Wheat Underseeded with Red Clover Maximizes Corn Yield

by Tony J. Vyn, Ken J. Janovicek and H. Wichers, University of Guelph

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Recent results from Ontario's long-term rotation trials have once again confirmed that corn yields are higher following wheat underseeded with red clover than they are following corn, soybeans or even wheat alone in sequence. Ontario farmer decisions to reduce and, in some cases, to completely
eliminate wheat and/or underseeded red clover from their rotations has had negative consequences for short-term profitability and long-term productivity of their soils. This article summarizes the corn yield responses to rotation observed over the past eight years on medium- and fine-textured soils.

Corn Yields After Red Clover

Highest corn yields consistently occurred following wheat which had been underseeded with red clover (Tables 1 and 2). At the Chatham and Elora locations, corn yields following wheat were higher than those following soybeans only when wheat was underseeded with red clover. In fact,
corn yields achieved following underseeded clover were similar to those observed following up to two complete growing seasons of forage legumes (alfalfa or red clover) at these locations. This indicates the corn yield benefits associated with following forage legumes in a rotation were fully
realized even when red clover is incorporated in the same year it is underseeded.

Table 1 - Corn yield response to rotation on a Toledo loam near Chatham, Kent County, and on a Brookston clay loam near Maidstone, Essex County
Rotation*	Corn Yield ( bu/ac )
	Loam (1990-95)	Clay loam (1990-93)
Continuous Corn	141	105
Soybean-Corn	156	118
SoybeanSoybean-Wheat (RC)** -Corn Wheat-Corn	151	126
Soybean-Wheat (RC)** -Corn	163	135
* All corn treatments were fertilized with 160 lbs/ac of N and fall moldboard plowed.Data courtesy of Doug Young, Ridgetown College, University of Guelph. ** Red clover plow-down was underseeded into wheat.

Underseeding wheat with red clover increased the following year corn yield by 9-12 bu/ac (seven per cent) over wheat alone at all three locationsin the moldboard system (Tables 1 and 2). Assuming that corn is sold at the 1997-98 Market Revenue price of $3.43/bu, this yield increase is
worth about $30 to $40/ac (or at least double the $15 seeding cost of red clover).

The yield benefits associated with red clover seem to persist for at least two years. For example, underseeding wheat with red clover at Elora increased second-year corn yields by nine bu/ac. The crop yield increases over three years associated with underseeding red clover one year out of four increased returns about $80/ac (assuming corn and soybeans are sold at market revenue prices).

Inclusion of wheat into a crop rotation, especially when underseeded, also increased corn yields in a fall chisel plow system (Table 2). The corn yield increases associated with underseeding red clover - relative to after wheat alone - were not as great as in the moldboard system.

Related Considerations

In addition to crop yield increases, underseeding red clover will often reduce the nitrogen fertilizer requirement for corn during the following year. Even short (e.g., up to 10-inchhigh) stands of red clover should be credited with supplying 40 lb/ac of N as long as the stand is relatively uniform.

An argument often used against underseeding red clover is the difficulty associated with consistently getting good stands. Without very good site specific maps and application equipment, it is virtually impossible to assign proper N fertilizer credits after spotty stands.

However, where red clover did establish, the crop yield increases will still occur. For example, even if red clover had only been established on half the field at the Elora site, the crop yield benefits in that area would still be worth $40/acre in a four-year rotation cycle.

Soil Structure

Planting more years of soybeans and fewer years of wheat in a rotation system will also result in a deterioration of soil structure and limit long-term soil productivity. In fact, the structure of soil in corn-soybean rotations can actually be poorer than soils in continuous corn
production.

For example, erosion following an intense June rainstorm following two years of soybeans at the Elora site was twice as high as following either continuous corn or wheat underseeded with red clover (just 1 year in 4).

Conclusions

The rotation benefit of including winter wheat is maximized when it is underseeded with red clover. Without underseeding, corn yields after wheat are 10 per cent higher than for continuous corn on loam and clay loam soils. With underseeded red clover, first-year corn yields were increased an
additional seven per cent (compared to after wheat alone) in all three experiments.

Since the soil structure and yield benefit of red clover persist well beyond the first year, and since profitability is assured even if only 50 per cent of the field has successful establishment and even if no fertilizer N credit is acknowledged, Ontario farmers should always underseed red clover into their winter wheat fields.

Table 2 - Rotation and fall tillage system effects on first- and second-year corn yields on a silt loam soil near Elora, Wellington County (1994-97)
Rotation*	Moldboard	Chisel	Moldboard	Chisel
First Year Yields
Second Year Yields
Continuous Corn bu/ac	155	142	151	141
Soybean-Soybean-Corn-Corn	159	149	145	136
Soybean-Wheat-Corn-Corn	157	158	141	142
Soybean-Wheat (RC)** -Corn-Corn	169	164	150	143
*Rotation sequences were initiated in 1980; results in this table are those after four complete four-year cycles. All corn treatments were fertilized with 150 lbs/ac of N. ** Red clover plow-down was A GOOD CROP ROTATION - YOU CAN'T FARM WITHOUT IT by Tony Vyn, Crop Science Department, University of Guelph Ontario soybean acreage exceeded corn acreage by approximately 40% in 1997. The doubling of soybean acreage in the last 10 years has resulted in dramatic shifts in crop rotation practices on Ontario farms. Many farms which 20 years ago had rotations involving 2 or more consecutive years of corn, now have rotations which contain 2 or more consecutive years of soybeans. Many cash-crop farmers have also dropped winter wheat from the 3-year rotation system of corn-soybean-wheat which was popular during the 1980's. Aside from soybean disease concerns, the two biggest risks with increasing the frequency of soybeans in crop rotations are (a) loss of soil structure and (b) limiting potential corn and soybean yields. YIELD RESPONSE TO ROTATION SYSTEMS Ontario's rotation research has clearly indicated increased corn yields when corn is rotated with other crops. Highest yields occurred when forage legumes (i.e. alfalfa or red clover) precede corn in rotation. Research conducted by Doug Young of Ridgetown College observed corn yield responses to rotation were up to 30% higher than continuous corn on medium and fine-textured soils in Southwestern Ontario (Table 1). Table 1.Corn yield response to rotation on a Toledo loam near Chatham and on a Brookston clay loam near Maidstone. Rotation       Clay loam(1990-93) bu/ac Loam (1990-1995) bu/ac Continuous Corn 105 141 Soybean-Corn 118 156 Soybean-Wheat-Corn 126 151 Soybean-Wheat(RC)+-Corn 135 163 Soybean-Wheat(RC)-RC+-Corn 132 165 *Red clover plow-down was underseeded into wheat. Wheat (RC)-RC indicates that underseeded red clover was not plowed under but harvested for seed the following year and then fall plowed. * All corn treatments were fertilized with 160 lbs/ac of N. Long-term rotation research (1980-97) by the University of Guelph near Elora has also found substantial corn yield increases when corn is rotated with other crops (Table 2). Yield responses to rotation were even higher in conservation (i.e. chisel plow) tillage systems than with traditional moldboard plowing on this Maryhill silt loam soil. Table 2.Rotation and fall tillage system effects on first- and second-year corn yields at Elora (1994-97). RotationMoldboard PlowChisel Plow Rotation Moldboard Plow Chisel Plow   First Year Second Year First Year Second Year Continuous Corn 155 151 142 141 Soybean-Soybean-Corn-Corn 159 145 149 136 Soybean-Wheat-Corn-Corn 157 141 158 142 Soybean-Wheat(RC)+-Corn-Corn 169 150 164 143 Alfalfa-Alfalfa-Corn-Corn 162 155 167 144 *Red clover plow-down was underseeded into wheat. *All corn treatments were fertilized with 150 lbs/ac of N. These three sites demonstrated that first-year corn yields after wheat averaged about 10% higher than those with continuous corn. Corn yields were increased an additional 7% when the wheat was underseeded with red clover. In fact, red clover plow-down resulted in corn yields which were similar to those obtained after (a) keeping the red clover for an extra year to harvest as a seed crop (Table 1) or (b) 2 years of alfalfa (Table 2). The benefits of including wheat, and especially wheat plus red clover, may persist beyond just the following year. For example, underseeding red clover into wheat at Elora resulted in second-year grain corn yield increases in the moldboard system which were almost as large as those observed for first-year corn. In addition, soybean yields during the third year after underseeding red clover were also higher than when red clover is not included in 4-year rotation systems (Table 3). Table 3.Soybean yield response to rotation on a Maryhill silt-loam soil near Elora (average of 1994 and 1996). Rotation Soybean Yield bu/ac   Moldboard Chisel Soybean-Soybean-Corn-Corn 39.5 39.4 Soybean-Wheat-Corn-Corn 38.9 42.3 Soybean-Wheat(RC)+-Corn-Corn 40.3 43.1 *Red clover plow-down was underseeded into wheat. We conclude that larger corn yield increases can be expected when rotations include winter cereals rather than just corn and soybeans, especially when the cereal is underseeded with red clover. SOIL STRUCTURE Planting more and more soybeans is increasing the susceptibility of Ontario's soils to erosion. In fact, the structure of soils in corn-soybean rotations can actually be poorer than soils which are in continuous corn production. For example, erosion following an intense June rainstorm in first-year corn following 2 years of soybeans was twice as high as following corn, wheat underseeded with red clover or alfalfa (Table 4). The increased erosion following soybeans occurred in both tillage systems. Relatively poor soil structure after 2 years of soybeans not only increased erosion susceptibility, but also reduced soil porosity which resulted in less rain water infiltration. Reduced rain-water infiltration increases the likelihood of erosion risk, yield reducing water ponding and/or soil moisture deficits; all of these effects can reduce crop productivity, particularly in years with weather-related stress. Table 4.Proportion of total rainfall which ran off, and associated soil erosion, following an intense (1.25") 10 minute rainstorm in first-year corn plots (June 1994, Elora). Rotation Moldboard Chisel   Run-off % Erosion t/ac Run-off % Erosion t/ac Continuous Corn 34 1.2 27 0.7 Soybeans-Soybeans-Corn-Corn 44 2.8 48 2.0 Soybeans-Wheat (RC)+-Corn-Corn 34 1.3 28 1.0 Alfalfa-Alfalfa-Corn-Corn 33 1.5 33 1.0 *Red clover plow-down was underseeded into wheat. ROTATION ECONOMICS EXAMPLES The economics of any rotation system are entirely dependent on assumptions made about yield levels, relative crop prices and whether crop input prices and/or timeliness of operations are affected by rotation choice. Crude (i.e. not sanctioned by economic experts) estimates of the returns for the various rotations, not accounting for land and overhead costs, are presented in Tables 5 and 6. Higher corn yields when rotated usually resulted in substantially greater returns compared to when planted continuously. Based on the assumptions presented, inclusion of wheat improved returns relative to the corn-soybean rotation everywhere but the loam site at Chatham. Table 5.Estimated annual net returns, not accounting for land and overhead costs, from rotation trials located on a Toledo loam near Chatham, Kent County and on a Brookston clay-loam near Maidstone, Essex County. Rotation Net Returns ($/acre)*   Loam Clay-loam Continuous Corn 252.20 119.00 Soybean-Corn 338.85 221.05 Soybean-Wheat-Corn 313.23 250.73 Soybean-Wheat(RC)+-Corn 323.03 256.83 *Red clover plowdown was underseeded into wheat *Return calculations based on: yields for corn from Table 1, soybean yields of 50 bu/ac on loam and 40 bu/ac on clay-loam, and wheat yields of 80 bu/ac; selling price (after drying, handling and marketing) of $3.70/bu for corn, $9.50/bu for soybeans and $5.00/bu for wheat; production costs (including seed, fertilizer, chemicals and machinery) of $241.50/ac (plus $15.00/ac for insecticide when following corn), $130.00/ac for soybeans, $119.50/ac for wheat (plus $15.00/ac if underseeded). Table 6.Estimated annual net returns, not accounting for land and overhead costs, on various 4-year rotations and continuous corn on a silt loam near Elora in a fall moldboard and chisel plow system. Rotation Net Returns ($/acre)*   Moldboard Chisel Continuous Corn 324.60 283.90 Soybean-Soybean-Corn-Corn 286.83 268.78 Soybean-Wheat-Corn-Corn 288.66 298.59 Soybean-Wheat(RC)+-Corn-Corn 307.66 303.21 *Red clover plow-down was underseeded into wheat. *Return calculations based on: yields for corn from Table 2, soybeans from Table 3, and wheat at 80 bu/ac; selling price (after drying, handling and marketing) of $3.70/bu for corn, $9.50/bu for soybeans and $5.00/bu for wheat; production costs (including seed, fertilizer, chemicals and machinery) of $226.50/ac (plus $15.00/ac for insecticide when following corn), $130.000/ac for soybeans, $119.50/ac for wheat (plus $15.00/ac if underseeded). All sites indicated that underseeding red clover enhanced profitability of the rotations relative to just wheat alone. In fact, the value of higher corn yields alone due to underseeded red clover was usually at least twice the $15.00/ac underseeding cost. For example, underseeding red clover at Chatham increased yearly per acre return of a 3-year corn-soybean-wheat rotation by $9.80/ac ($29.40/ac over the 3 years). This does not take into account the cost savings associated with reduced N requirements for corn which could be applied most years. Neither was there any income added to the wheat crop for any sale of straw. There is no doubt that profitability increases when red clover is underseeded into wheat. However, at current expected crop yields and prices there may be some questions concerning the short-term profitability of including wheat into rotations on certain well-structured soils with high yield potential. CONCLUSIONS Ontario cash crop producers should consider the loss of soil structure and productivity associated with rotations involving more and more years of soybeans. Rotations including wheat without underseeding can improve corn yields (loam to clay loam soils) by 10% relative to continuous corn and by 7% compared to alternating corn-soybean rotations on Brookston clay loam. Ontario rotation research suggests that wheat underseeded with red clover can result in considerable improvements in both soil structure and succeeding crop productivity. The benefits of wheat plus red clover can (a) be equivalent to 2 consecutive years of alfalfa and (b) may even extend well beyond the first year after incorporation. Red clover enhances profitability even if (a) it only is established successfully on half the wheat field and (b) if farmers don't give the underseeded red clover any nitrogen fertilizer credit. underseeded into wheat.

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