Effects of non-NPK organic soil amendments on yield and quality of vegetable crops
For organic growers, there are now numerous soil amendments on the market that do not contain significant quantities of recognized necessary plant nutrients. Despite the fact that such amendments do not provide any primary nutrients (nitrogen, phosphorus, potassium–NPK), they continue to be employed by many farmers who believe that these amendments have alternative benefits. As one of the leading soil amendment retailers in the Northeast, Fedco Organic Growers Supply wanted to determine whether some of its best-selling amendments had any significant effect on crop yield or Brix content (a measure of soluble solids, which relates to flavor and nutrient density). We chose yield and Brix as our two metrics because those seemed like they would be two of the most important metrics for market growers, but please note that there are other important metrics we didn’t use, such as cation exchange capacity (CEC), soil porosity, and soil life. The chose to test these amendments on two crops: spinach and potatoes.
Due to severe drought conditions, the 2016 growing season was particularly challenging for farms in central Maine. Of course, farmers did not know this ahead of time, so they planted their spring crops how they always do, and for many this meant planting without an irrigation system in place, since spring in Maine usually comes with ample rainfall. Due to the drought (and unseasonably high temperatures in the spring), two of the four cooperating farms in our study experienced complete crop failure on both their spinach and potatoes, which severely compromised our study. Thankfully we got useable data from both of the remaining cooperating farms.
By mid-August, we had all the data from the harvest. We performed statistical analysis tests, to determine how the crops performed with each amendment, compared to the control. So far, we have presented the results of this study at two events, NOFA’s 2016 Summer Conference, and MOFGA’s 2016 Common Ground Country Fair.
We tested the hypothesis that Azomite, BrixBlend Basalt, biochar, Menefee humates, and zeolites have a significant positive impact on crop yield and quality.
Four certified organic farms participated in this study. Every farm grew both spinach and potatoes with the same space allocated to each plot. At each farm, there were 4 replicates of each amendment-crop combination. Each replicate plot was sized at 3’ x 5’ (15 sq ft), there were 6 total treatments (5 amendments and 1 control), and 4 replicates of each treatment. Once these areas were designated at each farm, every farmer submitted soil samples to the University of Maine Soil Testing Service. Based on the soil test results, each farm was given customized bags of NPK fertilizer (each paired with a specified amendment). The goal was to ensure that the amounts of available N, P, and K were roughly equal across all four farms. The goal was to achieve–at every farm–the following N-P-K levels: 85-40-150 (lbs/acre) for spinach, and 180-50-450 for potatoes. Application rates for the non-NPK amendments (the amendments being tested) were determined by industry averages. Farmers applied fertilizer + amendments as instructed, and planted their crops according to my specifications. We diverged from the original plan of direct-seeding the spinach: we had every farmer use transplants instead.
As noted above, two of the four farms experienced crop failure on their spinach and potatoes. With the two remaining farms, we proceeded with the harvests and taking measure. Spinach harvests were determined by the farmers based on leaf size and timing of markets. Potatoes were harvested when the plants had died back sufficiently, by mid-August. We made numerous attempts to measure the Brix of juice we extracted from spinach leaves and potato tubers, but the refractometers we had were not adequate for this purpose. No matter how we treated the juice, the refractometer readings were always blurry and thus not scientifically useful. Apparently, the only way to gather useable Brix data is to use an expensive digital refractometer, which was not written into our budget proposal. On the other hand, weight data from the two farms was sound, complete, precise, and scientifically useful.
With the yield (weight) data, we performed statistical analysis tests–specifically, paired t-tests–that compared each amendment to the control, in order to determine if there were any significant differences. We originally thought we would use one-way ANOVA tests, but once we had all the data, it became clear that paired t-tests were much more appropriate.
Proposed work plan and delivery:
Feb 21. Distribute project packages to cooperating farmers: A project package was delivered to each of the 4 cooperating farms.
April 4. Farmers conduct pre-fertilization soil tests. May be slightly earlier or later depending on when soil thaws: Each of the 4 cooperating farms sent soil samples to University of Maine Soil Testing Service. Soil test results were emailed to me, the project organizer. I used these results to make a customized N-P-K blend for each farm (in order to standardize the N-P-K levels across all 4 farms).
April 21. Project organizer distributes NPK fertilizers to each farm: NPK fertilizers were distributed (along with the non-NPK amendments being tested).
April 21-May 1. Farmers till in NPK fertilizers and non-NPK amendments being tested: All 4 farms tilled in fertilizers and amendments.
May 1. Farmers conduct post-fertilization soil tests and notify project organizer. Farmers plant spinach: Farmers conducted post-fertilization tests and planted spinach.
May 9. Organizer distributes potatoes to farmers: I distributed potatoes to them.
May 21. Farmers thin spinach: Since we decided to have all farms transplant the spinach instead of direct seed, thinning was not necessary.
May 28. Farmers plant potatoes: Farmers planted potatoes.
June 7. Organizer contacts farmers to schedule first spinach harvest: I was in touch with farmers to determine when their first harvest would be.
Week of June 15. Farmers’ first spinach harvest, attended by project organizer. Brix and yield measurement taken: The first spinach harvest happened at 2 of the 4 farms (due to heat and drought, two farms had crop failure before the spinach got to a harvestable stage). Yield data collected successfully, but there were complications with measuring Brix (see explanation in OBJECTIVES/PERFORMANCE TARGETS above).
Week of June 21. 2nd spinach harvest: The 2 remaining farms had a successful spinach harvest.
Week of July 1. 3rd spinach harvest: Only 1 of the 2 remaining farms had enough spinach grow back for a 3rd harvest. The other farm’s spinach had bolted completely.
Week of July 7. 4th spinach harvest, if needed: There was a successful 4th harvest at the one farm whose spinach had not yet bolted.
July 10. Farmers send all spinach yield and brix data to project organizer: Farmers sent yield data to me. Regarding brix data, see above.
July 12-14. Organizer enters spinach data into spreadsheet. 3 hrs/day, 9 hrs total: Data entry successful, though there was only data from 2 farms.
July 19-21. Organizer performs statistical tests for spinach data. 3 hrs/day, 9 hrs total: Statistical tests successful. At this point in the study, it became clear that it would not be scientifically meaningful to use data from 2 farms in the same statistical test, because the environmental variables at farm 1 were dramatically different from the environmental variables at farm 2.
For the primary data analysis, I performed statistical tests using data from only one farm at a time (comparing the performance of each amendment to the control at that farm).
I did perform statistical tests on the aggregate data as well (using data from both farms in the same test), and I included those in the Impact and Contributions/Outcomes section, but these test results should be considered less meaningful compared to the primary data analysis I described in the paragraph above.
July 21. Organizer contacts MOFGA, NOFA, and UMaine to arrange publicization of study: We had already scheduled ourselves to present at NOFA’s Summer Conference and MOFGA’s Common Ground Fair, because the organizers for those two events needed to schedule us well in advance. Because we had 2 of our 4 cooperating farms drop out of the study due to crop failure (and because of this season’s severe drought), we decided to postpone scheduling any more presentations for the calendar year. Our reasoning was: though we could certainly present about how we conceived of the study and how we designed & executed the study, we didn’t get enough data to draw any conclusions about how the amendments affected yield and brix.
July 26-28. Organizer develops educational materials based on spinach results: 1) Special write-up for Fedco website, 2) PowerPoint Presentations for public events. 5 hrs/day, 15 hrs total: I developed educational materials to distribute via the Fedco newsletter–with the plan to publish a write-up for the Fedco website in the winter. I later worked on developing materials for live presentations.
Aug 12-14. Organizer presents spinach results at NOFA Summer Conference: Alice Percy–my supervisor–presented our preliminary results at this conference.
August 15. Organizer contacts farmers to schedule potato harvest. If necessary, potato foliage is flamed or mown to allow tubers to cure prior to harvest: This happened as planned.
August 22. Farmers harvest potatoes, with project organizer in attendance. Farmers clean, weigh, and measure brix levels within 1 week of harvest: Farmers were able to harvest, clean, and weigh potatoes as planned. Regarding brix measurements, see explanation above.
August 29. Farmers send all potato yield and brix data to project organizer: Farmers sent data to me as planned.
Sept 6-8. Organizer enters potato data into spreadsheet. 3 hours/day, 9 hours total: I entered data as planned.
Sept 13-15. Organizer performs statistical tests for potato data. 3 hours/day, 9 hours total: I performed statistical tests as planned.
Sept 20-22. Organizer develops educational materials based on potato results: 1) Special write-up for Fedco website, 2) PowerPoint Presentations for public events, and 3) one-page handout on results to offer those who attend our presentations. 3 hrs/day, 9 hrs total: I developed presentation and handout materials. Regarding the write-up for the Fedco website, see explanation for July 26-28 activity.
Sept 23-25. Organizer presents spinach and potato results at MOFGA’s Common Ground Country Fair: I presented about our project, which included a lengthy interpretation of our results.
October 15. Organizer presents results at Fedco’s Annual Bulb Sale: This event was not as well-attended like it usually is, so we did not present about the study.
Nov 5-7. Organizer presents results at MOFGA’s Farmer to Farmer Conference: The workshops/presentations at this event are all 3 hours long: 1.5 hours of the presenter having the floor, and then 1.5 hours of group discussion. We did not have enough material to present, given this year’s severe drought and the fact that two of our four farms dropped out of the study. We hope to present at a future Farmer to Farmer Conference, especially if we are awarded a grant for 2017-2018 to study the effect of these amendments on soil life.
Impacts and Contributions/Outcomes
Despite the obstacles we faced in the study this year (namely, severe drought & 2 of 4 farms having to drop out due to crop failure), we were able, nevertheless, to draw some preliminary conclusions. In every single statistical test that compared the yield of plots treated with a given amendment with the yield of the control plots, there was no statistically significant difference found.
Although we had a limited data set to work with, we could tell that no amendment was proving to be a “silver bullet” (i.e. an amendment that miraculously results in increased yield within the same season of application). That, alone, is a fairly important finding, because there are growers who purchase these non-NPK amendments and expect them to give them an immediate payback. That being said, some experts on the subject of non-NPK amendments–such as Dan Kittredge of the Bionutrient Food Association–point out that without ample soil moisture, such amendments cannot be expected to perform.
While crop yield and brix are very important to growers, they are not the only important considerations for sustainable agriculture, nor are they the only factors of the farm system that may be affected by the application of non-NPK amendments. For example, the use of non-NPK amendments may change certain characteristics of the soil, such as CEC, porosity, or the quantity & quality of soil microbes. We at Fedco have noticed recently that the farming community has become more interested in soil microbial life and how to improve it. As it so happens, of the five amendments we studied (Azomite, Biochar, BrixBlend Basalt, Menefee Humates, and Zeolites), each is said to promote beneficial microbe activity in some way.
We therefore have applied for a 2017-2018 SARE Partnership Grant to investigate how soil life may be influenced by these five amendments. For the study we proposed, we specifically chose to avoid using vegetable crops as the medium; instead, we opted to test the soil life in areas that were simply planted to a cover crop, so that the success of the plant growth wouldn’t be so dependent on water, and we chose a heat-loving cover crop (BMR Sorghum/Sudangrass) so that extraordinarily hot growing conditions wouldn’t be a problem. We very much look forward to doing further research with non-NPK amendments.
For the statistical test results from our 2016 study, see attachments.
AZOMITE potato, Aggregate AZOMITE potato, Crooked Door AZOMITE potato, Earth Dharma AZOMITE spinach, Aggregate AZOMITE spinach, Crooked Door AZOMITE spinach, Earth Dharma BASALT potato, Aggregate BASALT potato, Crooked Door BASALT potato, Earth Dharma BASALT spinach, Aggregate BASALT spinach, Crooked Door BASALT spinach, Earth Dharma BIOCHAR potato, Aggregate BIOCHAR potato, Crooked Door BIOCHAR potato, Earth Dharma BIOCHAR spinach, Aggregate BIOCHAR spinach, Crooked Door BIOCHAR spinach, Earth Dharma HUMATES potato, Aggregate HUMATES potato, Crooked Door HUMATES potato, Earth Dharma HUMATES spinach, Aggregate HUMATES spinach, Crooked Door HUMATES spinach, Earth Dharma ZEOLITES potato, Aggregate ZEOLITES potato, Crooked Door ZEOLITES potato, Earth Dharma ZEOLITES spinach, Aggregate ZEOLITES spinach, Crooked Door ZEOLITES spinach, Earth Dharma
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