**3. What is agricultural burning?**

Agricultural burning is the intentional setting of fire in the open field for preparation of the land for the next crop or killing the weeds and insect pests. Natural causes such as lightening and planned anthropogenic fire account for only 10–20 per cent of the total open burning across the globe [12]. Burning of agricultural residues is different from fire in forests, grasslands or any vegetation.

### **4. Drivers of open burning of crop residues**

Slash and burn cultivation has been a traditional system in agriculture to clean up vegetation on virgin land and cultivate crops for a few years before shifting to a new area. Tradition, timing, ease, weather and location factors encourage the farmers to burn residues in many regions. Burning is the cheapest and quickest way of eliminating unwanted thrash from the crop fields. Addition of plant nutrients and killing of pathogens, insects and weed species also influence decision to burn residues *in-situ* [12]. Moreover, shorter sowing window for one or two weeks compels the farmers to remove crop residues through burning, especially in absence of alternative options for its productive and profitable disposal. So also, rising labour cost and their seasonal scarcity insist the farmers to burn residues *in situ*. However, absence of stringent punitive action very often fails to curb such open burning of crop residues.

### **5. Status of agricultural burning in the world and India**

Burning of crop residues *in situ* has been a traditional practice in many countries as it is the cheapest, easiest and quickest way of getting rid of such bulky materials

immediately before raising the succeeding crop. It also checks weed and pest infestation in the succeeding crop. More so over, it does not require much technical skill and expertise in doing so. This practice was widespread and popular across the globe until 1990s when many governments restricted open burning of crop residues. In China and England, stubble burning is banned but in Australia, it is restricted to only need-based burning. In America and Canada, residue burning is still allowed in some counties and provinces. China, India and America are in the forefront of burning of crop residues followed by Brazil, Indonesia and Russian federation. Some African countries have top rated in the global ranking of intensive burning per hectare. Mexico and Tanzania are at the top position in intensive burning followed by Brazil, United States and Nigeria [12]. Globally, 24 per cent of the burnt residues are from rice, 23 per cent from wheat, 5 per cent from sugarcane and 48 per cent from maize [12]. An estimate in 1985 indicated burning of 2060 Tg of biomass in the developing world; of this, Asia, Africa and Larin America contributed 66, 21 and 13 per cent, respectively [13].

Large scale burning of paddy stubbles in Punjab, Haryana and western Uttar Pradesh in India in the month of late October and November every year is estimated to be 35 Mt. This practice is spreading to other parts of the country like wildfire due to the advent of precision farm-equipments that allow resowing with the minimum soil disturbance. The crop field is made ready for the succeeding zero till wheat crop by burning of straw and stubbles leftover in the field from the crop harvested by combined harvester. India generates around 500 Mt. of residues from rice, wheat, sugarcane, maize, millet and other crops every year [14] of which 142 Mt. are


#### **Table 2.**

*Agricultural waste generation in India and adjacent countries [15–17].*

#### **Figure 1.**

*NASA Earth Observatory image of the aerosol pollution in India, Pakistan and Nepal on 7 November 2017 [21].*

leftover after fuel, fodder and industrial uses [15] and 92 Mt. are burnt every year across the country. **Table 2** compares the agricultural wastes generated in India and its adjacent countries which reveal that the volume of waste is far more than the total waste generated by other countries.

Near about 70 per cent of crop residues in India are cereals of which 34 per cent come from rice, and 22 per cent from wheat crops [14]. Estimation indicated burning of about 80 per cent of the total 20 Mt. of rice stubble in Punjab alone [14]. Whereas another estimate indicated 9.8 and 1.23 Mt. of rice residue-burning in Punjab and Haryana, respectively [18]. Burning of rice is more compared to wheat in the North West India as rice contains more silica (12–16 per cent vs. 3–5 per cent) which is not easily digestible. About 75 per cent of wheat straw is collected and stored as fodder. Rice stem contains lower silica than leaves and hence rice is to be cut as close to ground if used for feeding animals [19]. Management of rice straw is difficult compared to wheat due to shorter window for sowing of wheat and low temperature which compels the farmers to resort to burning during October–November every year [20]. Several major cities of North India—including New Delhi, Lucknow, and Kanpur—faced elevated levels of aerosol pollution [21]. The extent of aerosol pollution in India, Pakistan and Nepal region, mostly from crop residue burning, can be observed from the captured image of the NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) on Aqua satellite on 7 November 2017 (**Figure 1**).
