As last year has certainly shown most of us, water is one of the biggest drivers of success or stress in a cropping system. Not only is it difficult to manage something so unpredictable, but sometimes the things you do to keep water in your fields during a drought are the same things that can turn the field into a muddy mess for weeks. 

There is no one-size-fits-all water management technique, but there are options that can help you be more prepared for different water-based challenges. Cover crops are one of those options; they influence how water moves into, through, and out of our soils. Understanding how water moves in a cover crop system can help you manage new risks and opportunities, and determine what strategies are right for you.

UNDERSTANDING WATER IN THE FIELD 

When rain hits a field, several things can happen. The balance between them determines whether that rainfall becomes stored soil moisture, or a problem that can delay field operations. 

Infiltration  

• Infiltration is the rate at which water enters the soil surface - when rainfall intensity exceeds the infiltration rate, water will begin to pond and flow across the surface instead of seeping into the ground 

• Good infiltration depends on soil structure, surface cover, organic matter, and amount of soil compaction - soils with stable aggregates allow water to infiltrate more effectively 

Retention 

• Once water infiltrates, the next question is how much stays around where plants can use it - soil organic matter is key here, with higher organic matter content resulting in more water retention potential 

• Think of soil organic matter as a sponge - not only does it let your field absorb water, it also helps it keep it long after the rain has stopped Runoff 

• Runoff can occur when rainfall exceeds infiltration, or when soils are fully saturated - runoff doesn't just carry off water, it can wash away soil, nutrients, and pesticides too 

• Bare soils are particularly vulnerable to runoff, because there's nothing in the way to slow the water down or protect the surface from heavy raindrops (which can contribute to crusting) 

Evaporation / Transpiration 

• Water also leaves fields through: Evaporation (from the soil surface) or… Transpiration (through plant leaves) 

• Sometimes these processes are lumped together as "evapotranspiration" - bare soil tends to lose water quickly through direct evaporation, especially in windy or hot conditions 

HOW COVER CROPS CHANGE THINGS 

Infiltration? Increased 

• Cover crop roots create channels for water to flow underground, surface residue protects soil from crusting, and roots support soil microbes that bind soil into stable aggregates 

• This all leads to less ponding after rainfall as more water ends up beneath the soil surface University of Minnesota Extension notes that fields with cover crops report dry field conditions much more quickly after a rain event than bare fields 

Retention? Increased 

• Cover crops add biomass above and below ground that increases soil organic matter over time, especially with long-term repeated use 

• By increasing the size of the organic matter "sponge" you can improve your drought resilience 

Runoff? Reduced 

• Cover crops and their residue slow down water movement across the soil surface and protect against raindrop impacts 

           - According to SARE, cover crops reduce sediment loss by an average of 21 tons per acre on conventional-till fields 

• This keeps more soil and nutrients where they belong (in your field instead of the nearest creek) 

WHAT IF WE GET ANOTHER SUPER WET SPRING? OR THE OPPOSITE? 

Last year we saw a particularly wet spring followed by a particularly dry summer, which caused several issues for growers across Upstate New York. Here's some management considerations in case this year ends up mirroring the last, or if it flips the script: 

• In a wet spring, cover crops can help remove excess water through transpiration, while also improving soil structure and allowing for better infiltration instead of ponding 

         - In this case it would be wise to wait a bit later to terminate the cover crops to allow for extra water removal (this may happen                by accident if the fields are too wet to access anyway) 

• In a dry spring, cover crops might end up depleting stored water, leaving less for the main crops going into the summer, though the soil structure improvements will still occur 

          - In this case an early termination might be helpful, especially if the termination leaves residue that can further prevent                             evaporation