Tuesday, March 22, 2011

Watering Potatoes Properly Prevents Problems.

Improper soil moisture during the development of the potato plant and tubers leads to numerous problems to include delayed emergence, bacterial seed piece decay and plant death, distorted tubers, small tubers, tubers with large lenticles, and hollow heart and growth cracks along with other problems.

The knobby tuber in this photo is just one of the results of improper water management.

During sprout development, the soil should contain 70-80% available moisture.  After emergence, the soil moisture should be maintained at 75-85%.  During tuber initiation and bulking, the growth period with the highest demand for water, the available soil water content should be maintained between 80-90%.  When the plants start to die in the fall, the moisture content can be allowed to drop to 60-65%.

So, how do you determine how much moisture is in the soil.  You could invest in tensiometers or soil moisture probes, or use the much simpler and less costly soil-ball technique. 

Tensiometers are plastic tubes with a porous end that is place in the soil down to the depth of the roots.  A gauge on top of the tube provides readings of the soil suction.  This represents the energy a plant must exert to extract water from the soil.  These devices require a great deal of experience to correlate the reading on the gauge to the moisture content of the soil.

Soil moisture probes are often inaccurate in western Colorado soils as they can be negatively influenced by soil salts and thus may not provide accurate readings.

The easiest way to determine the moisture content of the soil is by taking a handful of the soil near the root zone of the plant and squeezing it into a ball.  The publication at http://www.coopext.colostate.edu/TRA/PLANTS/soilmoist.pdf shows you how to determine the percentage of moisture simply by squeezing a ball of soil and comparing the results with the photos. Most people in western Colorado have silty clay loam so those are the photos you should look at.

For a list of places in Mesa, Delta and Montrose where you can purchase certified seed potato, check out http://www.coopext.colostate.edu/TRA/PLANTS/Sources%20of%20certified%20seed%20potato%20-%2018%20Mar%202011.pdf or give us a call at 970 244-1836 for a copy of the list.

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