Ag Instructor Vic Martin: Agriculture and the water puzzle

Great Bend Tribune
Published January 6, 2019

A new year and quite a change in weather from January 2018.  Certainly much wetter and over the last few days, temperatures have moderated.  No drought in the state with a few counties bordering Oklahoma experiencing dry conditions.  While there are certainly many meetings this time of year for producers, January is the relative calm before the storm for crop producers as they prepare for the 2019 cropping year.  It’s a good time to discuss what may be the major challenge facing Kansas agriculture, especially in Western Kansas, water.  First, a little background may help.  What is normal?  What is drought

Normal climate in Kansas varies greatly across the state.  The southeast corner of the state normally receives around forty inches of precipitation while at the Colorado border, twelve to sixteen inches is the long-term average.  The length of the growing season is similarly varied from approximately over six months in the southeast to a little over four months on average in the northwest.  Humidity, wind, and even cloudiness also vary across the state.  Potential evapotranspiration (PET), the amount of water lost from land and bodies of water and through plants if water wasn’t limiting also varies as the result of these climate factors.  PET is lowest in the southeast and increases as you move west and is highest in the southwest.  The reasons for this variability include changes in elevation, the rain shadow of the Rocky Mountains for western Kansas, the Gulf of Mexico, and the tracking of the jet stream.   All of this determines climate. 

For simplicity, let’s look at Western Kansas.  Here we are on the border of humid with semi-arid to the west.   Long-term, humid indicates a climate where overall the amount of precipitation equals or exceeds the PET for the year.  Water should be adequate overall for crops without extended periods of moisture shortage.  That doesn’t mean no plant stress but limited and short-term stress on average.  Remember this is an average and droughts will occur.  For the semi-arid area in the west, it denotes that typically, PET exceeds precipitation most years.  In English for crop producers, the demand for evaporation and transpiration exceeds the available moisture for significant periods during the year.  All of this determines a variety of factors from adapted crops to the proper varieties/hybrids for a region and many cultural practices such as planting date. 

Now, what is a drought?  There is no one totally agreed upon definition.  For a meteorologist it is a significant decrease from precipitation from what is normally expected.  Therefore, if we receive our normal 28 inches we aren’t in a drought.  In Southeast Kansas, that is only 66% of normal so a drought occurred.  For a hydrologist, it is a lack of surface and subsurface waters.  For crop production, it is a lack of soil moisture to meet cropping needs.  This is what the drought monitor from Lincoln Nebraska measures.  And for producers, it is much more complicated than this.  When rain falls matters as much as how much.  Temperature, wind, and humidity also factor in as does the cultural decisions a producer makes.

Next week, where does the water we use come from and who is using it?

January 13, 2019
Part II

Last week we discussed what normal is regarding precipitation and climate here in Kansas as well as what a drought is.  This week’s column discusses where water in the state is used and where does it come from.  First, something happened this week regarding water occurred.  As one of his final acts, Governor Colyer rescinded the emergency declaration regarding drought in the state citing improved moisture conditions and the fact that Kansas has been out of any drought conditions for over a month.  Good news indeed heading into 2019.

Where is our water used as a state?  Remember this isn’t counting rainfall directly but from aquifers, reservoirs, etc.  As a state, approximately eighty-five percent is used for irrigation, nine percent municipal, three percent industrial, and one percent each for recreation, stock water, and other uses.  However, that doesn’t tell the whole story.  Looking at it by region, especially county presents a different picture.  With the exception of a few counties such as Ford, Finney, Reno, and Barton, essentially one-hundred percent of the water used is for irrigation in the western two-thirds of the state.  Barton County is interesting as it is the only county in the west where recreational water usage is significant and that is water going to Cheyenne Bottoms.  The eastern third paints a different picture with several counties almost entirely municipal water usage and with a few exceptions, relative little or no irrigation.  And there are several counties such as Coffey and Linn more than half industrial.  This is breakdown is logical given state demographics One other item of interest is the total amount of water used.

With the exception of urban areas such as Wichita and the K.C. Metro, the most water used yearly focuses on Southwest Kansas and part of the northwest corner.  Naturally, water usage is highest where population centers are and where irrigated crop acreage allocations are highest.  Where does this water come from?

In much of Western Kansas where the irrigation is, it’s the Ogallala aquifer.  Some of it is surface waters like the Republican River and some from reservoirs such as Cheney Lake and Kannapolis. The source of that water varies.  For aquifers it’s percolating rainfall.  For reservoirs it’s stream flow into them.  For rivers like the Arkansas and Republican it’s tributaries feeding them.  Much of the Arkansas River water starts as snowfall in the mountains of Colorado. 

This is terribly brief but sets up next week’s column on the water challenges the state is facing.

January 20, 2019
Part III

Since this series deals with water, it’s appropriate to briefly discuss this winter’s weather.  Soil in the area is wet, quite wet and as this is being written, another winter storm is on the way.  Many soils are saturated and there are areas on standing water.  What does this mean for wheat in the ground?  On the plus side, unless the weather turns off exceptionally hot and dry, there should be adequate moisture for a wheat crop.  Are there concerns with standing water and saturated soils?  While not ideal, the damage should be minimal if standing water infiltrates into the soil before temperatures warm and wheat resumes growth.  There are two problems with standing water.  The first is the loss of nitrogen from the soil.  The second is a lack of oxygen necessary for root cells to respire and function properly.  Cold weather minimizes that need since plants aren’t trying to grow.  Time will tell how much damage may have been done.  Last week we discussed were the water use comes from – the surface and groundwater we use.  Today, were does that water come from?

Groundwater, is the result of the accumulation of water over hundreds and thousands of years in water permeable rock from precipitation.  This rate of accumulation is the result how much precipitation falls and the intensity of events.  Precipitation must be sufficient to not only infiltrate into the soil but enough to fill all soil pours – to saturate the soil – and allow gravity to push the water downward.  Most rainfall events don’t contribute to groundwater.  A secondary factor is the ease with which water can move downward.  That is a function of the soil type; movement is easier in sandy soils, and the composition of the water bearing rock.  There are other factors such as depth to groundwater, evapotranspiration rates, and temperature.  The accumulation of groundwater is a slow process.  The Ogallala aquifer, a large underground lake in western Kansas and states such as Colorado, Oklahoma, and Texas is critical in supplying water for an area prone to drought and heat.  As long as withdrawals from pumping don’t exceed inputs, the aquifer is fine.  When more is withdrawn than can be replenished you have a water deficit.  It is like a checking account.  You can’t take out more than you have and that is the direction the aquifer is heading towards.

Reservoirs are filled by runoff from precipitation flowing into them, typically from creeks and rivers.  Rivers receive water from runoff within the state and from states upstream such as Colorado and Nebraska.  Their flow is also determined by groundwater.  Permanent streams and rivers are groundwater at the surface so as the groundwater declines, so does the flow in the streams.

Next week: where are we at with water in Kansas.

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