DO WE GAIN SOMETHING GOOD FROM STRAW BURNING?

It’s been a debate if we talk on post-harvest straw burning. It is a general knowledge if straw burning has the environmental risks, such as reducing air quality because it produces greenhouse gases and particulate matter and reduces visibility because of a combination of emitted air pollutants and fog. Poor visibility leads to increased traffic accidents. But do we gain something beneficial for burning straw?

Fire has been long known to use in agriculture. Why do farmers still burn considering the environmental risk? The answer is so much anticipated that it is economical and practical to remove straw as the most abundant agricultural harvest. Do we get more than that? Let’s take a look at more scientific facts on straw burning.

Fire can be used in organic farming to reduce the intensive use of chemicals, especially where the application of herbicides is needed to control weeds in pastures. Straw burning can be more effective in maintaining a low incidence of crown rot infestation. Crown rot is a wheat soil-borne disease that has become more prevalent as reduced tillage practices involving straw retention have been widely adopted. Additionally, in a study shows burning rice fields after harvesting eliminates straw and minimizes rice stem rot.  In terms of promoting biodiversity, fire-based wildland management was compared to organic farming, where both practices increase total organism abundance and evenness.

The effect of fire on vegetation and soil properties depends on fire severity. Light to moderate fire temperatures in some studies is beneficial in increasing soil nutrients. However, severe fires, such as wildfires, can cause the removal of soil organic matter, loss of nutrients, leaching and erosion, structure, and porosity degradation.

In the US, the use of fire for prescribed burning is regulated. Prescribed burning has been used to manage smoke hazards and public complaints of reduced visibility. Prescribed burning is defined as a burning activity set under planned conditions to achieve a specific management goal.  The state of Oklahoma has used the Oklahoma Mesonet providing “Fire Prescription Planner” https://www.mesonet.org/index.php/okfire/fire_rx specify the lower and the upper limits for various variables of weather, dispersion conditions, dead fuel moisture, and fire danger. This website helps people to decide bun or non-burn days. It is essential to pay attention to this fire weather since prescribed burning is risky because of the possibility of escaped fire. Most basic farm owner’s policies can cover legal liability aspects of prescribed burning. General policy limits range from $25,000 to $500,000.

Let’s compare straw burning with straw incorporation or retention. Straw incorporation or retention is indeed a non-chemical method to conserve soil nutrient reserves in the long term since the remaining stubble and straw incorporation returns most of the nutrients into the soil. Even though physical, chemical, and biological soil properties can be improved by this method, large quantities of un-weathered residues can cause residue toxicity. This method stimulates the phytotoxic substances that hinder the radicle growth of rice seedlings being released.

In non-inversion tillage systems, crop residue management can lead to reduced crop establishment. A study on crop residue incorporation for wheat suggests that crop establishment was mainly affected by the residue's position in relation to the crop seed.

In some environments, straw incorporation/retention can negatively affect crop production.

In N limiting environments, the method reduces N availability. Besides, in colder temperatures, retaining straw on the soil surface can lower soil temperature. In regions with high rainfall, excess soil moisture in this incorporation/retention can result in waterlogging. Conversely, in semi-arid areas with light rain, crop residues can intercept rainfall and increase evaporation.

Based on those facts, which one is better? Straw burning or straw incorporation/retention? As described above, straw burning is a risky management tool that reduces air quality, reduces visibility, and the risk of escaped fire. However, straw burning would remain an option with the benefit of rapid, natural drying of the straw after rain and uniform distribution of the ash.