ISSUE 1 May 4, 2000EXPANSION OF SALINE AREAS
There has been a great deal of interest in the greater expanses of white saline areas in fields this spring. One reason for their appearance is that these areas have been present in the past couple years, but the soils have been moist enough so that the salts have not shown up. The main reason that these areas are present is due to the above normal rainfall/snows over the past six years.
Salt comes from our groundwater. When groundwater is deep, as it is during dry periods such as 1987-1989, the areas of salinity are reduced in size, because what water does fall moves the salts deeper in the soil. However, when the water table is within 3-4 feet (as it is in many areas-just ask the local soil sampler) salts are carried to the surface through capillary action, the water evaporates and the salts are left behind.
There is a lag time between rainfall and groundwater accumulation, and a lag time between this accumulation and groundwater lateral movement. So even though it has been relatively dry in some areas since last summer, most pond/stream levels and the groundwater levels have not decreased significantly. In addition, because rains have been spotty this spring, there has not been significant leaching of salts either.
In many fields, the salts are encroaching from the road. If a strip of alfalfa can be established along the ditch,(about 30 feet wide is usually enough) this is usually enough to lower the water table and prevent higher groundwater and salt encroachment into the field.
In our region, nodule development and nitrogen-fixing bacteria activity in inoculum is relatively slow. Part of this reason could be our increased stress on the soybeans due to chlorosis. Research in Crookston has shown that some N at planting time can increase yields. Because of these factors, if soil test N is below 50 lb/acre at the 0-2 foot depth, then applying enough N to increase the N supply to 50lb/acre would be justified.
Phosphorus should be applied if soil test levels are low and very low. Phosphorus applied at these levels performs best if broadcast. With our air-seeders, it is certainly physically possible to apply P with the seed if levels are not too high, but to achieve yield increases worthy of the effort, broadcast application should be made.
Soybeans are not sensitive to low zinc levels like dry beans or corn. Tests of zinc application on soybeans have been made often in South Dakota and Minnesota with very little benefit of zinc application. One large test in North Dakota also showed no benefit to zinc.
Recent work in North Dakota and Minnesota has shown some benefit
with chlorosis tolerant varieties (not intolerant ones) to application of seed-placed iron
fertilizers. However the research is very preliminary and second year work by the North
Dakota researcher showed no benefits as compared to the first year work. One cultural
practice that decreases chlorosis is planting in wider rows as compared to solid seeded.
Planting in 22-30+ inch rows appears to decrease chlorosis and
allows for early cultivation to help dry out the soil and lower soluble bicarbonate levels.
In new soybean areas, be aware of soil carbonate levels and soluble salts. If soil carbonate levels are above 1%, then serious chlorosis is possible. If salt levels are above 1.5 mmoh/cm, then soybeans may not be the crop for you.
Dr. Dave Franzen
NDSU Extension Soil Specialist