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 organic 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 in 2014 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 fertility in a diverse plant ecosystem in favor of the wild blueberry.

2015 saw the first harvest year in our study allowing us to begin the gathering and analyzing of data.  Our technical advisor, Marianne Sarrantonio of the Univ. of ME, has not yet participated in the project; we will likely ask her to make a field visit during the second prune cycle next year.  Our goals and objectives and outreach plan for this project remain relatively unchanged up to this point.

Objectives/Performance Targets

We successfully gathered useful data from the first of the two harvest cycles that this study encompasses (the second harvest cycle will be in 2017).  The data includes harvest yields from each test plot, which have then been analyzed, as well as Brix readings from the ripe fruit taken from each plot.

In mid-May, we set four hives of honey bees on the field for a period of several weeks while the blueberry plants were in bloom, and had good weather plus notable healthy numbers of native/wild pollinators to ensure good pollination for the year.  Just prior to harvesting, in late July, we strung the boundaries of each of the sixteen plots (with white string) to clearly mark the edges of each.  On August 3rd, we harvested the blueberries from all of the alleys between and surrounding the plots; then on August 4th and 5th, we harvested the plots.  The berries from each plot were harvested into clearly marked field totes, which were then gathered together and brought to our winnower shed.  The field totes from each individual plot were then processed through our fresh-pack line (i.e., winnower), and the total weight of processed berries from each plot then measured and recorded.  At this time, a small sample was taken from each plots’ winnowed berries, which were then placed in labeled zip-lock bags in our cooler; several days later, we used our refractometer to measure and record the Brix level of each sample.  All of these numbers have been gathered and analyzed in several matrixes, and now serve as the foundation set of data which will be compared and contrasted to our pre-test baseline data and the second set of test data yet to be collected.

Due primarily to continued illness (Lyme disease), we were not able to perform all of the data gathering from our original proposal this year.  Namely, we did not collect weekly Brix readings of the fruit for up to five weeks (from early ripening through harvest), but rather only collected the one Brix reading at harvest.  Also, we were not able to collect Brix readings from the plant tissue from each plot.  Our intention is still to collect this data, as well as the proposed soil and foliar analyses tests, during the second prune and harvest cycles in 2016 and 2017 respectively.

Accomplishments/Milestones

The collected data from this first harvest year, though interesting and compelling, has not given us the ability to draw any strong conclusions, which does not surprise us and underscores the value of having secured research funding through two harvest cycles.  What we have found in this first year’s work is that the efficacy and impact of our treatments will take some time to express themselves clearly, and that although there are some clear differences in comparing different treatment plots’ data, there is no clear relationship between any given treatment and any given result. 

In general, there are still many naturally occurring factors which could reduce or make any statistical significance between the harvest data or the Brix readings from the various plots very slight.  These factors include the genetic traits of the blueberry clones themselves in any given plot or area of the field, plus the underlying soil type, and naturally occurring weeds present, etc.  All of these factors were expected to influence yield and nutrient data, and we randomized our plots to allow for such natural variation.  Nonetheless, we have observed such things as an area of our field where five adjoining plots have the highest yield data, and another area of our field where five adjoining plots have the lowest yield data.  What’s more, the ramial chip mulch is still very present (not decomposed or otherwise broken down) and is therefore negatively impacting the ease and ability to cleanly harvest the ripe berries, and is likely tying up nutrients in the soil as it continues to decompose.  We hope and expect these conditions to change, and the data resulting from the harvest in 2017 to reveal more telling relationships to our treatments.

Here are some of the more interesting analyses from this year’s data:

1. The control plots (no treatments) had the highest yield overall (total of all four plots), with 149.93 lbs. total, and average of 2,717.48 lbs./acre equivalent.  That compares to the mulch only plots with 135.76 lbs. total and 2,460.65 lbs./acre, the mulch and half-rate fertilizer plots with 130.30 lbs. total and 2,361.69 lbs./acre, and the mulch and full-rate fertilizer plots with 127.56 lbs. total and 2,312.03 lbs./acre.  Again, we believe the mulch may still be negatively effecting the yield and will wait to see what the second harvest year’s data reveals.
2. There was very little difference between plots that had been burned (as a pruning technique) and those that had been mowed.  The burned plots averaged 33.75 lbs. total each and 2,449.89 lbs./acre, while the mowed plots averaged 34.05 lbs. total each and 2,471.85 lbs./acre.
3. There was a slight difference between plots that had been mulched with proper ramial chips (made with dormant, non-leafing hardwood) early in May of 2014 and plots that had been mulched with hardwood that had already leafed out later in May 2014 (a condition which we believe effects the C:N ratio of the chipped wood, and therefore the chemical, biological and physical properties and effects).  The non-leafed out ramial chip mulched plots averaged 37.10 lbs. total each and 2,693.10 lbs./acre, while the leafed-out ramial chip mulched plots averaged 28.51 lbs. total each and 2,069.71 lbs./acre.  The proper ramial chips appear to have better effect.
4. The Brix readings of the ripe fruit from the mulch only plots averaged the highest, with an average of 11.3.  The mulch and full-rate fertilizer plots had a 11.1 Brix average, the mulch and half-rate fertilizer plots had a 10.6 Brix average, while the control plots had the lowest Brix average of 10.2.  These are all lower than baseline data we have from previous years’ ripe fruit which is typically between 12 and 14 Brix.
5. The highest yielding plot was a control plot with 55.44 lbs. total (4,024.94 lbs./acre equivalent).  The lowest yielding plot was a mulch and full-rate fertilizer plot with only 23.57 lbs. total (1,711.18 lbs./acre).  The highest Brix reading came from a mulch only plot with 12.2.  The lowest Brix reading came from a control plot with only 9.8.

• test plot with ramial chip mulch

Impacts and Contributions/Outcomes

Nothing new to report.  As with last year, we have continued to engage in conversation about this project with other wild blueberry growers, extension agents, and other intersted parties, at farm meetings, MOFGA meetings and events, etc.  Our outreach plan remains as first proposed.

• harvesting the research plots

Collaborators: