Managing the Continuous Corn Yield Penalty
with Crop Management

Highlights

As one of the Seven Wonders of the Corn Yield World, previous crop plays a vital role in maximizing corn grain yields. While many aspects contribute to a farmer’s decision to alter corn or soybean acres in Illinois, continuous corn still constitutes over 20% of corn acres despite the wide acknowledgement of a yield penalty (Figure 1). Previous research conducted by the Crop Physiology Laboratory indicated that the primary agents of yield reduction in continuous corn were nitrogen availability, residue accumulation, and the weather (Gentry et al., 2013). Our current research was designed to determine how to reduce or eliminate these causative factors, and we focused on the effects of enhanced fertility and agronomic management, and hybrid selection for increased corn yields and reduced continuous corn yield penalties (CCYP).

Introduction

After three consecutive years of disappointing yields in the Corn Belt (2011-13), farmer enthusiasm for continuous corn (CC) began to wane. Escalating corn prices have encouraged many farmers to attempt growing corn continuously (3 or more years) or to move to a corn-corn-soybean rotation as opposed to the traditional corn-soybean (CS) rotation. Although corn can be cropped continuously, it is widely accepted that there is a yield reduction compared to corn rotated with soybean. We refer to the corn yield difference for CC and CS systems as the continuous corn yield penalty (CCYP). Although it varies, the CCYP is generally in the range of 20 to 30 bushels per acre. Despite many years of agronomic research, the cause(s) for the CCYP remains unclear. A common belief among growers, however, is that the CCYP “goes away” over time, so that after 4-6 years of CC, yields increase to the same level as corn following soybean.

Does Intensive Management Alleviate the Continuous Corn Yield Penalty?

The yield penalty associated with 11^th year continuous corn vs. long-term corn following soybean grown was assessed using either a standard or a high input management system during the 2014 and 2015 growing seasons in Urbana, IL (Figures 2 and 3). In each year the CCYP was evaluated using eight commercially-available hybrids that display a range of tolerance to fields planted to continuously grown corn (2014 Monsanto hybrids; 2015 Winfield Croplan hybrids). Factors in our management systems included nitrogen, phosphorus, potassium, fungicide, and population. The standard management system, designed to emulate the typical grower’s management practices, consisted of a base rate of nitrogen fertilizer (180 lbs N acre^-1), no additional fertility, and no fungicide application, and planted to obtain an approximate final density of 32,000 plants acre^-1. The intensive management system (i.e., high input) was planted to obtain an approximate final stand of 45,000 plants acre^-1 with banded fertility 4 to 6 inches directly beneath the crop row preplant to provide enhanced P (100 lbs P₂O₅ acre^-1), S (25 lbs acre^-1), and Zn (2.5 lbs acre^-1) nutrition (supplied as Mosaic’s MicroEssentials-SZ; 12-40-0-10S-1Zn), and broadcast fertility just prior to planting to provide enhanced K (75 lbs K₂O acre^-1) and B (0.4 lbs B acre^-1) (supplied as Mosaic’s Aspire; 0-0-58-0.5B). The intensive management system also received an additional 60 lbs N acre^-1 sidedress application stabilized with a urease inhibitor (BASF’s Limus) at crop growth stage V5, and protected with a foliar fungicide application (14.4 oz acre^-1 BASF’s Headline AMP) at Vt/R1.

Intensive Management for Continuous Corn

The yield penalty associated with 11th year CC vs. long- term CS rotation was assessed using either a standard or an intensive management system, with contrasting plant populations (32,000 and 45,000 plants/acre), and eight commercially available hybrids with distinctly different genetic makeups.

The standard management system consisted of:

a base rate of nitrogen fertilizer (180 lb N /acre),
no additional fertility
no fungicide application
32,000 plants/ acre

The intensive management system consisted of:

Additional sidedressed nitrogen fertilizer (60 lb N/ acre with a urease inhibitor),
Phosphorus, Sulfur and Zn fertility banded 4-6 inches directly beneath the crop row preplant to provide 100 lb P₂O5₅/acre, 25 lb S/acre, and 2.5 lbs Zn/acre (supplied as Mosaic’s Microessentials SZ: 12-40-0-10S-1Zn)
K and B fertility broadcast just prior to to planting to provide 75 lb K2O/ acre and 0.4 lb B/ acre (supplied as Mosaic’s Aspire: 0-0-58-0.5B)
Sidedress 60 lbs N/ acre BASF’s Limus (Urea with urease inhiitor) at V5
Foliar fungicide application at growth stage VT/R1 (silking) of 14.4 oz/ acre BASF’s Headline AMP
45,000 plants/ acre

Results

Intensive management increased yield in continuous corn by 50 bushels per acre, and in the CS rotation by 32 bushels per acre, suggesting intensive management as a way to mitigate the continuous corn yield penalty.

Table 1.  Effect of management level and rotation on final grain yield in continuous corn (11^th year; CC) and following soybean (CS) rotations at Urbana, IL in 2014 and 2015. Values are the average of eight hybrids and are presented as 15.5% moisture (2014-Monsanto hybrids; 2015-Croplan hybrids). The continuous corn yield penalty (CCYP) is the yield difference between 1^st year corn in a corn-soybean rotation and 11^th year continuously grown corn.

Visual differences in plant appearance between continuous corn and rotated corn were readily apparent; starting from the ground up, continuous corn had corn residue accumulation with firing and yellowing of leaves on the plant compared to 1^st year corn in a corn-soybean rotation where there was no or minimal firing or yellowing of the leaves (Figure 2). Across treatments, grain yield of continuous corn was reduced by 13% and 21% in 2014 and 2015, respectively (Table 1). The overall magnitude of the CCYP varied by growing environment and hybrids grown within a year (-29 bu acre^-1 in 2014 and -48 bu acre^-1 in 2015 averaged across treatments).

Does Hybrid Selection Play a Role in the CCYP?

Selecting a corn hybrid that tolerates continuously grown corn acres and responds to agronomic management is an important factor to maximize corn grain yields and manage the CCYP. We found select hybrids grown with high input management were able to reduce the CCYP by 50 to more than 100% (2014 – DKC60-67RIB, DKC64-87RIB, 209-53STXRIB, 212-86STXRIB, DKC63-55RIB; 2015 – 6110SS, 6065SS, and 6640VT3P; Tables 2, 3, 4, & 5).

Across management levels in 2014, hybrids DKC60-67RIB and 209-53STXRIB significantly out yielded the rest of the hybrids in continuous corn (LSD (P ≤ 0.1) = 9.2), while in the corn-soybean rotation hybrids DKC64-87RIB, DKC63-33RIB, and 209-53STXRIB excelled (LSD (P ≤ 0.1) = 9.6; Table 2). Averaged across management levels in 2015, 6110SS achieved the highest yield in continuous corn (LSD (P ≤ 0.1) = 27.9), and while among hybrids in the corn-soybean rotation there was no significant difference, 6594SS tended to have the greatest yields (Table 3).

Compared to Winfield’s response to continuous corn (RTCC) ratings, hybrids reflect similar responses to continuous corn in this trial. Across managements, 5415SS and 6065SS had the lowest CCYP (27 bu acre^-1 for both hybrids; RTCC = 2 and 3) while 6265SS had the highest CCYP (74 bu acre^-1; RTCC = 8; Table 5). The importance of hybrid selection is emphasized through the variability in responses by hybrid to management factors such as fertility and previous crop.

Table 2.  Effect of management level, rotation, and eight Monsanto hybrids on final grain yield in continuous corn (11^th year) and following soybean rotations at Urbana, IL in 2014. Values are presented as 15.5% moisture.

Table 3.  Effect of management level, rotation, and eight Winfield – Croplan hybrids on final grain yield in continuous corn (11^th year) and following soybean rotations at Urbana, IL in 2015. Values are presented as 15.5% moisture.

Table 4.  The yield penalty associated with continuous corn under two levels of crop management at Urbana, IL in 2014. Eight Monsanto hybrids with a range response to continuously grown corn (RTCC) were grown in continuous corn (11^th year) and following soybean rotations. Values are presented as 15.5% moisture. The continuous corn yield penalty (CCYP) is the yield difference between 1^st year corn in a corn-soybean rotation and 11^th year continuously grown corn.

Table 5.  The yield penalty associated with continuous corn under two levels of crop management at Urbana, IL in 2015. Eight Winfield hybrids with a range response to continuously grown corn (RTCC) were grown in continuous corn (11^th year) and following soybean rotations. Values are presented as 15.5% moisture. The continuous corn yield penalty (CCYP) is the yield difference between 1^st year corn in a corn-soybean rotation and 11^th year continuously grown corn. The RTCC ratings are on a scale of 1 = suitable for continuous corn to 9 = needs extra management to overcome CCYP.

Conclusions- Intensive Management The results of this work suggest a multifaceted approach to crop management, especially hybrid selection in combination with high input management practices, will continue to play an important role in managing the CCYP and increasing corn yields. Intensified management (i.e., high input) increased yields regardless of cropping system and significantly reduced the CCYP. In addition, select hybrids with enhanced management (i.e., additional fertility and a foliar fungicide application) reduced the CCYP by 50% to >100%, suggesting the importance of these management factors in maximizing productivity of continuously grown corn. Although the CCYP could be significantly reduced by high input management and hybrid selection, the yield penalty still existed despite growing seasons that were near-perfect, presumably stress-free weather conditions.  

Next Step: Corn Residue Management to Lessen the CCYP

Previous work by our laboratory has indicated that the primary agents of yield reduction in continuous corn are nitrogen availability, residue accumulation, and weather; and that the magnitude of the penalty increases with successive years of continuous corn production due to the cumulative accumulation of residue. Through the current research we have shown that the continuous corn yield penalty can be lessened with better fertility, foliar protection, and proper hybrid selection, and we will extend that research to evaluate residue management. A variety of techniques designed to manage the previous crop’s residue (mechanical and chemical), will be combined with agronomic management systems (standard or high input), and with hybrid selection (tolerant or non-tolerant to continuous corn) in order to further lessen or potentially eliminate the yield penalty associated with continuous corn production (Table 6; Figure 4).

For the mechanical residue management treatments, the previous year’s corn crop will be harvested with a combine head equipped with Calmer BT Chopper® stalk rollers, or with a combine head equipped with standard knife rollers. Both the chopped and standard harvested residue treatments will be further managed chemically by applying either Extract Powered by Accomplish^TM, or ammonium sulfate, and compared to an untreated control. The chemical treatments will be surface applied directly on the crop residue in the fall immediately after crop harvest.  Extract Powered by Accomplish^TM at the labeled rate will be mixed with one gallon of 28% liquid UAN (urea/ammonium nitrate) and sprayed onto the soil surface, while granular ammonium sulfate will be broadcast on the soil surface at a rate 200 lbs of ammonium sulfate per acre (42 lbs of N per acre). The first year corn treatment, where soybean was the previous crop, will only receive the chemical residue treatments. The mechanical and chemical residue management treatments being investigated are designed to help growers manage crop residue by increasing decomposition rate and release of nutrients from that residue for plant uptake.

The agronomic management systems (standard or high input) mentioned previously in the research approach will remain the same and two commercial corn hybrids selected for differences in their tolerance to continuous corn in our previous work will be grown in each management system.

Table 6.  Proposed treatments to be implemented in 13^th year continuous corn and 1^st year corn in a corn-soybean rotation at Urbana, IL during 2016 and 2017.

Figure 4.  Visual comparison of mechanical residue management treatments in Urbana, IL during harvest 2015 of continuous corn and 1^st year corn following soybean. A plot harvested with a combine head equipped with standard knife rollers (left) vs. a plot harvested with a combine head equipped with Calmer BT Chopper^® stalk rollers (right).

Related documents and links

Gentry, L.F., M.L. Ruffo, and F.E. Below. 2013. Identifying factors controlling the continuous corn yield penalty. Agron. J. 105: 295-303. [open access .pdf]

Vogel, A.M., and F.E. Below. 2017. Mitigating the continuous corn yield penalty with residue and agronomic management. (abstract #230-6). Presented at the International ASA-CSSA-SSSA meetings, Oct. 22-25, Tampa, FL (poster .pdf)

Vogel, A. M. 2017. Knocking out the continuous corn yield penalty. Proceedings of the University of Illinois Agronomy Day, Aug. 17, 2017. Urbana, IL. .pdf

Vogel, A.M., T.A. Beyrer, and F.E. Below. 2016. Residue and agronomic management to lessen the continuous corn yield penalty. (abstract # 102097). Presented at the International ASA-CSSA-SSSA meetings, Nov. 6-9, Phoenix, AZ (poster .pdf)

Vogel, A., Gentry, L.F., and F.E. Below. 2015. Alleviating the Continuous Corn yield Penalty with Crop Management. University of Illinois Agronomy Day. Aug. 24, 2015. [.pdf]

Vogel, A.M. L.F. Gentry, R.R. Bender, and F.E. Below. 2015. Better fertility and agronomic management helps to lessen the continuous corn yield penalty. Proceedings of the Fluid Fertilizer Forum Feb. 17, 2015, Scottsdale, AZ. .pdf