Impact of Earthworm Castings On Apricot Tree Growth
Advisor: Karen Allendoerfer
Internship Location: Los Altos Heritage Orchard
Onsite Mentor: Dr. Jane Packard
I am doing a hands-on experiment at the Los Altos Heritage Orchard, where I am looking at the impact earthworm castings has on soil properties and on plant growth consequently. I am comparing the 12 tree earthworm castings applied group to the 12 tree non earthworm castings applied control group. I am measuring soil nutrient differences between the 2 groups in pH, Nitrogen, Phosphorus, and Potassium, and seeing how that is reflected by plant growth over time, seen in budding count, stem length, and chlorophyll content. This experiment should give me great insight into earthworm castings and how they may benefit apricot trees over traditional compost or other soil additives.
Project Blog
Post 1: Blog 1
For my senior project, I am looking at the impact of earthworm castings on apricot tree growth. I will be conducting an experiment where I am comparing 2 groups: a control (no earthworm castings to 14 trees) and an experimental group (earthworm castings applied to 14 trees) to see if the inclusion of this soil amendment makes significant differences in soil metric and plant growth consequently between the 2 groups. My research question is what effect would Earthworm Castings application have on apricot soil nutrient content, soil characteristics, and plant growth consequently. My hypothesis is that if Earthworm Castings is applied, the soil should see a clear increase in key plant nutrients and plant growth in comparison to the Control plots. As someone passionate about environmental sciences, I chose this project and to work with earthworm castings because it aligns with sustainable agriculture in how earthworm waste can be used in an organic manner to sustain plants. In the short term, If the results are promising, I would do further research to isolate the role of specific nutrients on plant growth. In the long term, the overall results will inform me of a better design of chemical solutions or products that can be applied to plants to increase agricultural productivity in an effective and efficient manner from a sustainability and economic standpoint
Post 2: Blog 2
This project is an experiment as I am seeing the effect of manipulated treatments on the response variables. In this experiment, I am comparing apricot trees exposed and not exposed to earthworm castings. 14 apricot trees are used in each group, totaling 28 apricot trees. All trees have been controlled for as they all have compost and the same drip irrigation system. Every 5 weeks, I will analyze soil and plant growth metrics between the 2 groups. For soil metrics, I will assess nutrient content of the soil. I will do this by using online test kits and sending my soil to Labs to get an accurate understanding of Nitrogen, Phosphorus, Potassium, etc. levels in the soil. I will also conduct water retention and soil profile analysis tests. For plant growth, I will look at budding count, number of fruits that develop on the trees, and stem length. Additionally, I will use leaves (leaf extracts coupled with paper chromatography) to assess the chlorophyll content off the trees and differences between the 2 groups. The goal of this project is to gather a lot of data to track over time in these 5 week periods to see if earthworm casting application has significant effects on soil and plant metrics of these trees.
Post 3: Blog 3
I started with Cycle 1, 5 weeks after the earthworm castings were applied and the groups were set. I had 2 Ziploc bags: Experimental and Control. I went to each of the 14 trees for each group and collected soil at about 2 feet in depth using a soil probe and placed it into the respective bags. After leaving the soil samples in the fridge for 1 day, I kept a portion of the soil for may home test with the Rapitest Soil Kit and sent the rest to A&L Laboratories. Here are the results from the Rapitest Soil Kit for Cycle 1: Control Group: PH – 6.5, Nitrogen – N1 – Deficient, Phosphorus – P3 – Sufficient, Potassium – K2 – Adequate. Experimental Group: PH – 6.5 – 7, Nitrogen – N1 – Deficient, Phosphorus – P4 – Surplus, Potassium – K2 – Adequate. In addition to measurements on soil, I looked at plant metrics, specifically the budding count, to see the development of the apricot trees 5 weeks after treatment application: Control group: 100 buds. Experimental group: 155 buds.
Post 4: Blog 4
I received the results on my baseline and cycle 1 soil samples from A&L Labs. The Lab reported the levels of many elements, salinity levels, organic matter percentage, cation exchange capacity, and pH. I made and attached some graphs to break down the results, but I will go over some of the biggest takeaways: When comparing the Control group baseline to after 5 weeks, there were slight increases in phosphorus and potassium levels, a decrease in nitrogen, and a decrease in pH. When comparing the Experimental group baseline to after 5 weeks, there were slight increases in phosphorus, potassium, and nitrogen levels and a decrease in pH. When ultimately comparing the Control group to Experimental after 5 weeks, the experimental group showed an increase in nitrogen and potassium levels, though there was a similar increase in phosphorus and a similar decrease in pH.
Post 5: Blog 5
5 weeks after Cycle 1, Cycle 2 began. The apricot trees started to grow leaves, and baby apricots were starting to develop. I counted 19 apricots in total among the Experimental Group and 23 apricots among the Control Group. This finding was not expected or aligned with my hypothesis that earthworm worm casting application would see more growth and fruit development in the experimental group than in the control group. As usual with each Cycle, I collected soil for each group to fill 2 1 gallon Ziplock bags using a soil probe. I have sent in the soil samples to A&L Laboratories and expect results shortly. I have attached pictures of what I am seeing at the orchard.
Post 6: Blog 6
I received the chemical analysis for the soil sent to A&L Labs. For the Control group, the readings looked similar to the original baseline, showing virtually no change in the elemental contents of the soil. However, for the Experimental group, there was an increase in levels of these nutrients such as N, K, Mg, and Ca. When comparing within the 2 cycles, the experimental group generally shows higher amounts of nutrient content than the control group and there is a more profound difference in Calcium, and earthworm castings application may play a role in that. My next step will be to do a paired t test using the within cycles values to see if the differences are significant. I have attached the graphs here for reference.
Post 7: Blog 7
5 weeks after Cycle 2, Cycle 3 began. The apricot trees were becoming much more defined and more fruit was starting to develop. As usual with each Cycle, I collected soil for each group to fill 2 1 gallon Ziplock bags using a soil probe. I have sent in the soil samples to A&L Laboratories and expect results shortly. I looked at the red tips, a sign of plant growth, for each tree in the 2 groups. In total, the experimental group had a higher total count in these red tips than the control group.
Post 8: Blog 8
I took my baseline, Cycle 1, and Cycle 2 data and made a new graph showing percentage changes in each period for the 2 groups for all 12 elements, shown below. This table showed that there were great fluctuations for each nutrient between periods for both Control and Experimental group, highlighting the complex nature of plants and nutrient contents in soil. Percent increases were seen with S and Mn while percent decreases were generally seen with Na and Cu.
Control | Exp.
Change from B to C1 | Change from B to C2 | Change from C1 to C2 | Change from B to C1 | Change from B to C2 | Change from C1 to C2
N | -84.62 | -15.38 | 450 | -95 | -36.67 | 1166.67
P | 9.09 | -2.27 | -10.42 | -29.33 | -34 | -6.6
K | 51.63 | 42.81 | -5.82 | 51.47 | 116.76 | 43.11
Mg | 4.87 | -6.6 | -10.94 | -16.42 | -4.75 | 13.96
Ca | 13.89 | 4.17 | -8.54 | 1.79 | 8.93 | 7.02
Na | -15.89 | -44.37 | -33.86 | -58.9 | -66.21 | -17.78
S | 213.64 | 95.45 | -37.68 | 144.12 | 20.59 | -50.6
Zn | 22.22 | 33.33 | 9.09 | 20 | 20 | 0
Mn | 257.14 | 80.95 | -49.33 | 147.83 | 65.22 | -33.33
Fe | 6.9 | -2.3 | -8.6 | 7.06 | -16.47 | -21.98
Cu | -4 | -16 | -12.5 | -23.08 | -30.77 | -10
B | 0 | 0 | 0 | 50 | 25 | -16.67
Post 9: Blog 9
I conducted statistical tests of significance to assess if the differences I was seeing between my 2 groups were potentially due to the earthworm castings and not chance alone. For each element for each of the 2 groups, I got the mean and standard deviation of n=3 values (Baseline, Cycle 1, and Cycle 2). I then did a 2 sample t test with my null Hypothesis not equaling my alternate Hypothesis. Here are the p values:
N: 0.20
P: 0.16
K: 0.31
Mg: 0.21
Ca: 0.03
Na: 0.88
S: 0.66
Zn: 0.0045
Mn: 0.75
Fe: 0.34
Cu: 0.43
B: 0.98
Both Ca and Zn's p values are below the significance level 0.05 indicating that there is convincing evidence that the presence of earthworm castings may result in this difference in these elements between the Control and Experimental groups.