Curly dock (Rumex crispus) is an invasive plant species found throughout the United States in pasture land and hay fields. In general, this aggressive plant can grow up to five feet tall, block sunlight to the native plants and out-compete other plants for essential nutrients in the soil. Curly dock thrives in localized portions of several pasture areas at Earth Be Glad Farm, a certified organic farm in Lewiston, Minnesota. In organic farming practices, soil plays a vital role in naturally suppressing weeds. This study was conducted to determine soil conditions (including nutrient concentration and availability, and physical properties such as soil texture and compaction) that foster the growth of curly dock in certain pasture areas, and will potentially guide soil management practices to restore the farm’s pasture areas. Fifteen samples were collected in three transects; two within extensive curly dock growth, and the third as a control in a grazing area with no curly dock growth.
Nutrient availability was determined through cation exchange capacity (CEC) experiments and through testing with a LaMotte STH-14 professional soil testing kit. Concentrations of calcium, magnesium, sodium, potassium, aluminum, iron and manganese in the CEC extracts were determined by atomic absorption spectrometry. The soil test kit employs colorimetric methods for the semi-quantitative determination of a variety of elements, including nitrogen, potassium, phosphorus, magnesium, calcium, sulfate, aluminum, iron and manganese. Total concentration of most of these elements in the samples was determined by digestion followed by analysis on inductively coupled plasma-optical emission spectrometry at an outside laboratory.
In organic farms that depend upon practices such as crop rotation to lower the spread of weeds and increase accumulation of organic matter, farmers rely heavily on the fertility of the soil to increase crop production. Results of this study, including differences in soil fertility and preferential growth conditions of curly dock, may help guide changes in soil management practices at the farm.