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.

2016 saw the second prune cycle year in our study.  We burned all of the plots in our field in April, allowing new vegetative growth to come up, eventually producing the buds for next year’s harvest in the fall.  Data was collected in mid-summer with foliar samples being harvested and sent to UMaine for nutrient analysis, followed by soil samples being taken in early fall and sent to both UMaine and an out-of-state lab for analysis.   Our technical advisor, Marianne Sarrantonio of the Univ. of ME will make a field visit during the second harvest cycle of our study next year.  Our goals and objectives and outreach plan for this project remain relatively unchanged up to this point.

Objectives/Performance Targets

In 2016, after a successful prune (by fire), we successfully gathered useful data from the second of the prune cycles that this study encompasses (the first prune cycle was in 2014).  The data includes wild blueberry foliar analyses from each of our 16 test plots, as well as soil samples of each plot that were analyzed by two separate soil testing labs.

In March, we spread straw over the entire field (about 4 acres in total), spreading it evenly at a rate of 40 bales/acre.  Then on the first of May, we burned the field, setting the straw alight with a drip torch and containing the burn with a small crew using backpack water-pumps.  It was a good, even burn, which resulted in a very vigorous and healthy sprouting and regrowth over the summer.  It was a rather dry summer, with less than average rainfall, which may impact the size and number of buds set for next year’s harvest —we will just have to wait and see, and compare next summer’s yield data with this sort of natural phenomenon in mind.  It was quite apparent that the ramial chip mulch, that had been spread on most of our test plots (except the control plots) back at the beginning of the project in 2014, had begun to break down and disintegrate into the soil;  we are hopeful that this continuing decay means that the mulch will no longer hinder the physical act of harvesting next summer’s crop (as it did in 2014) and that perhaps it will not be tying up as many nutrients as one expects it does in the earlier stages of decomposition.

On July 12, when the new sprouts were in the “tip die-back” stage, we cut about 100 stems of the wild blueberry plants from each plot, as required by the Univ. of Maine testing service, which were then bagged and labeled and shipped to the lab.  The results (a nutrient analysis of the plants, which is used by wild blueberry growers for recommended soil amendments and fertilizing rates) were received in November.

In late September, we used our soil core sampling tool, and took two boxes of soil samples from each plot.  These boxes were labeled and then shipped (one sample from each plot) to two separate soil testing labs —one at the Univ. of Maine, the other one at Perry Agricultural Lab in Bowling Green, MO.  As we proposed in our original grant application, the standard soil test (Univ. of Maine) will give accurate pictures of the total nutrients present in the soil, while a Ream’s-type test (Perry Agricultural Lab) will give more a picture of what amounts of nutrients are readily available for the plant roots to take up, and checks both ammonia and nitrate nitrogens.  The results of these tests, including soil pH, Cation Exchange Capacity (CEC), and soil nutrient levels, were both received in early November.

All of this data has been gathered and analyzed, and now serve as the second set of data of foliar and soil nutrient levels which will be compared and contrasted to our pre-test baseline data (to be presented in our Final Report, next year).

Finally this year, we purchased a stainless steel hydraulic press, needed to extract juice from the wild blueberry plants for refractometer readings of their Brix level.  Due to the manufacturer’s (Pike Agri-Lab) delay in needing to construct and assemble the unit, we did not receive it until late summer —too late to do the weekly sampling and testing that we had intended and wanted to do from our proposal.  However, we trialed the unit and took a few sample readings, and are ready with it to conduct the research and collect the desired data next summer (and into the future after the current grant-funded research project is complete).

Accomplishments/Milestones

Several important relationships have been observed in the data that we collected this year, which suggest a positive direction in our study.  We are excited by the following results, and hopeful that they may produce positively related data in next summer’s harvest/yield and Brix readings of the fruit.

In 2016, we found that there were some significant measurable results between our control plots and the test plots where we had applied the ramial chip mulch plus the full-rates of fishmeal (70 lbs. N/acre) and aragonite (150 lbs. Ca/acre).  The positive relationships were observed in both the foliar analyses and the soil analyses.  The following list highlights the changes found in the mulch/full-rate fertilizer plots vs. our control plots:

     -slight increases (2 to 8%) in most of the major nutrients, as measured in the foliar tests, including Nitrogen, Calcium, Magnesium, and Phosphorus.

     -increase (7 to 10%) in some micronutrients, as measured in the foliar tests, including Boron and Zinc.

     -increase (3 to 20%) in the Cation Exchange Capacity (CEC), as measured in the soil tests, from both the Maine soil lab and Perry Ag lab.

     -significant increase (60 to 100%) in Calcium, as measured in the soil tests, from both the Maine soil lab and Perry Ag lab, observed in both lbs./acre and %saturation.

     -significant increase (37 to 39%) in Phosphorus, as measured in the soil tests, from both the Maine soil lab and Perry Ag lab, observed in lbs./acre.

     -significant increase (19 to 45%) in Magnesium, as measured in the soil tests, from both the Maine soil lab and Perry Ag lab, observed in both lbs./acre and %saturation.

     -significant decrease (43 to 47%) in Sulfur, as measured in the soil tests, from both the Maine soil lab and Perry Ag lab, observed in lbs./acre.

Other differences we found between the mulch/full-rate fertilizer plots and our control plots, which are not as clearly positive at this time, include the following:

     -slight increase (5 to 6%) in soil pH, as measured in the soil tests, from both the Maine soil lab and Perry Ag lab.

     -decrease (8 to 32%) in many micronutrients including Iron and Manganese, as measured in both the foliar tests and the soil tests from both the Maine soil lab and Perry Ag lab.

In general, we see that our fertilizer has effectively reached the plants and is available in the soil at higher rates in our mulch/full-rate fertilizer plots than in our control plots.  This will hopefully lead to higher yields in these fertilized plots, though next summer’s data will determine this.  We are also interested to find that the pH has increased in the mulch/full-rate fertilizer plots and that the Sulfur levels have gone down compared to our control plots, and will be reading about and researching these relationships over the next year, and considering their implications for future replication of this type of mulch/fertilizer process.  

Interestingly, there are no consistent relationships to be observed in this year’s data between the mulch only plots or the mulch/half-rate fertilizer plots and our control plots.  Again, this year’s nutrient-focused data will be most relevant to us only when analyzed further in relationship to next summer’s yield data, Brix readings, and then compared to our baseline data from the past.  Our final report, next year, will also include some budget analyses so that we can determine if any of our experiments are cost effective.

Impacts and Contributions/Outcomes

Collaborators: