ProCrop 1999

LOWER THE WATER TABLE AND LOWER SALINITY RISKS

The key to managing saline soils is to control the flow of saline water into the crop root zone. When the source of saline water is a shallow water table, the management tool is to lower the water table. Since drainage is seldom an option in North Dakota, the solution is to continuously crop, using late-maturing, deep-rooted crops in the rotation.

A crucial element in successful salt reduction in a continuously cropped system is to eliminate bare or black summer fallow. Water use efficiency of fallow ranged from only 0 to 18 percent of rainfall during a five-year study. The researchers found that some water evaporated, but some contributed to ground-water below 4 feet in depth. If the soil profile is dry enough, however, the loss to groundwater is minimal and certain soils would retain more infiltrated water in the upper 4 feet in the spring. The study found that fallowing in a loam-textured soil when soil moisture before planting was less than 4 inches in the top 4 feet did not contribute excess water to groundwater. Soil moisture levels of 4 inches of available water in the upper 4 feet in a loam soil is about 25 percent of field capacity. Extending this principle to a sandy loam would not be appropriate, since the possible water holding capacity of a coarser soil is often not much more than 4 inches, so significant rainfall is rapidly moved to deeper depths.

It would be rare to have soil moisture levels low enough in the spring that fallow would not result in seasonal losses of added precipitation to groundwater. When spring moisture levels are sufficient for crop production, the chances of salt reaching the rooting zone are very high and fallow should not be used.

A late-maturing, deep-rooted crop with salt tolerance would be a good choice to help lower the water table. Deep-rooted, salt-tolerant crops can use saline groundwater.

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