Unanswered questions and unquestioned answers

Over the past few decades, Conservation Agriculture (CA) has moved from theory to practice for many farmers in southern Africa. CA is a system that involves minimum soil disturbance, crop residue retention, and crop diversification among other complimentary agricultural practices. One reason for its increasing popularity is its potential to mitigate threats from climate change while increasing yields.

However, there are limits to the adaptation of CA, especially for smallholder farmers. Challenges are both agronomic (e.g. lack of sufficient crop residues as mulch, weed control, pest and disease carryover through crop residues), socio-economic, and political (both locally and regionally).

A recent paper, Unanswered questions and unquestioned answers: the challenges of crop residue retention and weed control in Conservation Agriculture systems of southern Africa, published in the journal Renewable Agriculture and Food Systems in February 2024, led by CIMMYT and CGIAR scientists examines two specific challenges to more widespread CA adaptation: how to deal with trade-offs in using crop residue and finding alternatives to herbicides for weed control.

For crop residue, the two most prevalent actions are using leftover crop residue for soil cover or feeding it to livestock. Currently, many farmers allow livestock to graze on crop residue in the field, leading to overgrazing and insufficient ground cover. This tradeoff is further challenged by other multiple household uses of residues such as fuel and building material. The most common way to control weeds is the application of herbicides. However, inefficient and injudicious herbicide use poses a threat to human health and the environment, so the research team set out to identify potential alternatives to chemical weed control as the sole practices in CA systems.

“The answer to the question ‘how should farmers control weeds?’ has always been herbicides,” said lead author Christian Thierfelder, CIMMYT principal cropping systems agronomist. “But herbicides have many negative side effects, so we wanted to question that answer and examine other potential weed control methods.”