Study of ramial chip mulch and organic fertilizers on wild blueberries

Study of ramial chip mulch and organic fertilizers on wild blueberries

Summary

There are very few options for organic wild blueberry growers when it comes to fertility management.  Organic fields tend to have high populations of weeds (like grasses, broadleaf perennials, wildflowers, woody and herbaceous plants, and tree saplings) which become established in and amongst the low-bush blueberry plants, and readily outcompete the blueberries for nutrients.  When an organice grower seeks to promote nutrient uptake and yield for the blueberries with applications of approved fertilizer, it is the weeds who receive the boost, not the blueberries.
   Our project is studying the effect of one type of mulch material (ramial chips) in tandem with a selected fertilizer package (fishmeal and aragonite), and following three separate applications rates (plus a control) through two harvest cycles.  It is a four year study, which began this year and will be complete in 2017 (as the production cycle of the wild blueberry is a two-year cycle).  We will be ultimately looking at nutrient levels and yields over the sixteen plots (four replications of four treatments), and comparing that data to costs per treatment by way of enterprise budgets.  We are looking for an effective way to simultaneously control weeds and fertilize the wild blueberry plants, using the combination of mulch and fertilizers to tip the competition for fetililty in a diverse plant ecosystem in favor of the wild blueberry.
   In the spring of 2014, we laid out and established the research plots, and performed all the various treatments for each.  Our technical advisor, Marianne Sarrantonio of the Univ. of ME, has not yet participated in the project, as we have not yet begun to record or analyze data.  That work will begin in 2015, with the first of our two harvests for the study.

Objectives/Performance Targets

In late April of 2014, I began setting up and laying out our sixteen test plots.  Each one is 12’x50′, and I left a 4′ alley between each plot to minimize spillover or “drift” of mulch or fertilizer from plot to plot.  The treatment plots were laid out at random, so neighboring plots vary from each other across the entire study area, which totals about 1/2 acre.  I originally used small plastic flags on fiberglass posts to mark the boundary corner of each plot.
   Prior to laying out and establishing the plots, most of the study area had been mowed (a standard pruning technique), while the rest of the five acre field was burned (the alternative pruning technique).  Our study originally proposed having the test plots all in the similarly managed area of the field, to reduce the number of variables that could affect our results.  Unfortunately, the 16 test plots could not readily fit within the mowed area of the field, so I have established four of the plots in an area that was burned (one replication of each treatment).  The different pruning techniques may or may not alter the plant growth and yield –but either way, I have clearly noted on the test map of the plots which ones had been mowed and which ones had been burned.
   Over a four week period in May, I cut saplings (predominantly gray birch) on our farm from areas where they’d become densely established over the past 20 years, thereby opening up former field space.  Most of the saplings were smaller than 3″ in diameter, not yet leafed-out, and everything up through the tiniest of branches was chipped, resulting in what is known as “ramial chips.”
   The ramial chips were then spread to a depth of 2″ to 4″ on twelve of the 16 test plots (our control treatment in the study, replicated across four plots, has no mulch or fertilizer applied).  In low spots and hummocky areas, I often allowed the mulch to accumulate to depths up to 8″, thereby helping to level out the surface of the field, a condition which helps make future harvesting and pruning work more efficient.
   Just prior to spreading the mulch on eight of the plots (the ones where I had planned the replications of two different treatments of fertilizer applications), I spread the appropriate amounts of fishmeal and aragonite.  One treatment over four plots had a rate of 12 lbs./plot (or the equivalent of 70 lbs./acre of N) of the fishmeal and 2 lbs./plot (or 150 lbs./acre of Ca) of the aragonite.  The second treatment over four plots had half those rates (6 lbs./plot of fishmeal and 1 lb./plot of aragonite).  The fertilizer was weighed in a hanging scale, and spread evenly over the plots by hand.  Then, the ramial chips were immediately spread over the top of the fertilizer.
   I found the work of producing and spreading the ramial chip mulch to be accomplished in less time than I had estimated.  Although it is time-consuming and difficult work, I am happy in light of developing enterprise budgets for this study that the labor costs could be lower than originally thought.
   By the time I was chipping and spreading the ramial chip mulch on the last few test plots, the gray birch saplings had begun to leaf-out, which could alter, among other things, the C:N ratio of the ramial chips, and therefore change their chemical, biological and/or physical attributes in the study.  This may or may not have an affect on the results of our project, but either way, I have noted these plots on the test map of our field.
   Our original proposal included gathering baseline data during the first summer of the study (2014), including soil test analyses, foliar nutrient analyses, and Brix readings of foliage from each plot.  Due to illness and an extremely busy farm season (it was a banner year for the wild blueberry harvest), I was unable to perform these tests.  This is unfortunate, as I will not be able to compare the results of later tests with the starting data.  However, I do have some data (soil and foliar analysis) from this field from 2010, which I will be able to use, as well as the harvest data from the field going back to 1998.  Our final analyses and outcome for the project is primarily comparative, treatment to treatment, so the baseline data, though important and interesting, is not imperative; all of the plots are in the same limited area within a field that has been managed in the same manner for almost 20 years.  I do plan on performing all of the tests on all of the plots from now on, as originally proposed.
   Finally, for 2014, I realized by late summer that the marking flags I had chosen were not going to be sufficient for a four year study.  Some of the flags had already torn, and most had faded dramatically in the sun; there were also several that had blown over or been lifted out.  So, I purchased some iron rod rebar, cut it to 2′ lengths, spray painted these new stakes in four different colors (to mark and correspond with the four different treatments), and installed them in replacement of the original corner boundary markers.  These stakes are more permanent for our study, and give instant identification as to which treatment one is looking at for each plot (as they are now noted on the test map).

• April 2014: established test plots
• making ramial chips
• preparing to spread fertilizer
• 12’x50′ test plot
• close-up of spread ramial chips

Accomplishments/Milestones

As noted above in “Objectives/Performance Targets,” a few variables were inadvertently added in to the study: viz., different pruning techniques (mowing vs. burning) were performed on different plots prior to the study, and the composition of the ramial chips changed over the course of making and establishing all of the test plots as spring inevitably unfolded and the hardwood trees began to leaf-out.  No obvious, observable differences can be seen at the end of 2014.  How these conditions may affect the results of our study has yet to be observed or measured; at any rate, the variables are noted on our map of the test plots, and can readily be identified and tracked in the future.
   By late fall, one could observe that the ramial chip mulch has certainly influenced the weed population in the plots.  Across all of the plots, the mulch can be seen to have smothered short grasses and wildflowers quite effectively.  The blueberry plants have successfully grown through the mulch, with little observable difference in growth between the different treatments.  Some weeds, such as huckleberry, aronia, bunchberry, bay, and tree saplings, have been able to grow through the mulch.  Overall, I was pleased but not surprised to see the mulch did not inhibit the blueberries while it did inhibit some weed growth in this first season.

Impacts and Contributions/Outcomes

I have shared my SARE Grant project’s purpose, goals and objectives at several meetings and opportunities over this past year, including several MOFGA meetings and events, at the annual organic wild blueberry growers’ gathering hosted by the Univ. of ME Extension in July, and in personal conversation with other growers, friends and blueberry customers.  Across the board, there is great interest in the study, and desire to know and share the outcome.

Collaborators: