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April 2

The Extension Connection Column by Jeff Stachler

Soil Health Issues Causing Major Financial Losses

Soil salinity, sodicity and high magnesium (Mg2+) levels versus calcium (Ca2+) are some of the key soil health issues causing major financial losses every year in the NE part of our State.

Wet weather resulted in shallow groundwater depths and brought excess salts and sodium (Na+) causing sodicity into the topsoil, however, recent drier weather has not helped either there has not been enough free (gravitational) water to force the salts into deeper depths but due to increased evaporation, more groundwater has wicked up towards the topsoil bringing more salts and Na+ with it.

Soil salinity is caused by excess levels of water-soluble salts competing with plant roots for water resulting in drought stressed plants despite decent moisture levels. Soil sodicity is caused by Na+ not being present as a salt and is attracted to the negative charges of soil particles such as clay and humus. By forming a relationship with clay and humus, Na+, separates clay and humus from soil aggregates resulting in very dense soil layers. That process is called “dispersion”. Due to dispersion, soil pore space shrinks resulting in much slower water infiltration compared to the same soils not having dispersion. Higher Mg2+ levels compared to Ca2+ result in excessive swelling of soils. This shrinks soil pore space resulting in much slower water infiltration compared to the same soils not having excessive swelling.

The very first step to remediate these issues is to create zones based on the severity of issues, cropping history and landscape and take separate three to four feet deep soil samples from each zone in 12-inch increments. Each depth should be analyzed separately for Electrical Conductivity (EC), Sodium Adsorption Ratio (SAR) and pH by using “Saturated Paste Extract Method”. For calculating rates of soil amendments such as gypsum, the 0-12 inch depths should also be analyzed for Cation Exchange Capacity (CEC) by using “Na+ Saturation and NH+ Extraction Method”.

Once soil results are available, need for soil amendments should be looked at first. Soil amendments are best utilized in powder form and incorporated after spreading. If application is not economically and logistically feasible, plant a salt-tolerant annual crop or salt-tolerant perennial grass mix based on soil salinity (EC) and sodicity (SAR) levels. Good vegetative cover will reduce evaporation resulting in less wicking up of groundwater towards the topsoil. Good vegetation will also use excess soil water under wet weather and preserve more moisture in topsoil under drier weather.

Barley and oats are two annual crops that can successfully produce good stands and profitable yields on low to moderate salinity and sodicity levels (EC = 4.0 to 6.0 dS/m and SAR = 7.0 to 10.0 in the 0-6 inch soil depths) where sensitive crops such as soybeans will result in net loss.

 

However, once soil EC is more than 6.0 dS/m with a SAR of over 10.0, even barley and oats may not grow well. That is when planting a mix of perennial salt-tolerant grasses will be most beneficial. That mix could be Tall Wheatgrass, Slender Wheatgrass, Western Wheatgrass, Green Wheatgrass (AC Saltlander) and Russian Wildrye. Generally, a seeding rate of 8 pounds of all five grasses per acre is sufficient. In addition, mixing 1-2 pounds of a winter-hardy alfalfa have produced good results. They are planted best in spring or dormant planted in fall. Being perennial, grasses take about a year to get established and two years to suppress the weeds on their own. 

 

Since salinity and sodicity mostly show up on headlands along roadside ditches, in-field ditches and wetlands, planting 25-30 feet wide buffer strips of the above mentioned perennial salt-tolerant grass mix is the best way to minimize the spread of salts and sodicity. One can say that planting buffer strip means taking some land out of the annual crops, however, not only these areas lose money but the size of the saline and sodic areas keep getting bigger every year. An established perennial salt-tolerant buffer strip can not only provide better trafficability but grass roots will also intercept capillary water before it would wick towards the higher productive areas.

 

It is best to mow, hay or graze these grasses as when they are cut above-the-ground, roots grow deeper below-the-ground.      

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