Stu Ellis: Did The Drought Hurt Your Soil?

By Stu Ellis,  Farmgateblog.com

Measuring the drought impact on your 2012 yields may have been easy, although the psychological impact cut to the quick.  However, more difficult may be measuring the impact of the drought on your main asset, the soil on your farm.  Sure, it dried out as heat increased and rain diminished, but how was it impacted beyond the loss of moisture?  The soil itself suffered physically and that is something that needs your attention.  After all, it may have a $15 to $20 thousand dollar per acre value.  With that value you cannot afford to have it break, because baling wire and duct tape won’t help much.

The impact of a drought is typically measured in terms of loss of moisture, and the weekly Drought Monitor from the University of Nebraska kept everyone informed of whether they were in the yellow, brown or red territory, and how bad it was in their state.  But just like moisture being only one characteristic of grain, it is only one characteristic of the soil.  Grain can be dried to manage moisture, and soil moisture can be managed to some degree as well.  But how is that done and what other issues did the drought create?  Those questions are addressed by Iowa State University soil scientist Mahdi Al-Kaisi and a number of his colleagues in the Journal of Soil and Water Conservation.

The Iowa State researchers reported that drought conditions, which were pervasive throughout their state, caused fracturing and cracking in the upper 6 to 15 inches of the soil, with the potential for deeper cracking depending on soil minerals and clay content.  They report soil crusting was a problem as surfaces hardened  where conventional tillage had been used and where there was poor cover from either residue or crops.  Problems began to appear in the winter of 2011-2012 where a lack of surface cover caused deterioration of soil aggregates, allowing cementation to occur that impacted the relationship between soil moisture and plant roots.

Damage to the soil itself

Al-Kaisi reports that soil management practices can improve the way water is stored in the soil, and when available for plants, it will reduce the impact of the drought.  Such management practices will enhance the soil aggregation, water storage, water infiltration, and reduce potential erosion, all with management techniques:

Tillage of dry soil damages soil structure, and when moisture is available the moisture will not be held in the soil and will result in erosion.  Tillage also reduces the ability of moisture to reach the subsoil where it would be available for crops in time of moisture stress.  Consequently, he says either no till practices or minimum tillage will decrease the impact of a drought.

Residue management can play a significant role in sustaining a good soil structure.  Surface residue retards erosion in heavy rain, and good residue will allow more water to enter and remain in the soil profile.  He says allowing 12 in. of corn stubble to remain will achieve those objectives.  He adds, “Upright residue traps and stores moisture effectively and slows downslope water movement.”

Cover crops will protect soil from erosion, improve the soil structure, increase organic matter, and reduce nutrient loss.  But he acknowledges that dry conditions from a drought may challenge the ability to get a cover crop established.

Agronomic lessons learned from the drought

Al-Kaisi and his Iowa State colleagues identified several additional agronomic lessons that were learned from the 2012 drought:

• Crop residue retention with no-till systems improves water infiltration rate and conserves soil water content by reducing soil cracking and crusting and preserving soil structure.
• Corn following corn suffered greater yield losses than corn following soy­bean. Continuous corn typically does not yield as well as corn after soybean, but the yield differential was much greater in 2012.
• Cover crops can accumulate residual NO3-N, thus decreasing losses from the root zone. Much of the N accrued in cover crops will become available to subsequent crops.
• The reduction of corn plant growth and grain fill during drought led to high NO3 accumulations in vegeta­tive plant tissues, particularly in the lower corn stalk. Testing corn silage or baled stalks was important in 2012 to determine if NO3-N levels were safe for livestock.
• Corn N fertilization rates necessary to provide optimum yield typically are lower in years with below-normal rainfall. This effect can persist across multiple years of dry conditions, even with a return to normal rainfall. Therefore, effects of dry conditions should be considered in decisions for N application rates to 2013 corn crops.
• Corn silage harvest results in greater P and K removal than grain harvest alone since most of the aboveground plant is harvested. This increased removal rate from grain-only harvest should be considered in nutrient plans for subse­quent crops.
• Dry fall conditions can impact soil test results. Predicting nutrient availability during drought is difficult. Sampling after fall rainfall occurs or sampling in the spring improves soil test reliability.
• Drought revealed that genetics may have a limited role in protecting yield without optimum moisture availability in the absence of an integrated crop management system. Significant root­worm feeding damage was observed in 2012 on hybrids with Bt rootworm resistance. Decreased root volume fol­lowing root pruning results in lower water use under drought conditions, more crop stress, and reduced yields.
• The jury is still out on drought-toler­ant hybrids. Unfortunately, results of scientifically valid comparisons of sim­ilar genetics with and without drought tolerance are not yet available.
• Planting a range of hybrid maturi­ties will help spread risk, but plant only hybrids adapted to your area. Non-adapted hybrids may have neither the yield potential nor disease resis­tance of adapted hybrids.

Summary:

While the drought could continue in some portions of the Cornbelt in 2013, some good lessons have been learned that may help prevent a recurrence of poor yields that resulted from a lack of drought management.  Damage to the soil in drought conditions can occur from tillage, which breaks up soil structure and reduces infiltration of rainwater, preventing it from getting to the subsoil.  Allowing more residue to remain on the soil surface will help retain moisture and improve moisture infiltration; and the use of cover crops will retain moisture, provide livestock feed, and retain soil nutrients.

Source: Farmgateblog