By Mahdi Al-Kaisi, Department of Agronomy; and Mark Hanna, Department Agricultural and Biosystems Engineering
Current weather conditions and wet soils cause certain anxiety and concerns for late planting, especially for corn. Spring weather this year definitely creates challenges in preparing fields and getting certain field operations done on time, such as tillage, anhydrous injection, manure application, etc. Decisions to conduct these operations need to be made carefully regarding the soil moisture conditions. The current soil moisture status makes the soil conditions susceptible to soil compaction, low soil temperature and soil erosion just to name a few. These problems can be yield robbers. Let's discuss them individually and why we need to be more patient in entering fields and why waiting a few days may pay off significantly.
Soil Compaction and yield
Soil compaction can occur when soil moisture is at field capacity, where the soil retains the maximum amount of water as dictated by soil texture and natural drainage of that particular soil. The best way to determine if your soil is at field capacity is to check your tile drain. If it is still running your soil is saturated and you need to consider waiting before entering the field.
However, once the tile stops running then the soil is at field capacity. As a rule of thumb when soil is at field capacity, it is advisable to wait one to two days before entering the field, because at such conditions soil compaction and side wall compaction (when soil smeared by anhydrous knife or seed bed-openers) can be very significant and much deeper than at dry soil conditions. The reason for a high level of soil compaction at such moisture conditions is that soil aggregates will easily break down under a heavy load. The compression of soil particles will reduce soil porosity and reduce aeration that is essential for root growth and development and ultimately reduce yield.
One study documented 18 to 27 bu/acre losses when corn was planted into wheel tracks of a susceptible wet soil during spring field work. Although yields over time may be reduced 4 to 6 bu/acre for corn and 2 to 3 bu/acre for soybean, yield due to severe soil compaction from disturbed soil operation can range from 10 to 30 percent or more depending on the level of soil compaction. These conditions can encourage shallow root formation.
Another problem that may be associated with wet soil condition planting is the proper seed depth, which should be on average a 2-inch planting depth to ensure best root formation. Therefore, check planter settings often and proper closing of soil is essential to ensure a uniform plant stand.
Low soil Temperature
Excess soil moisture can significantly affect soil temperature, especially in poorly drained soils. The current moisture condition and the saturated soil profile caused significant drop in soil temperature from two weeks ago. Ideally, for optimum soil conditions for seed germination, soil temperature should be approximately 50 F or above at the top 2 inches. Some of the risks of planting in cold soils include a delay in germination and exposure of seeds to soil borne diseases that can have considerable impact on yield potential.
Soil erosion
Soil erosion is always a concern during this time of the year when soil, especially conventionally tilled fields, is most vulnerable without growing plant cover or residue cover, and exposed to rain intensity. Working soils during wet conditions can accelerate soil erosion due to soil compaction that reduces water infiltration and increases surface runoff. These freshly tilled soils are most susceptible to top soil loss during heavy rain events. It was documented that reduction of top soil depth (A-horizon) by 2 inches caused corn yield loss by as much as 2 and 5 bu/acre for loess- and till-derived soils, respectively.
Operating field equipment at suitable moisture soil condition is essential for maximizing yield potential and avoiding unnecessary soil compaction that can cause nutrient loss and deficiencies of nutrients such as potassium, and ultimately resulting in yield loss. Even delaying an operation part of a day to allow surface drying can make a big difference. Modern agricultural technology and equipment can make a difference in compensating for loss of time.
Mahdi Al-Kaisi is an associate professor in agronomy with research and extension responsibilities in soil management and environmental soil science. He can be reached at malkaisi@iastate.edu or (515) 294-8304. Mark Hanna is an extension agricultural engineer in agricultural and biosystems engineering with responsibilities in field machinery. Hanna can be reached at hmhanna@iastate.edu or (515) 294-0468.
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