The drought monitor report as of Tuesday, Nov. 5 shows improvement across the state. Barton County has improved some with the southeast corner now just abnormally dry. Stafford County and Pawnee also improved. Severe and moderate drought increased across the state. The six to ten-day outlook (Nov. 12 to 16) indicates a 50 to 60% chance of likely above normal temperatures and a 33 to 40% chance of leaning above normal for precipitation. The eight to 14-day outlook (Nov. 14 to 20) indicates a 40 to 60% chance of likely above normal for temperatures and a 40 to 50% chance of leaning above normal for precipitation. Good for the wheat crop.
We have finally received some moisture with hopefully more on the way. Things almost look wet. We have water in ditches and even a bit of standing water in the fields. This provides some hope but is the drought nearing an end? Hopefully you said no. Today, what is a drought and when is it over.
There are several definitions for drought. Maybe the easiest to understand is a drought is when less than 70 percent of normal precipitation is received. The drought monitor report printed here every week breaks it down from abnormally dry to exceptional drought. So there are really two factors here: how much of the average normal rainfall does the area receive (which changes every 30 years) and what is the status of soil and subsoil moisture. This has implications on crop growth and groundwater recharge. So, even though an area may be in severe or exceptional drought and then receive several inches of rain in a short period of time, you may not see much change in drought status. Why? How much of a dent did it make in the shortfall? And, how much helped in soil moisture recharge? Also factored in are evaporation and plant transpiration rates which are a function of temperature, humidity, wind speed and plant water use. Heavy rains now are more effective than say in July or August in replenishing soil moisture. The evaporative demand now is less and plant water needs are much lower.
How much precipitation it takes to replenish soil and subsoil moisture is a function of the soil type, soil structure and organic matter content. It takes less water to fill a sandy soil than a silt loam or clayey soil. Soils with higher organic matter levels hold more water. Soils with a better sore structure hold more water. No or minimum till soils lose less water due to evaporation. Subsoil moisture can’t recharge until the top soil is recharged and groundwater recharge doesn’t start until soil and subsoil moisture are replenished.
Extreme, high intensity rainfall events result in less effective precipitation than moderate, more long-lasting events as runoff is higher. Soil pores matter here as does residue cover. Soils with good residue cover and a well-developed large pore system are much more effective in soil moisture recharge. Events of a quarter inch or less aren’t generally effective as there is little infiltration into the soil.
Dr. Victor L. Martin is the agriculture instructor/coordinator for Barton Community College. He can be reached at 620-792-9207, ext. 207, or martinv@bartonccc.edu.
