Are pesticides sustainable?

All about the weeds..

Scientists demonstrated that the most weed infestations tend to develop in rain-fed cropland, which make up 80% of the world cropland. Farmers have to apply large quantities of herbicides in order to control such infestations and to maximize the crop yield but they could be inadvertently be affecting the soil conditions. 

When weeds are left in the field after harvest they decompose and become primary input components of the total system influencing its productivity. The input of nutrients from the weeds could be affecting the dynamics of soil chemistry and the micriobiotic biomass, which mainly consists of bacteria and fungi. 

Hence, removing such weeds in the first place could lead to increased competition over scarcer nutrient availability and lack of resources.

Pratibha Singh found that in soybean fields there is a positive correlation between the total yield of crops and the amount of fungi and bacteria found in the soil. This could be due to the fact that such organisms are a source of nutrients for the soy bean, which extracts nitrogen and minerals from the microbial biomass. 

If plant productivity is to be sustained – in order to maintain high yield crops – it is important that management practices take into consideration reducing the amounts of herbicides and maintain a certain level of weeds.

In an habitat with relatively high levels of weeds the organisms in the soil are more likely to grow faster increasing soil fertility and ultimately crop yield.

To further understand the impact of herbicides on local ecosystems and organisms I will look at a case study presented by Zhang in one of his recent studies in the Northeastern China Plain.

Herbicides in soybean agriculture

The China plain is one of the main agricultural areas in central asia and vast amounts of Imazethapyr - a selective herbicide - are used every year to suppress weeds infestations across the soybean fields. 

Studies have estimated that up to 6000tons of Imazethapyr are applied to soils in this area every year leading to critical implications for the local environment. In fact, pesticides are proven to be toxic to a variety of plants and not necessarily just the ones that they are meant to target.

Zhang carried out a study in order to assess how this herbicide influenced the local microbial biomass and affected changes over time. He proceeded by applying this chemical into three different soil samples and analyzing the different results over two years. He didn’t apply the pesticide in one sample and maintained it as a control variable, leaving the chemical in the other two samples for respectively 1 and 2 years. 

The effect of imazethapyr on soil microbes in soybean fields in northeast China

The results clearly highlight that the pesticide changed the composition of the microbial biomass community, leading to a shift in presence of fungi and bacteria species. As the chemical properties of the soil changed, the microflora was subject to higher levels of stress which could have affected the productivity levels and in turn increased competition amongst organisms leading to a reduction in the abundance of populations.

In conclusion, herbicides can bring about negative implications for the soil ecology in soybean cropland. This is not only worrying in terms of conservation but most importantly in terms of crop yield. When herbicides are applied, the total productivity of crops can be compromised as fungi and bacteria decrease in numbers leading to lower levels in nutrients in the soil.

Farmers can’t afford to loose crops to weed infestation but by applying herbicides they could be compromising the sustainability of agricultural practices in their region. 

Could genetically modified crops that are resistant to plagues be a more sustainable answer to this issue?

 Stay tuned for further discussions and feel free to leave a comment below!