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OMAFRA: Are there risks to planting corn after cereal rye?

There has been interest in rye as a cover crop or to maximize yields in silage systems where rye can be harvested for silage by mid- to late May, which still allows time to plant a corn silage crop. Benefits of rye include good winter hardiness, early maturity and high yield relative to other winter cereal forages. Benefits of this system include potentially higher yields than a single corn silage crop and ground cover nearly all year long. Rye gets a bad rap when followed by corn, however – how true is this, and what options reduce risks?

What does the yield data say?

Yield responses are variable, and likely dependent on environmental and management practices. Some work in the Great Lakes and northern corn belt regions has shown yield loss when planting corn after rye, averaging 11-17 per cent in past Ontario research, while research shows minimal loss. In a silage system, the question becomes whether the yield loss due to planting corn later can be offset by the yield of the rye forage crop. Some research – but not all – suggests this is possible.

What causes yield loss?

The mechanisms of yield loss, when it does occur, are not well understood. A few things that receive attention as possible causes for corn yield loss following rye include:

• Allelopathy or toxicity from decaying rye from compounds released or formed following decomposition. The impact of allelopathy is suggested to be highly variable depending on amount of rye residue, soil type, temperatures and moisture at termination. Some suggest that while rye can produce allelopathic compounds, impacts on corn growth may be over-emphasized; due to corn’s large seed size and relatively deep planting depth away from the soil surface, allelopathic impacts may be minimal.
• Plant root diseases bridging from decaying rye roots to developing corn seedlings, particularly if conditions are favourable for pathogen development (cold, wet) and populations or inoculum are already high. Authors have shown that root diseases that proliferate on decaying rye roots can also infect corn, and that corn root diseases, growth and plant stand issues can be more pronounced with rye cover crops terminated shortly before corn planting, compared to a couple weeks prior.
• Seedbed environment. Early in the season, rye biomass may limit soil warming and drying, creating challenges for planting and seedlings – particularly in cooler and wetter springs. In silage scenarios, dry weather during rye’s later vegetative growth stages, when evapotranspiration is high, may result in significant soil moisture loss, creating planting, germination and crop uniformity challenges. Under no-till, dry conditions and rye root structure may cause opener, seed depth and slot closure issues, exacerbating seedbed dryness and introducing other challenges for developing seedlings (lack of moisture, temperature variability/extremes, desiccation, root establishment).
• Nitrogen supply, given significant nitrogen uptake and immobilization as rye biomass decomposes. Nitrogen responses have been variable. Some research has found rye to tie up nitrogen and for corn following rye to require more nitrogen, while other research has not. Past Ontario research has shown increasing nitrogen rates could sometimes yield more corn, but could not close the yield gap for planting corn after rye.

How do you limit risks?

Clearly there is no single silver bullet solution for removing the risks of planting corn after rye, but some suggestions from past research include:

• Avoid planting rye in close vicinity to next year’s corn rows (e.g. “bio-stripping”) to reduce allelopathy and disease risks, though this may fit better in cover crop scenarios where rye yield is less important.
• Terminate/harvest rye early or leave time (i.e. one to two weeks) between termination and corn-planting, as this improves corn performance relative to planting corn immediately after rye termination/harvest. Advantages of this could be greater probability of planting under better conditions, time for allelopathic compounds to dissipate, or soil moisture conservation with earlier rye termination/harvest. This approach may not always be feasible, particularly in silage scenarios where yield potential of both rye and corn are of concern.
• Earlier rye harvest (before boot stage) during springs with low rainfall is cited as one method of limiting seedbed moisture losses and improving corn establishment, though at the expense of rye yields. Quality of ryelage will be higher if harvested early.
• Past research in Ontario has not shown rye residue removal (silage harvest versus clipping top growth on surface) to have a strong impact on reducing yield loss when corn follows rye, but markedly improved corn performance has been observed when rye residue and first centimetre of soil are removed with planter-mounted disc furrowers.
• Ontario research demonstrated a strong yield response for tillage compared to no-tilling corn directly into silage-harvested or clipped rye, and the yield advantage of including rye in a corn silage system hinged on this tillage yield. If reduced tillage is preferred, a delay between rye termination/harvest is more important, and a planter capable of handling seedbed conditions is critical – sufficient down pressure, opening and depth control, and being able to properly close the trench.
• Nitrogen management was never a panacea, but it’s important to have a program that will reduce risks under high-residue conditions. This likely includes starter nitrogen, a reasonable amount of nitrogen at planting or ensuring any delayed applications are made on a timely basis, and avoiding surface broadcasting nitrogen on high-residue ground.