Biodegradable Mulch: Does it Make the Grade?

Monday, November 30, 2020

 Biodegradable mulch and bioplastics are buzz words heard fairly often in today’s social climate of reducing waste and replacing some of our traditional materials with more eco-friendly options. There are many products out there claiming to be compostable or biodegradable, but what does that actually mean?

One of the biggest concerns with some of the plastic products claiming to break down in the environment is that they never fully break down and instead result in microplastics, which can cause even more problems down the line. So, what is a biodegradable mulch?

The major indicator of what constitutes a biodegradable mulch is the degradation process and the resulting products. Degradation is the measurable conversion of mineralized carbon to CO2, resulting in a change in the chemical structure, physical properties, or appearance of the material. This is a very important point since the degradation of biodegradable mulch results in the complete breakdown of the material into biomass and CO2 rather than microplastics. It’s important to note that biodegradable is not the same thing as photodegradable (breaks down with light) or oxodegradable (breaks down by oxidation) plastics, both of which are made up of conventional plastics.

Photo: Dubois Agrinovation

Biodegradable mulch is designed to be tilled into the field after use and relies on certain material properties and environmental conditions to facilitate degradation such as temperature and presence of microorganisms.

A study conducted through Washington State University Extension looked at the impact of soil-biodegradable plastic mulch on soil health and quality. The soil health assessment was based on indicators relating to structure, hydrology, biology, chemistry, fertility and salinity/sodicity. Field plot treatments were four different biodegradable plastic mulches, a biodegradable paper mulch, a conventional polyethylene mulch and bare ground. The biodegradable mulches were applied annually in the spring and tilled into the soil in the fall for 2-4 years. The overall findings indicated that the various biodegradable mulch products did not negatively impact overall soil health. However, it should be noted that long-term evaluations are required to form more solid conclusions.

A separate study looked at the presence of visible mulch fragments after four years of mulch applications and one year of rest as a measure of initial mulch degradation. As little as 20% of the original volume of mulch remained in the soil in a recoverable form (fragments large enough to be separated from the soil with a 2mm sieve), proving that degradation is taking place. Although this measurement wouldn’t indicate the rate or extent of degradation, the materials that make up the mulch will eventually degrade into CO2 and biomass, so would not be at risk for contributing microplastics to the soil environment.

There are some important things to consider when thinking about switching to biodegradable mulch from traditional plastics. Biodegradable mulch typically has less elasticity and strength than polyethylene mulch, so field conditions need to be appropriate so there isn’t extra strain being placed on the mulch, which could cause it to tear. Appropriate field conditions would include a smooth seedbed that isn’t saturated with water to form clods, and no big rocks. The mulch should be laid looser than you would a plastic mulch as it will tighten up a little under field conditions. Trials in Washington State showed that vegetable yields under biodegradable mulch were equal to those under plastic mulch and generally better than on bare ground. Weed suppression with the biodegradable mulch did not always measure up, however. Since the mulch should be fairly brittle by the end of the season, it should easily break into pieces during rototilling and not clog up the equipment.

For more information about biodegradable mulch or for more detail on the studies mentioned in this post, visit Washinton State’s Small Fruit Horticulture Research and Extension Program and University of Tennessee Institute of Agriculture’s Biodegradable Mulch page.

Nitrogen Savings in Winter Spinach Production

Tuesday, September 29, 2020

 By: Talia Plaskett, Protected Crop Specialist 

As summer production of tunnel vegetables slows down, it is time for winter greens to move on into the greenhouse! Spinach, along with a variety of other cool season greens, can be grown in high tunnels throughout the offseason. This allows you to maximize your use of the otherwise empty greenhouse space without cutting into the production of your summer crops.  A recent study done by the Northern New York Agriculture Development Program (NNYADP) examined the effect of nitrogen(N) fertilizer rates on winter-grown, high tunnel spinach production.


A study out of New York examined the effect of nitrogen rates on winter-spinach - photo credit Johnny's Seeds


 
In the winter of 2018-2019, they examined the effect of different pre-planting N applications on overall spinach yields. The same N source was used across the four treatments, allowing them to make direct comparisons to yield based on input.  Rates of 0 lbs/ac, 65 lbs/ac, 130 lbs/ac or 200 lbs/ac were applied to their treatment plots about 1 week prior to transplanting the spinach. Plants were seeded in two batches, one on August 27 (early planting) and one September 10 (late planting). These were transplanted into the tunnel on September 21 and October 9, respectively. Yield measurements were based on harvesting the plants at the baby-medium leaf stage at 4 dates.  


When looking at the total yield for each treatment, there was no significant difference between those plots that received 0 lbs/ac and those treated with 200 lbs/ac. Planting date did make a difference to the spinach harvested in the fall and in the winter, where the early planting produced more compared to that of the later planting. Over the course of the season, however, the later planting caught up to the earlier one, to produce similar yields by the April harvest date. The importance of the planting date may depend on when your summer crop is pulled in the fall, and when the subsequent summer crops are started in the spring. If you plan to have your summer transplants started by late winter (February/March), a later planting of winter greens may not have the time to catch up to the production of the earlier planting.  


For more information on the study, check out “Nitrogen Uptake in Winter Spinach”, part of the Northern New York Agricultural Development Program 2019 Project Report". 


If you are interested in winter greens production, check out the Into the Weeds, Winter Greens Production’ session posted on Perennia’s YouTube channel or reach out to a specialist!  

Brushing Up On Storm Prep

Friday, September 18, 2020

 Many of us have unpleasant memories of last year’s Hurricane Dorian and its effects on the many crops that were still waiting to be harvested when it hit Nova Scotia on September 7th, 2019. As we stare down the barrel of Teddy, which is currently predicted to make landfall in Nova Scotia as a post-tropical storm on Tuesday, September 22nd, those unpleasant memories may come rushing back. Thinking about another approaching system might bring up some anxiety, but there was also a lot to be learned from last year’s hurricane.

Environment Canada hurricane track map issued 12:00pm September 18th, 2020.

Get Your Storm Chips (and Produce)

It isn’t practical to think that everything can or should be harvested prior to a storm system, however, crops that are most vulnerable to weather extremes can be prioritized in order to save as much of the crop as possible. Things like cucurbits and field tomatoes are prone to splitting after heavy rain, so would fall high on the list of things to harvest first. Consider postponing seeding new plantings or cover crops in the days leading up to a significant storm. Wind and pounding rain can cause erosion and flooding, which could easily dislodge tender seedlings or wash away the seed altogether.

Batten Down the Hatches

Greenhouse or high tunnel structures can be dealt with in a couple of different ways in the face of an impending storm, both with their advantages and disadvantages. If there is an option to remove the plastic from a structure, the chance of being caught by the wind and potentially ripping or acting as a sail and damaging the frame of the structure can be significantly reduced. The downside to this option is that the crops beneath are exposed to the elements which may result in crop damage and loss.

If removing the plastic isn’t an option, make sure everything is sealed up as much as possible to prevent the wind from tearing things loose and wreaking havoc. Latch and brace doors and tie the sides of tunnels down tight. Most structures will have a rating for maximum wind speeds they can withstand. Take into consideration any shelter/exposure provided by the topography of your farm as well as the up to date weather forecast to help make an informed decision.

If you have a generator, make sure you have plenty of fuel and that it’s in an accessible place. If you don’t have a generator and require power for your watering system, make sure you have some water set aside in barrels in case of emergency.

The Aftermath

Besides damage by wind and heavy rains, disease issues can be a big consideration after a storm event. Heavy rain can splash fungal spore or bacteria-containing soils around, facilitating the spread of infection. Crop protectant products may be washed away, leaving the plants vulnerable until they can be sprayed again, if at all. Wind and rain may cause physical damage to the plants themselves, causing them stress and areas of damage where infection can move in. High winds sweeping up the coast may even carry insects from elsewhere, resulting in a flush of insect pressure that would otherwise be unexpected. It is important to scout your remaining crops as soon as possible after a storm has passed so that there is opportunity to mitigate any pest pressure brought on by or worsened by the weather.

I hope that this post will be like remembering your umbrella when it’s forecast to rain: you won’t end up needing it. In the meantime, keep track of the forecast and plan ahead as much as possible while we wait to see what else 2020 might have up its sleeve.

Soil Salinity in High Tunnels

Thursday, September 10, 2020

drought stress on tomatoes
Drought stress on tomato leaves. Soil salinity can cause
increased susceptibility to drought stress in plants. 
Photo: Long Island Horticultural Research & Extension Center
Soil salinity can occur in high tunnel production due to some of the characteristics unique to this type of growing system. High tunnels are often used as a season extension tool, meaning that they are in production for a longer period of time and managed more intensively than a typical field. This management can include fertilizer applications, irrigation, and heavy traffic leading to compaction and poor drainage, all of which contribute to salt buildup in the soil.

The other major difference between tunnel and field production with an impact on soil salinity is that the ground under tunnels is protected from the elements, most notably precipitation. In a field situation salts would have more opportunity to be flushed through the system by rainfall, while tunnels aren’t able to take advantage of this type of natural cleansing. 

Soil salinity is a concern for a number of reasons including that plants in saline soils are more susceptible to water stress, which is particularly prevalent in a year with so little excess water around anyway. Saline soils can also lead to salt injury in plants and adverse affects on soil structure. It is important to monitor the salt levels of your soil and take preventative measures to avoid excess buildup. Some strategies for preventing or managing saline soils include utilizing mulch to reduce evaporation from the soil, deep tillage, and exposing the soil to rain by removing the plastic from the tunnel. As you start to think about coming to the end of the production cycle, it might be a good time to employ some of these strategies or plan preventative measures for next season.

For more information, check out Perennia’s factsheet: Soil Salinity in Nova Scotia High Tunnels.

Late Summer Scouting and Beneficial Insect Release

Thursday, September 3, 2020

 As the air starts to move away from the heat of the summer and into cooler fall temperatures, it’s important to continue scouting your high tunnels and greenhouses for insect pests. Although the days for your crop may be numbered, many insect pests overwinter in the ground or in the debris in and around the growing space as a part of their life cycle. The more insects that overwinter successfully, the higher your pest pressure will be on next year's crop. Once pests start slowing down and hiding away for the colder months, the window of opportunity for controlling these pests closes. Beneficial insects typically do not survive the winter months, so planning to release them late summer can help to reduce pest populations while they are still active and reduce their population sizes for the following spring. For those pests that do remain active in the colder weather, it is important to keep those numbers low in the fall to limit pest pressures throughout the colder months. 

During the harvest season, it can be difficult to maintain a scouting program due to the sheer volume of work to be done on any given day. However, it is important to remember that the early days of new crop are critical, and ensuring your plants have every advantage they can get is crucial to a successful and high yielding season. Taking that extra time to scout and release beneficials will pay off in the long run and mean less headache in the coming year.  

Cornell University Extension in New York conducted on-farm applied research on Aphid Management in Winter Tunnel Greens which offers some practical insights into late season integrated pest management.