One of the best visualizations I’ve heard for managing your soil moisture and the precipitation you receive is to compare your soil’s moisture-holding capacity to a bucket.
The size of your bucket depends on soil texture, organic matter content and soil structure.
With good surface residues you can get the precipitation you receive to infiltrate the soil and start filling the bucket.
If you have good soil structure you can get the moisture to the bottom of the bucket, and if you have good organic-matter content your soil will act as a sponge and have a larger water-holding capacity.
The idea of a good continuous no-till crop rotation is to fill the bucket as much as possible between crops, then grow a crop to utilize the moisture in the bucket.
The soil is like a bucket in that it won’t hold any more water than it has the capacity to hold, so there isn’t any advantage to trying to add more water to it when it’s full.
To keep the water in the bucket and not let it evaporate out, you can put a cover on it to slow down the evaporation. Surface residue from previous crops provides the same cover for the soil and slows down soil moisture evaporation.
A neighbor of ours who is beginning to no-till recently shared an interesting experience with me. He chemical fallowed a winter-wheat field a few summers ago and planted this field to dryland corn this spring.
This field had a fallow period of almost 22 months from the time his winter wheat crop was harvested in July of 2010 until he planted the corn in May of 2012.
My precipitation records on our farm would indicate he had 27.57 inches of precipitation during this period. His soil moisture bucket overflowed: The corn crop had 3.43 additional inches of precipitation after planting to maturity. This is a total of 31 inches of precipitation during this time.
He also planted dryland corn on other fields following a previous year’s winter wheat crop. This corn received 10.69 inches of precipitation during the fallow period from July of 2011 until May of 2012.
The corn also had the additional 3.43 inches of precipitation during the growing season. This gave the continuous no-tilled corn 14.12 inches of precipitation to produce grain.
The field that was fallowed for 22 months and planted to corn was his poorest yielding field of corn this year despite the additional fallow period.
My neighbor’s conclusion was that the lack of residue on the soil surface because of the extended fallow period was the reason for the lower yields. The residue from the 2010 wheat harvest deteriorated to the point that he didn’t have a good cover on his bucket.
Despite the long fallow period, which was used to store additional moisture in the soil, the lack of residue on the soil surface proved detrimental and ultimately determined the fate of the poor-yielding corn.
The Whole Picture
My neighbor learned the value of residue on the soil surface when it comes to grain production in our region. Continuous no-tilling better utilizes the moisture we receive and better manage our bucket of water.
With a full bucket of moisture, good residue cover on the soil surface and a few timely rains, we can put the moisture that we have stored in the bucket to good use and produce good yielding crops.
The amount of residue on the soil surface was more influential in determining the crops success than the extended fallow period. This benefit of residues on the soil surface applies whether it is dry land or irrigated crop production and helps slow soil moisture evaporation.