Soil and Plant Nutrition and its Affect on Giant Ragweed Growth and Proliferation

With the uncertainty of government funding we waited until we had the funds in hand before buying the supplies to begin the research. This ultimately led to a delay in getting the very first soil and sap samples taken and the overall structure of the research trial shifting slightly.

The original research proposal outlined 5 locations within a field where testing would take place, replicated over 3 fields. Sap samples were to be collected from: Weeds with treatment, weeds without treatment. Cash crop among weeds with treatment, and without, and a cash crop sample from a clean area of the field.

The theory was that strategic foliar applications might slow down the weeds ands stunt their growth. However, because the start of the research was delayed, the weeds were well established by the time the sample results were back and an application could be made.

Within a few weeks the weeds quickly shaded out the cash crop affecting the results of future leaf samples. By the end of the growing season the giant rag weed was +10ft tall and in some places the cash crop beneath had long died out from lack of sunshine. 

However, we were still able to collect valuable data!

By the middle of year 1 we pivoted to focus primarily on gathering data on what nutrients the giant ragweed was concentrating compared to the cash crop and forego doing different treatments until year 2. This allowed us to increase the number of fields that were sampled and increase the variety and robustness of the data.

From the 6 field systems that were sampled we compared the ragweed nutrient concentrations with those of the cash crops (organic corn, organic soybeans, and organic cover crop sunflowers). Across all of the fields a handful of nutritional differences between the cash crop and the ragweed became apparent.

In year 2 we will focus on collecting a few more sap samples as well as soil samples at the time of weed germination to compare soil fertility levels with sap samples. First, we will again test giant ragweed leaves for nutrient uptake with a goal of focusing on younger growth stages. These leaf results will be compared with soil tests taken in the spring to evaluate if the weeds are accumulating nutrients that show up low on soil tests from the same location. (This relates to an original hypothesis of this study.) Next, taking the information gathered from year 1, we will see if "overloading" the newly emerged weeds with certain nutrients through foliar sprays can slow or stop giant ragweed growth. We will target the nutrients noted in our samples over the growing season of year 1, and may adjust later foliar applications based on any additional findings in the early soil and leaf testing done in year 2.