Weed management is an important part of crop production, but how does the no-till farmer keep weeds under control without conventional farming methods at his disposal?
Richard Findlay from the No-till Club of KwaZulu-Natal says no-till farming requires a complete mind shift. The challenge is to overcome the first years of changing from conventional farming to no-tillage.
Also read: Getting started with no-till
This includes dealing with weeds on the land. If farmers adopt a holistic approach to weed control, they can reduce weed populations and improve soil health and crop performance simultaneously.
THE DIFFERENCE IS IN THE METHOD
- Tilling, which is the agricultural preparation of soil by ploughing, ripping or turning it, has always been used to control weeds and produce a clean seedbed.
- Turning the soil to destroy weeds and prepare seedbeds leads to a bare soil surface with a higher risk for soil erosion.
- When soil is turned, carbon dioxide is released, causing a reduction of carbon in the soil. Carbon is essential because it forms the basis of chemical, physical and biological processes in the soil.
- The difference with no-till is that weed control by these means is eliminated.
- Instead, farmers plant cover crops and increase planting density.
- They also make use of crop rotation and herbicide-spray programmes to control weeds.
- Farmers who want to make the switch to no-till must follow a comprehensive weed-control strategy and integrate as many weed management options as possible.
Also read: No-till and perfect seed placement
HOW IT WORKS
“When converting from conventional farming methods to no-till, farmers have to become accustomed to seedbeds that do not look perfect. At first, beds won’t look as even and clean as conventionally-prepared beds,” Findlay says. However, over time farmers won’t notice much difference.
He recommends that farmers starting out with no-till should convert no more than a quarter of the farm initially. If you go about it this way, you use less mechanical input each season, combined with the recommended ground preparation.
Effective weed control is possible in the no-till environment.
In Argentina, where no-till farming is widely used, a plot of land that has been farmed using no-till principles for 25 years has no weeds at all. Although farmers won’t necessarily have to wait such a long time to start seeing results, they should focus on improving soil heath.
“The aim of conservation farming is to improve soil structure. We have even seen that earthworms are returning to soil on our farms that we have worked with no-till practices.”
ROW SPACING AND CROP DENSITY
- Adopting a much tighter row spacing when planting is a good means of weed control.
- Rows that are spaced closer together, coupled with a higher crop density, means that a plant canopy will form much more quickly.
- A high crop density improves the crop’s ability to compete with weeds.
- It also shields the land from sunlight, which encourages weeds to grow.
- Farmers should also control weeds in the early growth stages before they start producing seed.
- “A canopy is natural and is the best way to get rid of weeds.”
Cover crops, also known as green manure, form a canopy on the soil to suppress weed growth.
Perennial grasses (Imperata cylindrica, Cynodon dactylon) and other problem weeds such as Striga species or Chromolaena odorata can be reduced by 1 or 2 seasons of using cover crops.
Some cover-crop species have allelopathic effects (they release a toxin that suppresses the growth of nearby competing plants), which make them even more efficient at weed control. For example, black oats is frequently used in Brazil for this purpose.
According to the Federation of No-till Associations in Brazil, research conducted in that country has shown that black oats used as a green manure cover crop before planting soya beans can increase their yield by as much as 63%, as compared to soya beans after wheat.
One of the main lessons learnt in no-till systems is that farmers should, if possible, never leave the land fallow.
Studies show that fallow periods of only a few weeks will cause an increase in weeds, seeding of weeds, reduction of soil cover and soil erosion.
Farmers should rather plant a cover crop immediately or as soon as possible after harvesting the previous crop.
“Many farmers want to their lands to be aesthetically perfect, but farming sustainability should be more important.”
- Cover crops also protect the soil, allow for better moisture retention and create a better habitat for beneficial insects to inhabit the soil.
- Farmers should find out which cover crop will be suitable for their area.
- Also keep in mind that cover crops will vary depending on whether the land is irrigated or dryland.
- In windy areas, farmers often use cover crops to anchor the soil to prevent it from blowing away in severe windy conditions.
- Farmers have also found that cover crops help them to obtain higher yields. In terms of inputs, it may cost a bit more to plant cover crops but an increase in yield is good compensation.
CHEMICAL WEED CONTROL
The use of chemical weed control in conservation farming is necessary, in combination with other weed-management methods. It is a method of farming that helps farmers to conserve, improve and make more efficient use of their natural resources.
“No-till is not organic farming. It is a form of conservation farming.”
The United Nations Food and Agriculture Organisation (FAO) also makes a clear distinction between conservation farming and organic farming.
Although both types of farming are based on natural processes, conservation agriculture does not exclude the use of chemical inputs. The FAO says herbicides are an important component, particularly in the transition phase, until a new balance in the weed population is achieved.
Generally however, conservation agriculture farmers use fewer chemical inputs than conventional farmers.
- This article was written by Wilma den Hartigh and first appeared in Farming SA.