As of April 5, the area of extreme drought that covered most of Barton and part of Stafford County stayed the same but the area of severe drought is expanding. Over 60% of the state is at some level of drought with another ten percent abnormally dry. The six to ten-day outlook (April 13 to 17) indicates a 50 to 60% chance of below normal temperatures and normal precipitation. The eight to 14-day outlook (April 15 to 21) indicates a 40 to 60% chance of below temperatures and a 33 to 40% chance of below normal precipitation. Not what wheat producers or spring row crop planters want to hear. And with this outlook, it’s a good time to look at how temperature and moisture affect crop nutrient uptake.
Except for carbon, hydrogen, and oxygen, the remaining essential plant nutrients are taken in by plants through the root system in inorganic forms. There are three methods of nutrient uptake by roots:
• Mass flow – As roots take up water from the soil, nutrients such as nitrate, sulfate, and chloride are carried along to the roots.
• Root interception – Only actively growing roots and root hairs produced on mature root tissue take up nutrients. This is where the root runs into the nutrient as it is exploring the soil volume.
• Diffusion – Here, nutrients such as calcium and phosphate move along a concentration gradient for higher to lower concentration. So when the root extracts these nutrients it causes them to move towards the area where the root has removed them.
So why do temperature and soil moisture matter in nutrient uptake?
• Roots must continually explore the root zone to take up water and nutrients. Roots can’t grow through dry soil. Second, plants only take up nutrients in the soil solution. Third, nutrients adsorbed to the soil complex (clay and organic matter) are held more and more tightly as soil moisture levels decrease. So drier/dry soil impedes nutrient input even with adequate soil fertility by interfering with mass flow and root interception.
• Cool spring soil temperatures interfere with uptake in several ways. First, diffusion of nutrients like phosphorus (P) slows down in cool soils which is why corn often looks P deficient, even with banded P, until the soil warms. Second, it is often minor but water becomes more viscous under cool temperatures and moves a bit more slowly to the roots. Third, root growth is slowed by cool soils which decreases root interception.
• Lastly, cool air temperatures slow above ground growth which decreases the amount of energy for the roots to grow and development.
In summary, nutrient deficiencies are often visible in wheat and spring planted crops even with property fertility. All a producer can do is insure nutrients available at the right time, in the right form, and in the right place.
Dr. Victor L. Martin is the agriculture instructor/coordinator for Barton Community College. He can be reached at 620-792-9207, ext. 207, or email@example.com.