Holding Soil Moisture

 

Farmers are finally getting moisture; rain, snow, and even ice. Recent rains followed by colder temperatures has restored some soil moisture. The slow steady rains have soaked in rather than running off. Waterways finally did fill up with water; but it took a long time. That is both good news for future crops planted next year, but also for water quality. Slow steady rains release much less nutrients into our waterways than fast hard driving rainfall events. 

Farmers do not know what the weather will be like this next year but hotter and drier summers are expected. Rain in summer generally makes grain, as long as it comes in moderation. An inch of fully used rainfall generally results in a minimum of 8-bushel corn, 3.5-bushel soybeans, and 6-bushel wheat. However, if moisture occurs when corn is tasseling (mid-July), soybeans are blooming (late July through mid-August) or wheat starting to bloom (mid-May to early June) expect higher yields. Moisture is critical for high yields because of a high nutrient demand needed for higher yields. 

Erratic weather is just accepted by most farmers. However, there are certain ways to maximize soil moisture to get higher yields. Irrigation helps, but its expensive and not everyone has a regular and dependable supply of water. Western farmers often receive less than 20 inches of rainfall per year and often fallow soil and do tillage numerous times to reduce weeds. However, tillage ruins soil structure resulting in excess water runoff, uses fuel, wears out machinery, and the water savings are quite small. In hot dry summers, a key goal is reducing evaporation and improving soil structure; so that when it does rain, the water soaks in. If 90% of the water runs off or evaporates, it does not do much good. 

Keeping soils cool reduces soil water losses by evaporation. A tilled bare soil may have a soil temperature as much as 500F higher than a soil covered with residue or plants. Getting crops planted early helps, especially if the crop canopy can be closed quickly. Early in the growing season, often the sun bakes bare soils. Recently, the hottest summer days seem to occur in June. Lately, August weather has been cooler but also dry. Extreme heat and a lack of moisture also stress our livestock, including soil microbes. Most nutrients become available when soils are slightly moist and microbes are working full tilt. When its hot and dry, microbial populations drop off dramatically and reduces nutrient release. 

Increasing soil aggregation or improving soil structure helps in several ways. Aggregates hold water due to increased soil organic matter (SOM) and root plus microbial exudates (glues). This allows beneficial fungi (AMF or mycorrhizae) to thrive. AMF store water and share that water with plants. 

Good soil aggregation also improves water infiltration and water storage when it does finally rain. Good soil aggregation requires lots of roots growing year-round. If you want proof, dig up a square of sod in your lawn or fence row and look at the soil aggregation. Aggregation reduces soil compaction for good air flow and keeps soil in place so that it does not erode away. Good soil aggregation also allows roots (corn, soybeans, wheat) to grow deeper to reach subsoil moisture. As soil structure and soil aggregation improves; soils become darker, gain SOM, and become more productive because they hold more water and nutrients. 

Good soil structure leads to improved water infiltration and less standing water. Our soils were very dry but the recent winter rains were fairly gentle and long lasting which allowed the water to infiltrate slowly. However, it is not uncommon to see water standing in a field when it rains only .5 to 1.0 inch. On soils with good soil structure and good aggregation, water soaks in and is released slowly. There are limits though, and well aggregated soils eventually fill up with water and leaves the field, although at a slower place. When soils are well aggregated, farmers save money on fertilizer leaving the farm due to less water and nutrient runoff. 

Crop residue on a field can be a blessing for reducing hot temperatures and conserving moisture, but in the spring, excess crop residue may reduce crop germination and growth. When soil health is good, 80% off your crop residue should be gone by spring. If it stays around for 2-3 years, it means your soil biology is poor and needs some attention. Unfortunately, it can take several years (3-7 years) to make that transition. Adding cover crops, no-tilling, and even a little manure can be beneficial to improving soil health and retaining moisture and nutrients.