Tile Drainage Reduces Salinity

Drainage_figure

Increasing salinity (salts) has been a big problem in many areas the past 15-20 years. Excessive rainfall and poorly drained soils are a bad combination. These two factors are a big part of the reason salinity is increasing in our region. As the water table gets closer to the surface in wet years, water is wicked to the surface. Once the water evaporates, the dissolved salts are left behind on the soil surface and reduce plant growth and yield. If this situation occurs for many years, the soluble salts can accumulate on the soil surface to a high level and reduce crop yields.

Surface drainage along with tile drainage and continuous cropping are the only way to reduce the salt level in soils over time. There are no magical soil amendments that will reduce the salt level in soil (wish there were!). With good surface drainage, tile drainage and good crop growth, the water table is lowered. Once the water table is lowered, this stops the capillary action which brings water to the soil surface and reduces salinity over time.

AGVISE has been monitoring the salinity (salts) of a tile drained field near our laboratory in Northwood, ND since 2002. The salinity level in parts of this field were very high when it was tiled in 2002. In October 2002, the field was tiled and we established 10 GPS points to monitor the change in salinity over time. Each fall after harvest we collect 0-6″ and 6-24″ soil samples and test them for salinity and all other nutrients.

In the figure you can see that over the past 12 years the topsoil salinity has decreased significantly at site 2 and site 5. These two sites had the highest initial salinity of the ten sites. You can see in this figure that in the dry years, the salinity stayed the same or increased a little, but over several years, the salinity at these two sites has decreased greatly. The salinity has been reduced, because the tile drainage has lowered the water table and excessive rainfall has leached some of the salts out of the topsoil. Improving crop growth through the years has also helped remove more water from the soil profile each year, helping to keep the water table further from the surface. This field now produces high yields of many different crops without losing yield to salinity. We expect the salt levels in this field to continue to decrease slowly for many years.