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Increase water going into soil
Dr. Victor Martin

As of this March 23th the Drought Monitor is showing even more improvement. Our area and much of Western Kansas is now is out of even abnormally dry conditions. Part of Northwest and Southwest Kansas improved to abnormally dry and only the extreme western counties and parts of the next are in drought conditions. Rains after Tuesday aren’t included. The rains midweek were beneficial as wheat continues to progress, alfalfa is growing, and there should be adequate moisture for planting corn. The six to ten-day outlook (March 30 to April 3) indicates normal temperatures and below average precipitation. The eight to 14 day outlook (April 1 to 7) indicates below normal precipitation and above normal temperatures.  A decent forecast for wheat and preparing for spring planting.  

Last week we discussed Soil Water: Part I, what determines the soil’s water holding capacity (soil texture and organic matter, amount of porosity and types of pores) and soil moisture terms (saturation, field capacity, permanent wilting point, gravitational water, plant available water).  Today, here are two more terms and what we can do to increase water going into the soil. 

• Infiltration – The source of soil water is precipitation. Infiltration is the process of water moving into the soil from the soil surface. You want the infiltration rate to be as high as it can be so precipitation isn’t lost to evaporation or runoff. The infiltration rate is highest at the beginning of a rainfall event and decreases to a steady state once all soil pores are full. That is determined by the saturated hydraulic conductivity. The saturated hydraulic conductivity is determined by several factors including total pore space, amount of macropores, and the connectivity of the pores. How do you maximize infiltration? Develop a pore system that includes large, connected pores by minimizing or eliminating tillage, eliminate soil compaction, having the soil covered by surface residues and a growing crop. Residues absorb the impact of rainfall which protects the soil surface, prevents soil crusting and slow down the rainfall.  

• Percolation – Once water is in the soil, its movement is termed percolation. Percolation occurs in all directions. In saturated soils, percolation is initially downward with gravity through macropores. Once these have drained, movement is confined to micropores. This water, held to clay and organic matter by adhesion can move in any direction, including upward against gravity, termed capillarity. Capillarity occurs only in micropores and the distance it can move upward against gravity is a function of pore size. The smaller the pore radius and the straighter it is, the higher it can move.

• Once last thing, water really doesn’t necessarily move from more to less water but from where the water has a higher energy potential to where it has less. So the water in wetter soil beneath drier soil has a greater energy potential and will move upward.

Next week: How do we maximize soil water holding capacity?

Dr. Victor L. Martin is the agriculture instructor/coordinator for Barton Community College. He can be reached at 620-792-9207, ext. 207.