The Mississippi River alluvial aquifer and Chicot aquifer together are a major source of groundwater for 41 Louisiana parishes. For this study, however, the researchers considered only 17 of the 41 parishes because those are the areas where farmers irrigate rice, corn and soybeans. A two-stage approach assessed the economic damage of salinity to crop production. The first stage looked at the trend of increased salt content within these aquifers in order to predict the future level of salinity. Future salinity conditions were estimated based on previous data and studies by the U.S. Geological Survey and other researchers in Louisiana. Three scenarios representing three potential rates of increase in salinity were assumed: low, medium and high, in which the salinity level in these aquifers rise at a rate of 5 ppm, 20 ppm and 50 ppm per year. These assumptions were then used to estimate the salinity level of two aquifers in 10, 20 and 30 years. This provided nine scenarios to explore.

The threshold salinity model was used to determine the relative yield of selected crops in these nine scenarios. Results show that even a medium increase of 20 ppm in salinity in these aquifers can be devastating to the agricultural production of the region. Researchers estimate that in the 30th year, the high rate of salinity rise could reduce rice yield in the Chicot aquifer region by more than 39 percent and corn yield in the Mississippi River alluvial aquifer region by more than 60 percent, if no preventive measures are adopted and if salinity increased as projected. Soybeans also showed a similar trend in yield loss under high-salinity levels.

In the second stage, the researchers used a software program to estimate the potential economic effect from the increasing levels of salinity. The total economic effects of salinity-induced crop yield losses were estimated for the economy of the regions and the state for each scenario. To estimate the potential economic effect to the 17-parish regional economy, the researchers set a baseline economic scenario and compared it with the economic contribution of future crop production under increased salinity conditions. The baseline scenario in this study is the current total economic contribution of irrigated crop production (rice, corn and soybeans) in the 17-parish region, which is approximately 6,700 people employed and $1.13 billion in total output generated. By comparing the baseline scenario with a 30-year projection, the results show increased salinity can result in a loss of more than $500 million in total output and more than 3,000 jobs. However, adoption of alternative cropping systems such as the use of salt-tolerant crop varieties, switching to a nonirrigated system and switching to other salt-tolerant crops (cotton, sorghum and wheat) can significantly reduce the loss due to salinity. By employing alternative measures, the economic loss due to salinity with respect to the baseline scenario can reduce job losses by more than 35 percent and output losses by more than 20 percent.

Clearly, water and soil salinity need to be addressed in Louisiana’s breadbasket regions.

Rajan Dhakal is a graduate assistant; Krishna P. Paudel is the Gilbert Durbin Endowed Professor; Matt Fannin is the J. Nelson Fairbanks Endowed Professor; and Naveen Adusumilli is an assistant professor, all in the Department of Agricultural Economics and Agribusiness.

(This article appears in the winter 2019 issue of Louisiana Agriculture.)

The study area includes row crop production overlying MRAA and the Chicot aquifer. Note: According to the U.S. Geological Service, Louisiana has 13 major aquifers or aquifer systems (Red River alluvial aquifer, Mississippi River alluvial aquifer, upland terrace aquifer, Chicot aquifer system, Chicot equivalent aquifer system, Evangeline aquifer, Evangeline equivalent aquifer system, Jasper aquifer system, Jasper equivalent aquifer system, Catahoula aquifer, Cockfield aquifer, Sparta aquifer and the Carrizo-Wilcox aquifer). Only two aquifers studied in this article are labeled in the figure, and the remaining aquifers are separated using different symbols.