Relay cropping offers economic benefits and reduces nitrate leaching from soils
—Reproduced from the September 19, 2003 issue of CropWatch
Producers are continuously fine-tuning their production practices, seeking ways to use labor and capital more efficiently and increase profits while protecting the environment. This includes making better and more efficient purchasing decisions and developing improved marketing strategies to create more profit from their farming operation.
Relay cropping is essentially a special version of double cropping, where the second crop is planted into the first crop before harvest, rather than waiting until after harvest as in true double-cropping. In this way, both crops share a portion of the growing season, increasing solar radiation and heat available to each.
Wheat is harvested with little disturbance to the growing soybean crop.
Two 10-inch rows of wheat were planted between two rows of seed corn planted on 30-inch centers. Wheat was seeded between the corn rows in late September after the seed corn was harvested. The beans were seeded in late May on top of the old corn rows (thus in 30-inch rows). A tractor with narrow tracks was used to seed soybeans, and the wheat was cut about knee high to avoid clipping off the tops of the beans. The 20-inch spaces between the wheat rows where the soybeans were planted allowed more sunlight to penetrate to the beans and the narrow tracks didn’t disrupt the wheat canopy.
The rotation of corn grown for seed and soybean seems to be well suited to relay cropping because seed corn is harvested in mid-September (earlier than full-season field corn) and the remaining residue is not excessive. A winter annual crop, such as winter wheat, could be inserted into the seed corn-soybean rotation to use the solar energy and heat units available between corn harvest in September and soybean planting in May. However, winter wheat is not harvested until mid-July -- far after the optimum time to plant soybean.
Hence the need to relay crop the winter wheat and soybean in this seed corn-winter wheat-soybean crop sequence. For successful relay cropping, several things would usually be necessary in Nebraska: center-pivot irrigation, glyphosate-tolerant soybeans, and a means of seeding soybeans into wheat at heading (about 30 days before wheat harvest).
System pros and cons
Relay cropping has advantages and disadvantages compared to standard cropping practices. Advantages include
- the potential to reduce nitrate leaching (wheat acts as a scavenger crop),
- increase carbon sequestration,
- and increase income for producers.
Unfortunately, a relay system is not without risk. Disadvantages:
- The soybean planting process will likely stress the wheat crop and reduce yield from what would be expected of a non-disturbed crop.
- Likewise, wheat harvest may stress the soybean crop.
The hope is that the two crops will result in greater income (and profit) than either single crop grown without disturbance.
- Relay cropping requires a greater level of management. Wheat must be planted during the soybean and corn harvest season and planting soybean into a standing crop is a new process to most farmers.
- Also, pest management and control practices must account for more crops being grown in close sequence. The system may not allow time for herbicide carry-over levels to decline and may increase the potential for insect and disease infestations if these pests have more than one host in the crop sequence.
Current relay cropping research
A team of USDA-ARS researchers at the University of Nebraska-Lincoln is conducting a relay cropping trial in cooperation with several producers in south central Nebraska. This evaluation was started in 2002 with 150 acres in cooperation with one farmer, and was expanded to about 1,500 acres with four cooperating farmers in 2003.
First year results with the seed corn-wheat-soybean rotation showed that the wheat crop yielded 68 bushels per acre and removed 130 lb nitrogen per acre from the soil (about 90 lb nitrogen per acre in grain) that could have leached beneath the root zone. The wheat produced about 2 tons of residue per acre, which will help build soil organic matter content and control erosion. In addition, profit increased by about $100 per acre. This was even after accounting for a 15% reduction in soybean yields (which averaged 55 bushels per acre).
Wheat yields in 2003 ranged from 55 to 75 bushels per acre. In many areas, the yield monitor showed yields may have exceeded 90 bushels per acre.
Producers observed that the isolation areas around the perimeter of seed fields (about 90 feet wide) sometimes yielded up to 20% more than in the bulk field where seed corn was previously grown. These isolation areas were planted to wheat, soybean, or sorghum the previous year. Reasons for greater wheat yields in the border areas are unknown, but could hold the key to enhanced production and profitability from relay -cropping.
Possible explanations may include
- herbicide carryover after seed corn,
- nitrogen immobilization by the corn residue,
- seedbed and planting differences,
- different levels of residual nitrogen (nitrate-N) in the bulk field compared with the border area,
- and disease interactions.
Producers noted that plants in the border areas were more vigorous in the early growth stages and more erect at harvest.
Table 1. N, P, and K removal in grain of corn, soybean, and wheat all at 60 bu/acre yield.
Judicious nutrient management is critical to help reduce environmental effects of excess crop nutrients in the soil and maximize profit. Nutrient management is an important component of the relay cropping system.
Each crop has different requirements although it may not be convenient or economical to apply nutrients to each crop. Excess nitrate can leach into groundwater while phosphorus can be carried in runoff to surface water where excess levels can enhance algae growth, and in turn reduce oxygen for fish and other aquatic organisms.
For the same yield level (60 bushels per acre), each crop removes a different amount of each nutrient in grain (Table 1).
- Soybean removes the greatest amounts of all three nutrients since concentrations of nitrogen, phosphorus, and potassium are much greater than with the other crops (Table 2).
- Nitrogen, phosphorus and potassium applications are recommended when the soil test levels fall below the critical level (Table 3).
- Potassium is usually very high in Nebraska soils and only a few soils would require more. Nitrogen is not normally applied to soybean.
- All three crops would require adding phosphorus if the soil test level falls below the critical level. The recommended amount of phosphorus applied for each crop is lower than the crop removal since soil provides some of the phosphorus needed for each crop.
It may be possible to use short-season corn hybrids instead of seed corn in this relay cropping system. The challenge is to harvest corn early enough (by mid-September) to allow timely planting of wheat or similar winter annual crops.
Other challenges of using corn hybrids include residue management, the mechanics of planting wheat into the large quantity of residue produced by hybrid corn, and the possibility that short-season hybrids would produce less grain than full season hybrids, complicating the economics of the relay system.
Winter cover crop after soybean
Soybean fields typically lay idle after harvest until corn is planted in mid to late April. This could be an opportune time to grow a winter cover crop if there are economic or environmental reasons to do so.
Soybean is a good scavenger crop for residual soil nitrogen, so the risk of nitrate leaching would probably not provide a strong environmental incentive; however, a winter cover crop would protect soil susceptible to erosion with the limited residue remaining after a soybean crop.
Producers with livestock might find the production of triticale (a cross between wheat and rye) a worthwhile alternative for grazing or green-chop.
The USDA-ARS team is conducting further studies on various components of the relay cropping system. In one study at the Management System Evaluation Area (MSEA) site southwest of Shelton, they are evaluating the yield potential of short season hybrids. Use of short-season hybrids may allow producers without seed corn contracts to try the corn-winter wheat-soybean relay cropping system by permitting timely planting of the winter annual crop. Another study was initiated to assess the ramifications of terminating full-season corn hybrid growth before physiological maturity with glyphosate to allow early harvest so that a cover crop can be planted earlier and again permit timely planting of the winter annual crop.
Producers cooperating in the relay cropping research project this year are:
- Paul Gangwish, Shelton
- Curtis Rohrich, Wood River
- David Brown, Wood River
- Gary Urwiller, Ravenna
Scientists from the USDA-ARS working on this project, their areas of specialty, and how to contact them:
- Dennis Francis, general information and crop sensors; 113 Keim Hall, Lincoln, NE 68583; (402) 472-8494; email: email@example.com
- John Shanahan, crop stress detection; 110 Keim Hall, Lincoln, NE 68583; (402) 472-1511; email: firstname.lastname@example.org