Using invasive Eurasian milfoil as an organic soil amendment: Effect on tomato yield

Using invasive Eurasian milfoil as an organic soil amendment: Effect on tomato yield

Summary

The “Using Invasive Eurasian Milfoil as an Organic Soil Amendment: Effect on Yield of Tomato Crop” project aimed to identify the effect of low and high does treatments of Eurasian Milfoil on tomato yields as compared to a control group. Brittany Harris (Coordinator) carefully managed the measurement of tomato yield throughout the growing season, and Amy Ivy (technical advisor), aided in experimental design and oversight, and took foliar and soil tests. 

We learned that milfoil is not available until June, when temperatures rise in the Northeast and milfoil grows in the lakes.  The tomatoes are transplanted into the greenhouse in April, so we were not able to work the milfoil into the soil as planned. Instead, we applied the milfoil as a mulch around the tomato plants and placed drip irrigation on top of the milfoil to see if any nutrient would be added to the soil that could in turn increase tomato yields. 

Objectives/Performance Targets

In a randomized block experiment in a 96” by 24” high tunnel, we created 12 experimental blocks (each measuring 20” by 3”), and randomly assigned one of 3 treatments to each block. The treatments were applied as a mulch. The treatments were, (1) high dose of Eurasian milfoil; 10 gallons of moist milfoil per 60ft^2 block, (2) low dose of Eurasian milfoil; 5 gallons of moist milfoil per 60ft^2 block, or (3) control; no milfoil applied.

We then carefully measured yield of the 15-20 plants in the middle of each block all season long. Yields were not significantly different between high dose, low does, and control groups. We believe this is due to the way the milfoil was applied, as a mulch instead of as a soil amendment. In the past, we have experienced anecdotal evidence of success with milfoil used as part of our composting system. We believe that the beneficial nutrients from milfoil (if any) was not available for uptake by the plants in the way it was applied. In the future we would like to study milfoil’s effect on the soil, rather than on its source as a nutrient, but that will be another experiment entirely. Outreach efforts still need to be completed at this time.

• Effect of Milfoil Treatment on Tomato Yield

Accomplishments/Milestones

The milfoil applied as mulch provided little nutrient value to summer crop of high tunnel tomatoes. It did not increase yield; in fact the control plots had a higher overall yield than either of the two treatments. Foliar nutrients level were lower August after the milfoil application than in June before the application, but that is to be expected since August is the period of maximum fruit load and nutrient use by the crop.

The time of application of the milfoil was not ideal in terms of providing a nutrient benefit. Tomatoes need to be planted in late April-early May but milfoil is not available until June. The supply was limited this year, with only one application possible. The foliar nutrient levels were statistically the same between the 3 treatments, indicating that the milfoil did not have an effect.

Tests conducted:

6/20/14 – pre milfoil application foliar nutrient analysis of 4 quadrants of study area

8/10/14 – post application foliar nutrient analysis of each of the 12 treatments

11/24/14 – dry sample of milfoil foliar nutrient analysis

Impacts and Contributions/Outcomes

Growers who have added milfoil to their compost or worked into the soil before planting feel it has a benefit. To study this more fully milfoil will need to be stockpiled in advance and then worked into the soil in significant amounts before planting in a replicated trial to see if it enhances root growth and therefore plant growth. It may well be that the key benefit milfoil provides is as a renewable source of organic matter to improve soil health. This could be a significant benefit and further study to determine optimum rates would be very useful.

Collaborators: