Does Your Soil Act Like A Sponge?

Thursday, November 23, 2023

Increase Your Soil’s Water-Holding Capacity

For Long-Term Benefits

By Paul Hermans

Going forward as an industry the biggest limiting factor to higher yields will be water availability.

If you live anywhere in Eastern Canada, you may be saying this was not the case during the 2023 growing season. Across most areas for the growing season in Eastern Canada, we received 115 to 150 per cent more rain than average, according to Environment Canada.

Long-term however, we are seeing higher air temperatures and a general reduction of available soil moisture at critical periods in the corn and soybean crop’s lifecycle.

Let us look at how much water the crop uses, what are the critical periods for this water use, and how the root system explores the soil rooting zone for moisture.

Research data would say on average it takes about three thousand gallons of water to produce a bushel of corn. For soybeans it is three times as much! Textbook information would say corn needs about eleven inches of water to get through to the R1 (flowering) period from planting. Demand goes up for the last 60 days using another 15 inches of water. The critical periods for corn are the two weeks before and after pollination. For soybeans, the month of August is the most critical.

Thinking back over the years, this means from about July 1 through the end of August we need ample soil water reserves to achieve the highest yields for both these crops.

You would think this all has to come at the right time in the form of rain. But luckily, each crop sends down roots exploring the soil reserves looking for water and nutrients.

For corn, roots can achieve depths of up to four feet or deeper depending on soil texture and structure. Studies have shown that 40 per cent of soil water extraction occurs in the first 25 centimetres of soil depth and 70 per cent in the top 50 centimetres of soil depth. About 25 per cent of water availability occurs between 50 and 75 centimetres depths and the remaining 10 per cent at depths greater than 75 centimetres. However, the key is ensuring our root system can get access to this water. Soybeans, on the other hand, place 70 per cent of their roots in the top 25 centimetres of soil. Hence a reason soybean responds to timely August rains, adding yield in the form of less pod/seed abortion and larger seed size.

Research studies have shown that if we want to increase yields, we need to increase biomass production. The two go hand in hand. With higher biomass and subsequent grain production goes higher seasonal evapotranspiration.

This is where root structure and development come into play. Yes, there are differences in hybrid genetics when it comes to roots. Soybean roots are important as well. Oddly enough we have root scores for corn but not soybeans. Something we should explore as an industry to further develop soybean yields.

Improving soil health, structure and organic matter will also go a long way to helping corn/soybeans explore all the soil zone for water and nutrients. It is the fine root hairs that accept water and nutrients. Root hairs live only about five days and then replenish. Ensuring adequate soil moisture and sound soil health is key.

Let us do a deeper dive, looking at a variety of management practices you can incorporate to increase yields as it pertains to “drought proofing” your crops.

Soil fertility

Potash (K) plays an important role in the opening and closing of stomates which helps regulate plant temperatures and water loss. Most potassium and phosphorus move into the plant through diffusion, moving from areas of high concentration to low. Having adequate soil K levels will mean higher K movement potentially existing in the field to help regulate the plant during stress periods.

Organic matter

Improving soil organic matter and soil health will assist with deeper rooting depths and water-holding capacity. Increasing organic matter from two to three per cent, as an example, will allow the soil to hold about 3,400 gallons per acre on a silt loam soil, according to the University of Nebraska. That equates to over 1/10th of an inch of rain. Studies have shown that available water is double at soil organic matters of 4.5 per cent compared to 1.5 per cent (Hudson, B.D. Soil organic matter and available water, J. Soil Water Conserv. 49(2): 189-194).

That may not seem like a lot initially. But over subsequent rainfalls and during critical water shortages it can add up.

Cover crops assist in adding organic matter back to the soil while improving soil tilth and aggregate stability.

Crop rotation

Dr. Dave Hooker at Ridgetown College has conducted some unique long-term crop rotation studies. Overall results showed that crop rotations utilizing a corn-soybean-winter wheat rotation had greater yields increases than a corn-soybean rotation, especially during hot/dry summers or during seasonal trends when water availability was decreased.

Controlled drainage

More interest from growers is occurring, looking at utilizing controlled drainage during critical periods to improve water availability. These low-cost methods can improve root zone moisture. Constant monitoring is needed, especially during heavy rainfall patterns, to avoid “drowning” the crop.

Added to this reduced tillage, strip-till/no-till experienced larger yield differences in drier summers as well.

In summary, we have no control over the weather. We can however control crop management, species diversity and other factors to improve soil water holding capacity which will lead to higher yields in the future.

These gains are incremental and do not happen overnight or even over a single cropping season, for that matter.

Sitting down and producing a long-term farm field and sub field plan is needed to achieve the goals described above. Doing so will mean your valuable soil acts like a sponge, dripping with moisture when really needed! BF