Long-term cover crop experiment: How much difference do cover crops make?

Principal Investigator: Laura Van Eerd

Research Institution: University of Guelph

Timeline: April 2017 – March 2022

Objectives:

• Quantify the effect of long-term cover crop use on crop productivity and nitrogen (N) dynamics.
• Compare crop yield variability over multiple years with and without cover crops as related to economics and resiliency.
• Quantify total carbon (C) inputs based on planting date over multiple years, to provide Ontario cover crop data for modellers of carbon sequestration.

Impacts:

• Knowing the long-term impact (positive or negative) of cover crops on crop yield and yield stability over the years may assist growers’ management decisions when choosing cover crop practices that maintain crop productivity and competitiveness.
• The generation of carbon inputs and carbon sequestration data based on long-term cover cropping may allow modellers to accurately predict how cover crops may impact carbon and nitrogen cycling under various environmental change scenarios.

Scientific Summary:

While many research questions can be addressed with short term projects, there is a need to evaluate the impact of long-term cover cropping. Cover crops may play an important role in maintaining soil health and influence on carbon and nitrogen stores. But these soil changes can only be detected over the long-term. Ridgetown Campus has two unique state-of-the-art long-term cover crop trials focused on comparing multiple cover crops in Ontario and are among the longest established cover crop trials in Canada and the Midwest USA. Dr. Van Eerd’s long-term cover crop experiment was established in 2007 and repeated in 2008 (Table 1). This was designed to compare four different cover crop treatments (oat, radish, winter cereal rye, mix of rye and radish) and a no cover crop control. The objectives of the trials were to determine the long-term impact of cover cropping on crop yields and resiliency based on known differences in soil health, which were quantified in 2015 and 2016. The main crop plots were evaluated each year for yield, quality, above ground biomass weight, and carbon (C) and nitrogen (N) content. The cover crop plots each year were evaluated for above ground biomass weight and C and N content in the fall and following spring. Finally, soil mineral N was quantified by taking soil samples at main crop planting, harvest and in late fall (November). The project deliverables were to develop cover crop-specific best management practices (BMPs) that identify cover crop species and mixtures that increase crop yield and resiliency.

Outcomes

Recommend cover crops for crop yield and N dynamics: By accounting for N in cover crop residues and mineral N in surface soil (90 cm depth), compared to the no cover crop control, cover crops reduced potential N losses over the non-growing season by 1.9% to 14%. In 2020 to 2021, instead of the tested non-legume cover crops immobilizing N, we observed corn growth and yield was enhanced by long-term cover cropping (grown 10 times in 13 years). By the end of June onward, corn was taller and greener (i.e., lacked nitrogen deficiency symptoms) with some cover crop treatments compared to the no cover crop control. Corn grown in the no cover crop control plots had nitrogen deficiency symptoms (less green, shorter, bottom leaves firing). These visual observations were confirmed by optical sensor data (SPAD meter) where corn leaves had higher readings (i.e., deeper green) in long-term cover crop plots than in the no cover crop controls. Back of envelope calculations using corn grain yield increases suggest that with long-term cover cropping the grain corn crop had up to 90 to 140 Ib N/ac more nitrogen than in the no cover crop control plots. This was estimated assuming 1.2% N concentration in grain and a harvest index of 0.5 (plant weight is half grain and half stover) and based on yield increases of up to 38 and 59 bu/ac. The long-term cover crop treatments used in this experiment were oat, winter cereal rye, radish, and a mix of radish and rye. Due to differences between years, it was not possible to identify the ‘best’ cover crop, thus farmers should select the cover crop that fits their goals.

The mechanism of corn yield increases from long-term cover cropping in this trial is not known. It is worth noting that rainfall in 2020 was considerably lower than normal rainfall until mid-July. For instance, it is not possible to separate the nitrogen effect from drought tolerance. Nor do we know if observed yield increases with long-term cover cropping was due to differences in corn N uptake or soil N availability or both. Further, soil organic matter in the surface 6 inches correlated to grain yield, which supports the notion that healthier soil has a greater nitrogen availability and/or water holding capacity and thus resiliency to moisture stress. Additionally, changes in corn root density and architecture would contribute to nitrogen and water stress. A new project (C2022AG07) has been initiated in 2022 to compare first-time and long-term cover cropping to better understand nitrogen availability to corn.

Deliver cover crop best management practices that increase crop resiliency: Resiliency (ability to yield during stress conditions) was assessed in the dry growing seasons of 2016 + 2020. Cover crops increased soil health and organic matter after growing cover 6 times in 8 years (2016). Tomato yield was positively correlated to soil organic matter/carbon in 2016. In 2020, grain yield positively correlated to soil organic matter (measured in 2019). Thus, improvements in soil health increased yield resiliency in dry years in this experiment. Cover crops were managed in a tillage system.

Deliver best management practices for carbon inputs and sequestration based on long-term cover cropping with data available to modellers: When averaged over the 8 years, this amounted to a carbon storage rate of 1.1 Mg C/ha/yr (corrected for C in the no cover crop control).

Soil heath: Cover crops had soil organic matter (OM) that ranged from 3.7% to 3.9% compared to 3.4% OM in no cover crop control as measured by the Soil Health Institute in 2019. This result was consistent with earlier research in 2015 with medium-term cover cropping. Significantly greater soil health among cover crop treatments compared to the no cover crop control were observed in the medium term (planting covers 6 times over 8 years).

Crop yields: Since 2007, across 32 site-years, we have planted 173 cover crops treatments (i.e., site x year x treatment). 171 times main crop yield was as good as or better with a cover crop than without. In 2020 and 2021, corn grain yields were up to 38 and 59 bu/ac greater with long-term cover crops (grown 10 times in 13 years).

External Funding Partners:

Ontario Processing Vegetable Growers (OPVG)

This project was funded in part through the Canadian Agricultural Partnership (the Partnership), a five-year federal-provincial-territorial initiative.

Additional funding was provided by the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), through the Ontario Agri-Food Innovation Alliance.

The Ontario Crops Research Centre – Ridgetown is owned by the Government of Ontario through its agency, the Agricultural Research Institute of Ontario, and managed by the University of Guelph through the Ontario Agri-Food Innovation Alliance.

Project Related Publications:

Bagnell, D., Morgan, C.L.S., Cope, M., Bean, G.M., Cappellazzi, S.B., et al. 2022. Selecting soil hydraulic properties as indicators of soil health: Measurement response to management and site characteristics. Soil Science Society of America Journal. 86 (5), 1206-1226.  https://doi.org/10.1002/saj2.20428.

Bagnall, D.K., Morgan, C.L.S., Cope, M., Bean, G.M., Cappellazzi, S., Greub, K., Liptzin, D., Norris, C.L., Rieke, E., Tracy, P., Aberle, E., Ashworth, A., Bañuelos Tavarez, O., Bary, A., Baumhardt, R.L., Borbón Gracia, A., Brainard, D., Brennan, J., Briones Reyes, D., Honeycutt, C.W. 2022. Carbon-Sensitive Pedotransfer Functions for Plant Available Water. Soil Science Society of America: Journal 86:612-629.

Chahal, I. 2022. The cover crop difference. Ontario Grain Farmer. February 2022.

Chahal, I. and Van Eerd, L.L. 2021. Cover crops increase tomato productivity and reduce nitrogen losses in a temperate humid climate. Nutr Cycl Agroecosyst: 119:195-11.

Chahal, I. and Van Eerd, L.L. 2020. Temporal dynamics of soil health indicators using a medium-term cover crop experiment in a temperate, humid climate. PLOSone: 15(7): e0235665.

Chahal I. and L. L. Van Eerd. 2019. Quantifying soil quality in a horticultural-cover cropping system. Geoderma: 352, 38-48.

Chahal, I. and Van Eerd, L.L. 2018. Evaluation of commercial soil health tests using a medium-term cover crop experiment in a temperate climate. Plant and Soil: 427:351–367.

Chahal, I., Vyn, R.J., Mayers, D. and Van Eerd, L.L. 2020. Cumulative impact of cover crops on soil carbon sequestration and profitability in a temperate humid climate. Nature Scientific Reports: 10:13381.

Collingwood, A. 2020. The impact of cover crops in processing vegetable-grain cropping system in Ontario, Canada. Field Crop News: March 18, 2021.

Dietz, J. 2017. Cover your ground – and a lot more – between crops. Top Crop Manager: September 26, 2017.

Hannam, R. 2021. Long-term cover crop research: new yield findings. Ontario Grain Farmer: April 2021.

McIntosh, M. 2020. The economics of cover crops: Ridgetown research highlights profitability gains and losses in grain and vegetable systems. Farmtario: October 7, 2020.

McNaughton, K.E., and Van Eerd, L.L. 2018. Cover crop best practices: what to plant and how to get rid of it. Top Crop Manager: November 8, 2018.

Rieke, E.L., Cappellazzi, S.B., Cope, M., Liptzin, D., Bean, G.M., Greub, K.L.H., Norris, C.E., Tracy, P.W., et. al. 2022. Linking soil microbial community structure to potential carbon mineralization: a continental scale assessment of reduced tillage. Soil Biology and Biochemistry: 168:108618.

Tobin, B. 2020. Putting a value on cover crops and soil health. RealAgriculture: December 22, 2020.

Tosi, M., Drummelsmith, J., Obregón, D., Chahal, I., Van Eerd, L.L. and Dunfield K.E. 2022. Cover crop-driven shifts in soil microbial communities could modulate tomato early crop growth via plant-soil feedbacks. Scientific Reports: 12 (1) :1-13

Trueman, C.L., J.C. Awrey, A. Delaporte, J. Kerr, A. Weersink, L. L. Van Eerd. 2023. Long-term cover cropping suppresses foliar and fruit disease in processing tomatoes. Plant Disease -In Press. Manuscript ID PDIS-09-22-2095-RE

Table 1. The crop rotation and effects studied at the long-term cover crop experiment at Ridgetown, ON.

Year		Main crop	Post-harvest management1	Split plot effect2	Split-split plot effect2	Reference
Site A	Site B
2007	2008	fresh pea	cover crops
2008	2009	sweet corn	cover crops	fertilizer (0 /140)	weed control (+/-)	O’Reilly et al. 2011, 2012
2009	2010	spring wheat	cover crops
2010	2011	tomato	cover crops	fertilizer (0 / 140)	tomato cultivar	Belfry et al. 2017
2011	2012	grain corn	remove/retain stover
2012	2013	acorn squash	cover crops	residue mgmt (+/-)		Ouellette et al. 2016
2013	2014	soybean	winter wheat
2014	2015	winter wheat	remove/retain straw + cover crops
2015	2016	tomato	cover crops	residue mgmt (+/-)		Chahal and Van Eerd 2018, 2019, 2021; Chahal et al. 2020; Tosi et al. 2022
2016	2017	fresh pea	cover crops
2017	2018	sweet corn	winter wheat
2018	2019	winter wheat	remove/retain straw + cover crops
2019	2020	tomato	cover crops	residue mgmt (+/-)	fertilizer (0 / 140)	Trueman et al. 2023
2020	2021	grain corn

¹Cover crop treatment was the main effect, which consisted of a control (no cover crop) and four summer/fall-planted treatments: winter cereal rye, radish, oat and a mixture of oilseed radish and winter cereal rye.

²Split plot and split-split plot effects were studied in the main crop.