Crop residue inputs in the US Corn Belt have reached unprecedented levels. Historically, crop residue
retention was important to maintain soil organic matter and reduce erosion. However, at current levels
of residue production, partial residue harvest can improve productivity, profitability and environmental
performance. Since 1960, Iowa corn yields have increased at a rate of ~2 bushels/acre/year and Iowa
soybean yields have increased by ~0.5 bushels/acre/year. Because the production of grain and non-grain
portions of the plant have increased in tandem, residue production has increased at approximately 100
and 38 lbs dry matter/acre/year for corn and soybeans, respectively. As a result, harvest of 1/3 of current
corn residue levels would leave more residue on the field than was produced in crop year 1985.
Corn and soybean residue harvest can increase yield and N use efficiency of the following corn crop
(bushels/pound of N) without reducing soil organic matter levels. However, research about residue
harvest is piecemeal and results are inconsistent. In poorly drained soils of the northern Corn Belt, residue
harvest in corn following corn appears to consistently increase the yield of the following corn crop and
reduce the optimum N fertilizer rate. Similarly, soybean residue harvest in this region can increase N use
efficiency of the following corn crop (lbs N/bushel). However, in the drier western Corn Belt, residue
harvest appears to be detrimental to the following crop.
Residue harvest can also decrease environmental N losses. A multi-site study from Pennsylvania to
Nebraska found that, on average, corn residue harvest reduced nitrous oxide emissions by 6%. In the
wettest sites, the reduction was 17%. Although no study to our knowledge has measured the effect of
residue harvest on nitrate leaching, residue harvest consistently increases evapotranspiration, which is
known to reduce drainage and nitrate leaching.
These benefits may occur without reducing soil organic matter. A study performed across four Iowa
locations indicates that carbon inputs of approximately 2.8 tons dry matter/acre are sufficient to maintain
soil carbon stocks. Most Iowa corn and soybean cropping systems are producing much more residue.

In this proposal, we will test the following hypotheses through literature review and process modeling:
i) Residue harvest in continuous corn systems in the US Corn Belt can increase grain yield, reduce
the N fertilizer input required to achieve that grain yield, and reduce environmental N losses to
nitrate and nitrous oxide.
ii) Soybean residue harvest in corn-soybean rotation can increase corn grain yield, reduce the N
fertilizer input required to achieve that grain yield, and reduce N losses to nitrate and nitrous
oxide. These potential benefits will be most likely to occur in systems with reduced tillage and
cover crops.

To test these hypotheses, we will perform a meta-analysis based on published data from field
experiments that measure corn yield and the agronomic optimum N rate across different levels of crop
residue harvest. Specifically, we will search the peer-reviewed scientific literature for research that has
examined the effect of crop residue harvest on grain yield, N fertilizer requirements, and environmental
N losses in the following crop. Our search will encompass the northern Corn Belt (PA to NE) and Canada.
In addition, we will provide a brief review and summary of literature from other regions of the world to
provide context for our hypotheses and a need for further research about these questions in the United
States. Although work in other regions of the world has explored similar questions, the cropping systems
are considerably different with respect to crop rotation, crop genetics, soil type, soil management, and
drainage infrastructure. Hence, we cannot assume that results from these studies are transferable to
corn and soybean production systems. Importantly, we note that a likely outcome is that there is not
enough published literature for a thorough quantitative assessment in the northern Corn Belt.

To further assess the impact of corn and soybean residue harvest on environmental variables, such as
nitrous oxide emissions, nitrate leaching, and soil organic carbon change, we will use the Agricultural
Production Systems Simulator model (APSIM) that has been previously evaluated with field-measured
data across 15 sites in four states of the Corn Belt (Fig. 1). For continuous corn, we will simulate a corn
crop following i) business-as-usual management including local practices and, ii) a combination of three
different levels of residue removal and five different N fertilizer rates. We will perform the simulations
for 30 years (period 1990-2020) to account for the weather variability of the region. For corn-soybean
rotation, we will simulate the effect of two soybean residue levels (0 and 90% removal) on the optimum
N rate for the following corn crop. We will integrate these scenarios with cover crops and reduced tillage
to mitigate the effect of soybean residue harvest on erosion and soil organic carbon loss. We will
calibrate the model with soybean residue harvest data from our current experiments in Ames and a study published in the 1990s from Wisconsin. In addition, we will leverage studies from the Iowa N
Initiative to collect additional data from corn following soybean with soybean residue harvest.

The above meta-analysis and modeling work will lead to two primary products: a publicly available
report as soon as the work is completed and later a peer-reviewed publication. The report and
publication will blend results from the meta-analysis with the results from the process modeling work to
identify consistencies and inconsistencies. This work will be conducted through Iowa State University
and pay the salary and benefits of a post-doctoral researcher.

Updated July 25, 2024:
In this reporting period, we summarized published literature about the effects of crop residue harvest on yield of the following crop. In total, we identified 711 cases including 231 pairs of yield data for medium residue harvest and 221 pairs for high residue harvest (each pair compares yield in side-by-side plots with and without the residue harvest). All cases are from the US Corn Belt. Of these data, 576 pairs are from 2000-present including 226 from medium and 156 pairs for high residue harvest. We have created a database housing these data.

In addition, we have summarized published literature about the effects crop residue harvest on environmental performance. We found no articles that investigate the effect of crop residue harvest on nitrate leaching, despite significant scientific evidence that suggests medium and high crop residue harvest should reduce nitrate leaching by increasing evapotranspiration (the amount of water leaving tiles drains is the main driver of nitrate loss; hence an increase in evapotranspiration should reduce nitrate leaching). However, we identified 26 and 60 pairs of data for nitrous oxide emissions with medium and high residue harvest. This more than doubles the previous data available. Finally, we identified four studies that report the effects of residue harvest on optimum nitrogen fertilizer rate to corn. These data include both soybean and corn residue harvest. Unfortunately, these data are insufficient to make a formal statistical analysis.

Harvesting 50% of corn residue increased the following corn yield by 3.3% while harvesting maximum corn residue (close to 100%) increased the following corn yield by 4.7%. Harvesting 50% of corn residue reduced nitrous oxide emissions by 8.3% while harvesting maximum corn residue reduced nitrous oxide emissions by 11.6%.
A major conclusion of our work to date is that few studies have examined the effect of soybean residue on corn yield and environmental performance despite some suggestions that soybean residue harvest can benefit corn yield. Importantly, there is a total lack of ‘systems’ level work that aims to design an optimum residue management system. For example, soybean residue harvest paired with reduced tillage (a reduction in tillage would avoid the erosion concern of harvesting soybean residue). A similar systems design question might be to manage nitrogen differently with and without residue harvest given that the little available literature suggests partial residue harvest reduces nitrogen fertilizer needs.

Updated January 26, 2025:
This project addressed two questions about the implications of increasing crop residue production in the northern US Corn Belt: i) How does crop residue amount, and crop residue harvest affect crop yield and environmental N losses in maize and soybean systems? and ii) How does maize residue harvest affect life-cycle greenhouse gas emissions from continuous maize systems? To answer these questions we applied three different approaches. First, we performed a meta-analysis based on published data of maize and soybean yield and nitrous oxide emissions under residue harvesting management in the US Corn Belt. Then, using a simulation model we estimated the effect of residue harvesting on crop yield, N2O emissions and NO3- leaching for different amounts of residue harvested. Finally, we calculated the carbon intensity of maize production through a Life-Cycle-Assessment. As an integrative step, we develop a systems-level rethinking of crop production that pairs partial residue harvest with no-till practices to benefit productivity and environmental performance as an alternative to the current management based on intense tillage.
The effect of residue harvesting on the following crop yield changed over time. Before the year 2000, harvesting the residue reduced the crop yield in the following year. Following the current trend of increasing yield with time, the effect of harvesting the residue turned out to be positive post-2000.
Modern experiments (from year 2000 to present) show that harvesting maize residue:
1. increases the following maize yield by 3.7% in a maize-maize sequence
2. increases soybean yield by 3.6% in the 2-year maize-soybean rotation
There was only sufficient data to investigate the effects of maize residue harvest on the following maize yield and N2O emissions for continuous maize systems. In this case, the effect of maize residue harvesting on the following maize crop yield and N2O emissions differed with tillage systems. In conventional tillage systems, residue harvest had no significant effect on the following maize yield and N2O emissions. On the contrary, under no-till system, harvesting the maize residue increased the following maize yield by 6.2% and reduced the N2O emissions by 20%.
Finally, when comparing our new proposed management system including partial residue harvesting under no-till system vs. the current management with no residue harvesting under conventional tillage, there was no effect on yield, but the N2O emission was reduced by 33%. Hence, harvesting residue eliminated the yield penalty associated with no-tillage. In other words, continuous maize with no-tillage generally yield 5% less than continuous maize with tillage; yet there was no yield difference in continuous maize with conventional tillage and residue harvest vs. continuous maize with no-tillage and partial residue harvest.
Using the APSIM cropping systems process model in different site across the 5 main states in the Corn Belt (IN, IL, IA, MN and NE) we found that each metric ton of maize residue harvested per hectare increased the subsequent maize yields by an average of 246 kg ha-1 while reducing N2O emissions and NO3- leaching by an average of 0.180 and 0.932 kg N ha-1 (12 metric tons maize yield per ha = 192 bushels per acre). Based on the Life-Cycle-Assessment, improved systems (partial residue harvesting + no-till) increased diesel fuel use by 12.16 L ha-1, which represents a 10% increase in the carbon intensity. However, the N2O emissions reduction under this scenario represented a carbon intensity 16% lower than BAU management.

This research explored the effects of harvesting part of maize residues on yield and nitrous oxide emissions in corn following corn and corn-soybean rotations. We used a meta-analysis of field-measured data and simulations across the northern Corn Belt. The simulation data also allowed us to explore the effects of maize residue harvest on nitrate leaching.
In the meta-analysis of field-measured data, harvesting maize residue increased the following maize yield by 3.7% on average across all data. However, under conventional tillage there was no effect of residue harvest while residue harvest under no-tillage increased following corn yields by 6.2% and soybean yield by 3.6%. Hence, corn residue harvest eliminated the yield penalty associated with no-tillage.
The benefits of residue harvest on the following corn yield increase with higher yields and residue prodution. While in the past (1980-2000) residue harvest had a negative impact on yield, the effect from 2000-present was significantly positive.
A switch from continuous corn with conventional tillage and no residue harvest to continuous corn with residue harvest had no effect on corn yield and reduced N2O emissions by ~30%, representing a major reduction in carbon intensity score of corn production.
The benefits on yield reported here are conservative since residue harvesting can warm and dry the soil in spring and allow earlier plating, which has been shown to increase soybean yield and further reduce N2O emissions.
Model simulations indicate significant reductions in nitrate leaching with residue harvest (~30%) owing to greater evapotranspiration.
Our estimates suggest that, conservatively, residue harvest can reduce the carbon intensity score of corn by >15%.
As yields increase, residue production increases. There is a critical need to understand how residue harvest affects soybean yield and enables conservation practices such as no-tillage and cover crops. Residue harvest should improve the performance of both practices while increasing crop yields and reducing environmental nitrogen losses, but there is little data available for the corn-soybean system.

i) determine the combinations genetics, environment, and management that are mostly likely to
achieve, and maximize, the results described above;
ii) prompt the Department of Energy to reduce the carbon intensity score of biofuels owing to
reductions in N fertilizer and nitrous oxide associated with residue harvest;
iii) demonstrate the world-leading efficiency of Iowa crop production to grain purchasers and other
organizations with an interest in environmental outcomes.