Yield is Set Early—Are Your Water & Nitrogen Programs Ready?

The Big Idea: Water needs to be sufficient at planting time for seed imbibition, germination and development but dry enough to draw roots deeper in early-mid vegetative stages for later uptake. 

As we start to plan for the spring planting season, we should consider how soil moisture plays a part during early season development and how it can set us up for success (or failure) down the road. 

Certainly at planting we want the soil to be somewhat moist, to allow water to be taken up by the seed and initiate germination.  Likewise, we want additional moisture as temperatures increase and evapotranspiration takes off. 

Being too dry stops germination in its track.  In some more arid areas farmers must plant deeper than the typical 2 to 2.25” inches to access moisture.  In more humid areas, this isn’t a problem. 

Likewise, too much moisture at planting does no good.  Saturated soils, without any oxygen, make it difficult for seeds to germinate and get established.  Saturated conditions can also create anerobic conditions where certain bacteria thrive and convert free nitrate to nitrous oxide and later atmospheric nitrogen gas, losing valuable pre-plant applied nitrogen. 

Instead, a middle situation, where soil is moist but not saturated, is ideal, both at planting and the next 30-40 days.  Soils in this moist state, called field capacity, thrive in biological activity.  While ammonium nitrogen is easily converted while soil temperatures are warm and soil moisture is around field capacity (called nitrification), so is mineralization, the conversion of soil organic matter to ammonium nitrogen.  These conditions are ideal for early-stage corn. 

Non-saturated conditions also cause the developing corn plants to root deeper in search of more water, and along the way, nutrients.  This allows it to access supplies at deeper levels than if the soil had been saturated.  This sets the plants up for success later if a period of little to no rain occurs; roots are already deeper, accessing subsoil moisture.  During saturated conditions early on, roots will be much shallower and thus will not be as resilient under drought conditions. 

Under rainfed conditions, there’s not a lot a farmer can do to manage early season water other than surface and sub-surface drainage.  In more humid areas tile drainage is often useful for removing excess water around planting season.  But, if conditions are too dry at or after planting, there’s not much that can be done until the next rain comes. 

In irrigated situations, the farmer can provide extra moisture early in the season if needed, but because of likely being in a semi-arid region, water can be withheld to cause roots to grow deeper.  Then, when the ET demand is higher than the natural precipitation, the irrigation can be turned back on again and maintain the soil as close to field capacity as possible. 

In the next two articles, we’ll explore early season water and nitrogen management further.  Water and nitrogen go hand in hand, and using the available management tools and techniques can help conserve water, reduce nitrogen loss, and increase yield and profitability. 

Stay tuned for more tips and information.