Capturing Sunlight: Using Row Orientation to Maximize Photosynthesis, Soil Moisture, and Weed Suppression in Cover Crop-Based Systems

Progress report for LNE23-476R

Project Type: Research Only
Funds awarded in 2023: $248,033.00
Projected End Date: 02/28/2026
Grant Recipient: University of New Hampshire
Region: Northeast
State: New Hampshire
Project Leader:
Natalie Lounsbury
University of New Hampshire
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Project Information


This project will investigate the concept of strategic manipulation of row orientation (N-S vs. E-W) to improve climate adaptation and interseeded cover crop success in silage corn and soybeans in the Northeast. Row orientation modulates the amount of sunlight that reaches the interrows and subsequently influences soil moisture and the growth of plants between crop rows (weeds or cover crops). We hypothesize that optimal row orientation will differ in non-interseeded and interseeded systems. By providing more interrow shading, E-W orientation will lead to higher soil moisture, greater weed suppression, and higher yields under most conditions in the Northeast. Conversely, by allowing more light to reach the interrow, N-S orientation will lead to greater interseeded cover crop performance without negatively affecting crop yields, which will benefit from the soil shading of the interseeded cover crop. To test these hypotheses, we will conduct research across a latitudinal and environmental gradient in Pennsylvania, New Hampshire, and Vermont. Both research station and on-farm research will investigate the effects of row orientation on crop and cover crop performance in interseeded and non-interseeded systems and will elucidate mechanisms behind the observed results, including the effects of row orientation on light, soil moisture, and weed dynamics. Cover cropping in the Northeast is rapidly expanding, but is implemented on <20% of annual crop acres in the three states where research will be conducted. Farmers have expressed interest in interseeding as a way to expand the diversity of cover crop species that can be grown in short growing seasons, but have reservations about inconsistent performance of interseeding. This project will provide critical data on how intentional row orientation can be used to reduce variability in interseeded cover crop performance, eliminating some of the barriers to adopting the practice. In addition, it will provide data on a free climate adaptive practice on acreage that is not interseeded. This makes the project unique in that it meets farmers “where they are” with respect to climate adaptation. Farmers will be engaged throughout the project with interactive field days and demonstrations, and on-farm research trials in the third year of the project. 


Project Objective:

Strategic manipulation of crop row orientation (N-S vs. E-W) holds promise as a way to enhance interseeded cover crop performance and as a standalone practice to conserve soil moisture and suppress weeds, but it has not been systematically investigated. The objective of this project is to quantify the effects of row orientation on yields, soil moisture, light, weeds, and interseeded cover crops in silage corn and soybean systems. Our research has potential to improve the reliability and therefore adoption of interseeded cover crops while also providing a climate adaptive technique on acreage where interseeding is not practiced.   


Intentionally orienting crop rows N-S or E-W is not widely recognized by farmers and researchers as a climate adaptive practice [1, 2]. This is a missed opportunity for farmers, as compelling evidence (reviewed below) suggests that strategic manipulation of sunlight by deliberately orienting crop rows could contribute to the resilience of agriculture in the Northeast (and to Northeast SARE’s outcome statement) in multiple ways. First, it could improve the reliability and performance of interseeding—a practice that is rapidly gaining interest as a way for farmers to diversify and improve cover cropping, but which some farmers hesitate to adopt because of inconsistent results. Second, it could buffer against increasingly common moisture-limiting conditions on the more than 80% of annual agricultural acres where cover crops are not used (with the exception of Maryland and Delaware, where adoption is higher). Finally, intentional row orientation shows promise as a non-chemical weed suppressive strategy. All of these benefits come at zero cost.


The evidence behind these assertions is both theoretical and empirical. The theory is simple: in summer, N-S orientation leads to greater sunlight reaching the interrow during the mid-day period while temperatures are highest, while E-W orientation leads to more shading of the interrow area during this period [3, 4]. This suggests that N-S orientation could improve the performance of interseeded cover crops since light is often the most limiting resource as interseeded cover crops get established under a rapidly closing crop canopy. Before his retirement, Penn State scientist Dr. Bill Curran quantified the effect of row orientation on cover crops interseeded into corn at a single site in Pennsylvania and found that a N-S orientation led to 62% higher annual ryegrass biomass in October than E-W (P=0.004; unpublished data); however, additional data are needed to determine the generality of these conclusions across environmental gradients. Conversely, in the absence of interseeded cover crops, N-S orientation allows greater light infiltration, promoting weed growth [5]and increasing evaporation from the soil surface leading to higher moisture stress for crops [6, 7] and . Given the increasing frequency of summer drought in the Northeast [8], this suggests E-W orientation may be optimal in the absence of interseeded cover crops.  


Across the Northeast, there are nearly 13,000 farms growing over a million acres of silage corn. Less than 1% is irrigated, demonstrating that soil moisture-conserving practices are paramount. Silage corn systems have seen a dramatic uptick in cover cropping nationally, from <15% in 2012 to nearly 25% of acreage in 2017. There are over 13,000 farms growing 1.6 million acres of soybeans in the Northeast and 6% is irrigated. Cover crop use in soybeans is less common at 10% [9]. Current row orientation of these acres is unknown, as is the percentage of acres where topography restricts crop orientation. Nonetheless, it is fair to assume that there are tens or hundreds of thousands of acres of corn and soybeans in the Northeast to which intentional row orientation could be immediately and freely implemented.



  1. In the absence of an interseeded cover crop, E-W orientation will lead to higher yields in the majority of sites and years in the Northeast because of increased soil moisture and weed suppression due to shading.
  2. In the presence of an interseeded cover crop, N-S orientation will:
    1. Lead to higher cover crop biomass.
    2. Have limited effect on crop yield because interseeded cover will conserve soil moisture and suppress weeds.
    3. Increase flexibility for timing of interseeding compared to E-W because of greater light availability for before canopy closure.
  3. Cover crop response to row orientation will be species’ specific.
Materials and methods:

To address our research hypotheses, we will conduct three separate, complementary field studies occurring at UNH (main experiment), and two satellite experiments at PSU and UVM. Conducting these experiments at three separate sites, over the first two years of the project will enable us to more effectively evaluate the performance of interseeding cover crops with different row orientations under a range of environmental conditions. In the third year, five on-farm experiments will be conducted by participating farmers with technical assistance from project personnel.  


Treatments: The treatment structure of the main experiment at UNH will be a factorial combination of row orientation (N-S vs. E-W), interseeded cover crop species (no cover crop, annual ryegrass, medium red clover, forage radish, winter rye, and ryegrass-clover and radish-rye mixtures ), and interseeding timing (V4 vs. V6 for corn and R4 vs. R6 for soybeans).  These cover crop treatments have been selected because they are commonly used fall-planted cover crops throughout the Northeast and range in their winter hardiness (because farmers vary in their preference for a winter-killed vs over-wintering cover crops). They also include cover crops that can serve as forages, as livestock farmers are interested in the potential of interseeding to provide an additional source of high-quality forage. Although timing of interseeding has been investigated by other researchers, we feel there is continued need to understand timing because it affects the flexibility farmers have with field operations. Given our hypothesis that N-S orientation may increase flexibility of timing, a timing component of the experiment is a necessity. These choices have arisen from discussions with individual farmers, but we will have additional discussions with the advisory committee prior to commencing research to finalize treatments. Year 1 will be silage corn and year 2 will be soybeans.   

Penn State and UVM will have a subset of treatments (approximately 4-6 treatments) at each of their experiment stations as determined by the advisory committee and collaborators. Each on-farm experiment will be designed by the farmer in collaboration with project personnel.


Methods: Conducting a field experiment with varying row orientation presents multiple challenges when incorporating agronomic realities into the experimental design (e.g. room for tractor to turn around without interfering with neighboring plots). In order to accommodate the physical constraints of row orientation and the necessary field operations, we will use a split-plot design in which row orientation is the main factor, but N-S plots are physically separated from E-W plots. Within each main plot, we will have split-plots consisting of a factorial of interseeded cover crop species and interseeding timing, randomized to experimental units that are each 4 rows (10ft) x 20 ft long. There will be four blocks at each site, which may occur in multiple fields to accommodate the large area required for such an experiment (see supplement).


Cash crops (silage corn and soybean) will be no-till seeded following a burndown application of glyphosate and will be fertilized according to soil test recommendations. Crops will be glyphosate resistant (Roundup Ready, which is the dominant practice throughout our region), and glyphosate will be applied prior to interseeding. To better investigate the effects of row orientation on weeds, no pre-emergent herbicides will be used. This weed management strategy differs from some standard practices, but we feel the increased ability to understand the effects of row orientation on weed populations is worth the tradeoff of deviating from a more typical farmer practice.


We will select short season varieties with upright or semi-upright leaf architecture as has been recommended by previous research from UVM and Penn State. Plant populations will be on the low side of recommendations (e.g., 30,000 plants/acre for silage corn; 130,000 for soybeans) as has also been shown in previous research to increase cover crop performance without a substantial decrease in yield. Cash crop rows will be planted on 30 inch (76.2 cm) spacing, which is standard throughout the Northeast. Cover crops will be interseeded in three rows between crop rows using a Penn State Interseeder or Dawn DuoSeeder (depending on site) following seeding rate recommendations.


Data collection: We will measure soil volumetric moisture content, photosynthetically active radiation (PAR), cash crop yields, cover crop biomass, and weed biomass and species composition.


Soil moisture: Soil volumetric water content will be measured to a depth of 5 cm with a capacitance sensor at a minimum of four timepoints throughout the growing season, timepoints will be targeted to when we expect soil moisture to be at a deficit.


PAR: PAR will be measured using an Accupar LP-80 PAR meter (Meter Group) at hourly intervals throughout the day on two days in the growing season and at mid-day on an additional two days in the growing season.


Cash crop yields: Crop yields will be harvested from a 10ft section of the middle two rows from each plot, weighed fresh, and a subsample will be dried at 65° and then weighed to determine moisture content. 


Cover crop and weed biomass: Cover crop aboveground biomass will be measured in the fall (after cash crop harvest) and the following spring. Weed aboveground biomass will be measured prior to interseeding and at the two cover crop biomass harvests.  Three separate 0.10 m2 quadrats per plot, each covering one of the three interseeded cover crop rows, then separated to species, dried at 65°C, and weighed. 


Measurements of soil moisture, PAR, and cover crop biomass will be spatially explicit to account for distance from crop row. In other words, each response variable will be measured at three points in the interrow space (in a transect 0, 19, and 38 cm from the crop row).  


Data analysis and presentation of results: To evaluate how row orientation, cover crop species, interseeding timing, and the interaction between these treatments affect our response variables (crop yield, cover crop biomass, weed abundance and community, and soil moisture and light parameters) we will use linear mixed effect models using the lmer function in the lme4 package in R. Treatments (row orientation, cover crop species, interseeding timing, and their interactions ) will be included as fixed effects, and treatment nested within block will be included as a random effect to account for the split-plot design. Pair-wise comparisons will be performed using the emmeans package, and a Tukey’s posthoc adjustment will be used to control for multiple comparisons.


Several multivariate analyses will be used to assess treatment effects on weed community composition and abundance and to identify individual species for further analysis with ANOVA. Specifically, we will use non-metric multidimensional scaling and PerMANOVA [13, 14] to detect whole-community differences in community structure and relate these to individual treatments and/or plot-level variation in soil moisture and/or light levels.

Our data will be published in three peer-reviewed papers and presented visually in outreach publications. . We anticipate that the subjects of these papers will be 1.) role of row orientation on crop yields, soil moisture conservation, and weed populations; 2.) role of row orientation on performance of interseeding cover crops; and 3.) a review paper on the role of row orientation as an agroecological climate change adaptation strategy

Research results and discussion:

We conducted a field experiment at three sites (NH, PA, VT) in summer 2023. We are still analyzing results. 

Participation Summary

Education & Outreach Activities and Participation Summary

Educational activities:

3 Consultations
1 Workshop field days

Participation Summary:

100 Farmers participated
15 Number of agricultural educator or service providers reached through education and outreach activities
Outreach description:

Carolyn Lowry shared our experiment station research in Pennsylvania during a Penn State Interseeding workshop with farmers. This event was synergistic with other interseeding outreach. 

Heather Darby shared the experiment station research for this project during the Borderview Farm field day in Vermont. 

UNH Farm Services Manager Peter Davis included an overview of this project in the annual corn and forage meeting for New Hampshire farmers sponsored by UNH Extension. 

Learning Outcomes

Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:

We have not collected any data in this area as we are in the first year of our project. 

Project Outcomes

1 Grant applied for that built upon this project
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.