|Lamb, John - UNIVERSITY OF MINNESOTA|
Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 9, 2000
Publication Date: N/A
Interpretive Summary: Many recent agronomic practices call for the placement of fertilizers and chemicals in bands next to the row to help limit total chemical application and increase fertilizer use efficiency. Rainfall and irrigation falling on bare soil surfaces will generally be uniformly distributed over areas with and without applied chemicals. However, little research is available describing how growing plant canopies redirect incoming precipitation. Th improper placement of agrichemicals on soils where rainfall is concentrated by the plant canopy may well increase chemical losses, leading to ground water pollution. To address this concern, rain and/or irrigation were collected at points between corn rows over a 4 year period. Soil samples taken at the same points revealed the resultant soil water content after rain and irrigation events. The combination of plant canopy stage of growth, wind speed and wind direction all influenced where precipitation entered the soil surface between the rows. As plant canopies increased in size, over half of the incoming precipitation was directed by the canopy down the corn stalk, by-passing the zones of agrichemical application. Furthermore the canopy acted as an umbrella allowing less water to enter the soil in the area where herbicides are band applied near the plant. As a result, producers, crop consultants, and outreach scientists may use this information to refine agronomic practices such as chemical placement, row spacing and orientation to reduce the undesirable environmental impacts of agrichemical leaching to groundwater.
Technical Abstract: Redirection of precipitation by a crop canopy significantly affects the distribution of water entering soil. This knowledge can be used to improve crop management practices for protecting ground water. Over a 4 y period, rain and/or irrigation water was collected at 8 equidistant positions between corn (Zea Mays L.) rows. Soil water status was measured to a 0.3 m mdepth in the same relative positions. Wind direction and speed, and crop canopy development influenced the location where throughfall entered the soil surface and resultant soil water content. Stemflow increased to greater than 60 percent of incoming precipitation with canopy closure in most years. These large amounts of water entering the soil as stemflow increased percolation in the row and soil water content below the row, the zone of greatest depletion of plant available water. Associated with canopy closure, reduced throughfall reached the soil surface within 0.2 m of the row; hence, a reduced potential for leaching of agrichemicals applied in this area.