Drainage and Soil Health
Dr. Vinayak Shedekar, Ohio State Drainage Specialist recently shared some information. He compared the last 30 years of subsoil moisture conditions and confirmed that soil moisture levels down to 1 meter (roughly 3 feet) are only about 5-10% of average levels. Streams are very low especially in Southeast Ohio, but also Northwest and Central Ohio. In Northwest Ohio, the advantage of heavy clay soils higher in soil organic matter (SOM) helps retain moisture better than other areas.
Dr. Shedekar also shared that 70% of all crop losses come from water extremes. Usually, excess water is problem and accounts for 50% of all crop losses, while dry weather accounts for 20%. Improved drainage helps remove excess water but also improves soil aeration. Roots need access to oxygen to burn carbohydrates and sugars for energy.
Some farmers are now installing irrigation to help with dry conditions. Farmers first need a good source of water. Rivers and streams can be a source but you have to be careful about surface water contamination with chemical runoff. Ponds and wells are also good water sources. Generally, irrigation needs a minimum water source of 200 gallons per minute (gpm) up to 500 gpm. A rough estimate is it costs about $1,500 to $2,500 per acre if irrigating a 100-acre field. The biggest cost generally is in the pump which costs around $50-$60 thousand dollars. Generally, expect to put on 5 inches per year with applications costs of about $2.50 per inch for surface water and around $5 per inch for well water, depending upon depth. For corn, expect around a 50 bushel increase in yield.
Dr. Shedekar also talked about the similarities between drainage and soil health. Both improve crop yields and both improve the economics and profitability of farming over time. Investing in drainage is expensive but you don’t get all your investment back in the first year. For soil health, often the cost to make the system work may be slightly reduced yields for the first couple years, then yields stabilize, then improve. Both require some time before the investment pays off.
Both drainage and soil health increase aeration. Soil health increases soil tilth through the formation of large soil aggregates and increased SOM while drainage removes excess water. Both, together allow oxygen and gasses to reach the roots. Extra SOM is produced by more roots which helps improve soil health. Drainage is mixed bag on SOM. Excess aeration may reduce SOM, but most of the time the better growing conditions improve root growth and SOM additions.
Other similarities include is that improved drainage and soil health improve fuel costs because wet soils (poor drainage) and poor soil health (poor soil tilth) require more fuel while improving these soil properties decrease fuel consumption. Surface water runoff and soil erosion both decline when drainage and soil health improve. On nitrates runoff (N runoff), it is a mixed bag. Drainage generally increases N runoff while cover crops, no-till, and increased SOM with improved soil health decreases N runoff.
Both drainage and soil health decrease surface phosphorus runoff (P runoff). However, research shows that the concentration of soluble reactive phosphorus at the tile outlet increases. Interesting, since SOM levels are higher, soil health may increase water storage, and reduced water losses. Since total P runoff is a function of both the P concentration and water runoff, actual P loads (total amount of P leaving the farm) is actually lower when soil health improves. Drainage is somewhat of a mixed bag, sometimes increasing, sometimes decreasing. Generally, almost all problems with high P runoff occur with large rainfall events (greater than 2 inches) when it comes down hard and fast and overwhelms the natural soil system.
On soil temperatures, good drainage generally warms the soil by draining off cold winter water. Under soil health, the extra residue and SOM generally keep the soil a little cooler in the spring. Over time, once the soil tilth improves (may take 3-7 years), large soil aggregates start to form and with improved soil health, excess water drain away. One large benefit of high SOM, it stores more water for dry conditions and it is a good source of plant nutrients for summer growth. Combining strip till with soil health helps improve soil temperature warmup in the strip, especially for corn.
Finally, both drainage and soil health decrease variability in crop yields. Crop yields are more steady and generally higher overall where drainage and soil health are improved. Both work together. With out good drainage, good soil health is hard to achieve and good soil health improves crop growth and yields under improved drainage.