Effects of Plastic Mulch, Wood-Shaving Mulch, Manual Weeding and Legume Intercropping on Weed Suppression, Rhizosphere Enzyme Activity and Maize (Zea mays L) Performance in Buea, Cameroon

In the humid, rain-fed fields of Cameroon, maize is a lifeline. It is the third most consumed cereal in the world, and for many families in this region, it is the foundation of their daily diet. Yet, the harvest is often disappointing. Small-scale farmers struggle to grow more than a few tons per hectare, a fraction of what the crop could produce under ideal conditions. One of the biggest enemies to this potential is the weed. These unwanted plants compete fiercely with maize for sunlight, water, and nutrients, especially when the corn is young and vulnerable. If left unchecked, weeds can slash the grain yield by half. For decades, farmers have relied on manual hand-weeding, a back-breaking task that is becoming harder as labor becomes scarce and expensive. Chemical herbicides offer a faster solution, but they bring their own problems, including resistant weeds and soil degradation. This creates a pressing need for farming methods that are gentle on the land but tough on weeds, keeping the soil healthy while protecting the crop.

To find a better way forward, a team of researchers at the University of Buea set up a field experiment in the town of Buea, located in Cameroon's humid forest zone. They wanted to test whether specific, low-tech farming practices could outperform the traditional method of simply letting weeds grow or the standard practice of manual weeding. The team established a series of plots, each measuring four meters by four meters, and applied five different treatments to see how they would affect the weeds, the soil's hidden biological life, and the final maize harvest. The treatments included a control group where no weed control was applied, a group where weeds were removed by hand, a group covered with a layer of wood shavings, a group covered with black plastic sheeting, and a group where maize was planted alongside groundnuts. The goal was to see if covering the soil or planting a companion crop could suppress weeds naturally and improve the biological health of the ground beneath the maize.

The results showed that covering the soil or planting a companion crop worked remarkably well at stopping weeds. In the plots covered with black plastic mulch, the weed community was completely silenced; no weeds emerged at all. The plots where maize was intercropped with groundnuts also saw weeds disappear entirely by the eighth week after planting. Even the wood shavings, which acted as a physical barrier, significantly reduced the amount of weed growth compared to the untreated plots. In contrast, the plots where farmers relied on manual weeding or did nothing at all still had a heavy presence of weeds, though the manual weeding plots saw a drop in weed numbers after the second round of weeding. The researchers found that the untreated control plots maintained the highest number of different weed species, while the plastic mulch and intercropping plots effectively eliminated the weed community.

Beyond just keeping the weeds away, the different treatments changed the biological activity within the soil. The researchers measured two key indicators of soil health: the amount of nitrogen held by soil microbes and the activity of an enzyme called acid phosphatase, which helps plants access nutrients. The plots with intercropped groundnuts and the plots covered with wood shavings showed a dramatic boost in these biological markers. The intercropping treatment increased the potential activity of the acid phosphatase enzyme by seventy-five percent compared to the control, and it boosted the microbial biomass nitrogen by a similar margin. The wood shavings also performed well, increasing these biological activities by about fifty to sixty percent. This suggests that the decomposition of the wood and the presence of the groundnut roots stimulated the soil's microscopic life, making the soil more fertile and active. Interestingly, the plastic mulch and the manual weeding treatments did not show the same level of improvement in these specific biological indicators, with some even showing lower microbial activity than the untreated control.

When it came to the final harvest, the story was a mix of clear gains and subtle differences. The researchers measured the weight of a thousand maize grains to determine the size and quality of the kernels. Here, the intercropping and plastic mulch treatments shone, producing the heaviest grains. The intercropped maize grains weighed 380 grams per thousand, and the plastic mulch grains weighed 360 grams, both significantly heavier than the 230 grams found in the control and wood shaving plots. This increase in grain weight suggests that the plants in these treatments were better able to fill their kernels, likely due to better moisture retention from the plastic or improved nitrogen availability from the groundnuts. However, when the researchers calculated the total grain yield per hectare, the differences between the treatments were not statistically significant. The intercropping plots produced the highest numerical yield at five tons per hectare, followed by the plastic mulch at 4.5 tons, but the variation was not large enough to be considered a definitive statistical victory over the other methods.

The study also revealed a strong link between the amount of weed growth and the final harvest. The researchers found that as the dry weight of the weeds increased, the maize grain yield decreased. This negative relationship confirms that the competition for resources is real and damaging. The plots with the most weeds produced the least grain, while the plots where weeds were suppressed produced more. The wood shavings, which acted as a mulch, reduced weed growth effectively in the early weeks, but the plastic mulch and intercropping were superior at maintaining a weed-free environment throughout the season. The researchers noted that the wood shavings were effective at blocking sunlight and physically preventing weeds from emerging, while the groundnut cover quickly spread across the soil, crowding out any potential weed growth.

Despite these promising results, the authors caution that the findings are based on a single season of data. They measured the soil biological indicators at only one point in time, without a baseline measurement from before the treatments began. This means that while the data strongly suggests that mulching and intercropping improve soil biology and suppress weeds, the long-term effects on the soil and the consistency of the yield benefits across multiple years remain to be seen. The study did not measure the specific mechanisms of how the groundnut improved nitrogen or how the plastic retained heat, leaving some questions about the exact "why" behind the success. Nevertheless, the evidence points toward a viable path for smallholder farmers in sub-Saharan Africa. By integrating groundnut intercropping, plastic mulch, or wood shavings into their maize farming, they can simultaneously tackle the problem of weeds and enhance the biological quality of their soil, offering a sustainable way to intensify production without relying heavily on chemicals or exhausting labor.