Maximize corn production with good surface and internal drainage.
By Phil Tacker, Earl Vories and Gary Huitink
Adequate drainage is necessary for maximum corn production. Poor drainage hampers field operations from field preparation through harvest and limits the effectiveness of irrigation. Eliminating poorly drained areas preserves natural soil productivity by reducing field rutting that requires additional tillage. Poorly drained areas reduce yields and often require the most tillage. Water infiltration is also reduced if soil is tilled when it is too wet.
Good field drainage complements all crop production practices and makes it possible to consider reduced or no-till corn production. The goal for drainage is to have minimal standing water on a field 24 hours after a rainfall or irrigation.
Improve Surface Drainage
Field surface smoothing and forming, prior to bedding, can improve the surface drainage of a field. Use land planes to smooth out the high spots and fill in the low areas so that the field has a more uniform slope toward drainage outlets. Low areas that are larger than 100 feet across or that require more than six inches of fill should be overfilled and compacted before being planed.
Make an effort to accurately determine a field’s drainage flow pattern. Deciding where water will drain by simply looking at the field is not always easy. Some limited surveying of field elevations can be very helpful in determining where to place tail water furrows and field drain outlets.
Precision grading of a field provides a positive method of improving surface drainage as well as making furrow irrigation possible. If a field is being considered for precision grading, the soil should be evaluated to determine what problems might occur if deep cuts are made in some areas. The cut areas may expose soil with reduced production capability. County soil survey reports, published by the Natural Resources Conservation Service (NRCS, formerly SCS), can help identify soils with unproductive subsoils. Taking several deep (more than six-inch depth) soil cores or samples may be beneficial if a problem soil is suspected. Poultry litter application may improve the productivity of cut soils.
Important Precision Grading Recommendations
Precision grading is limited to fields with slopes of less than one percent or the cost can be prohibitive. If possible, the finished grade in the primary slope direction should range from 0.1 to 0.5 percent (% 0.1 to 0.5 ft. per 100 ft.). This range provides good surface drainage without increasing erosion potential. Slopes of less than 0.1 percent are suitable for cross slopes but should be limited to slope lengths of a quarter mile or less. Slopes less than 0.1 percent are more difficult to construct with precision, and they tend to develop more low areas and reverse grades.
It is also recommended to consider putting a field to grade in only one direction (i.e., zero cross slope) if it doesn’t require a signi-ficant amount of extra cost. Building a permanent pad or elevated road on one or more sides of a field should also be considered in the grading plan. Settling often occurs in deeper fill areas and should be “touched up” before bedding if possible. The land grading design should consider the type of drain outlets and the number required for the field. If possible, it is best to provide an outlet point for every 20 acres.
An elevation survey of the field is required before any design work can be done. Survey information can be entered into a computer program that evaluates possible drainage options for a field and determines the cuts and fills required. Most land grading contractors offer the computer program design, and it is sometimes available through the NRCS.
The lowest expected elevation of the field should be determined before grading begins to assure that water will drain into the surrounding ditches adequately and not back up onto the field. It may be necessary to divide the field into shorter segments to ensure that the runoff leaves the field.
Precision grading is usually expensive and is a long-term investment for increasing production efficiency and potential and the market value of the land. Government funded conservation programs sometimes offer cost sharing on precision grading and/or other conservation best management practices. Information on these programs can be obtained through NRCS.
Constructing Drain Furrows
Good surface drainage is even more important if corn is planted flat rather than on raised rows or beds. Low areas in a flat-planted field are likely to have poor production for obvious reasons. Drain furrows to these areas can be used to reduce the effect on the crop.
Shallow and narrow drain furrows can be constructed with several different types of equipment. The equipment should spread the soil evenly away from the drain furrow, so flow into the furrow is not restricted. Construct drain furrows in the low areas of a field rather than putting them in randomly. They should generally run with or at a slight angle to the natural slope of the field but not across the direction of the slope.
Furrows should have continuous positive grade to assure that the water will be directed off the field. A drain furrow is not complete until it is connected to a ditch or pipe of adequate size to carry excess water away from the field.
Maintain Drainage Ditches
An important component of field drainage is the ditch system that receives the excess water and carries it away from the field. Flow restrictions in these ditches can cause excess water to remain on a field.
Drainage ditches should be maintained and routinely cleaned out to effectively handle the drainage water from a field. No-till or reduced tillage limits the sediment leaving fields and minimizes the sedimentation that occurs in drainage ditches. Check ditch outlets and drainage structures to make sure that they are functioning properly and are not becoming restricted.
Planned drainage improvements could impact areas classified as wetlands. If this possibility exists, contact the local NRCS staff to see what help they can provide. Typically, they can visit the site and determine if there are drainage restrictions.
Maintaining crop residue reduces surface sealing and crusting so water moves into the soil more freely.
Naturally occurring restrictive soil layers and those formed by tillage equipment restrict internal soil drainage. Shattering these layers prior to planting a corn crop is recommended to improve plant root development and internal drainage.
The restrictive layer must be dry enough for the deep tillage implement to extend just below the bottom of the restrictive layer so it is effectively lifted and shattered. If the restrictive layer begins at eight inches and is two to three inches thick, the tillage shank must penetrate 10 to 12 inches deep.
In-row subsoiling is more effective than random subsoiling paths due to the re-compaction caused by subsequent trips of the implement used.
High-residue subsoilers or ripper-hippers are suggested for maintaining the same row location year to year. Surface till-age, especially disking, reforms restrictive layers and should be avoided, if possible.
Phil Taker is a University of Arkansas Extension engineer. Contact him at (501) 671-2245 or email@example.com.