Learning Series: What Your Weeds Are Telling You

Watch “What Your Weeds Are Telling You” with Kevin Elmy here:

Here is an audio version of “What Your Weeds Are Telling You” for listening on the go.

Here is the slide deck used by Kevin Elmy in his presentation, “What Your Weeds Are Telling You”.

Speaker Introduction: Kevin Elmy

Kevin Elmy is a Prairie farmer from eastern Saskatchewan and the author of Cover Cropping in Western Canada and Not Just Dirt. After selling his farm in 2021, he now focuses on consulting and coaching farmers on designing regenerative systems and thinking biologically about their operations.

Definition and Role of Weeds

A weed is defined as a plant growing where it is not wanted in agriculture. Weeds are nature’s response to soil conditions. Early successional plants produce many seeds due to their ecological role. Weeds aim to fix or change soil conditions, often indicating issues such as low diversity, salinity, compaction, or nutrient imbalances. Weeds have ecological advantages over crops, such as salinity tolerance, the ability to grow in anaerobic conditions, different root exudates, climate tolerance, and the ability to extract nutrients at low availability.

Recommended Resource

The book “When Weeds Talk” by Jay McCaman is recommended as a valuable resource for understanding why certain weeds grow and what their ecological advantages are. The book provides charts linking weed species to soil conditions and nutrient levels, helping farmers diagnose soil issues based on weed presence. For example, field bindweed indicates very low calcium and phosphate levels but high potassium and magnesium.

Soil Succession and Plant Succession

As soils progress from early to later successional stages, different plants appear or disappear.
For instance, weeds like pigweed and lamb’s quarters grow in soils with a fungal to bacterial ratio of 0.1 to 0.3, while trees prefer ratios above 10:1.

Managing Soil Biology to Control Weeds

It is really important to manage soil biology in order to control weeds. By increasing the fungal to bacterial ratio and soil organic matter, farmers can create conditions unfavorable for weeds. Strategies such as minimizing tillage, maintaining soil cover, increasing plant diversity, and incorporating livestock are viable options for balancing soil biology. These practices help build soil structure, improve nutrient cycling, and create an environment where desirable crops outcompete weeds.

Excess Soil Nitrates and Weed Growth

Excess soil nitrates are a major trigger for weed growth. Tillage stimulates bacteria, leading to rapid nitrogen mineralization and nitrate buildup. Maintaining living plants in the soil to tie up nitrogen and prevent weed germination is a great way to reduce soil nitrates. Cover crops, especially combinations of grasses, legumes, and forbs, were recommended to manage nitrogen levels and improve overall soil health.

Perennial Weeds and Soil Compaction

Perennial weeds often indicate soil compaction and anaerobic conditions, which are related to low calcium fluxes in the soil. Producers can improve calcium cycling and build soil structure to address these issues. It is recommended to use deep-rooted cover crops like radishes, chicory, and sweet clover to alleviate compaction and improve soil structure.

Rhizophagy Concept

Plants obtain nutrients by ingesting soil microbes through their root tips in a process known as rhizophagy. This process highlights the importance of soil microbiology and diversity for nutrient cycling. With proper soil biology management, most nutrients needed by plants are already present in the soil and can be made available through microbial activity.

Practical Applications

There are several practical applications that can be used to address weed concerns, including the use of alfalfa pellets as a calcium source and soil amendment. There are many benefits to diverse cover crop mixes as well as strategies for terminating cover crops without tillage.