**6. Legal implications**

Agriculture comes under the state list of the Seventh Schedule of the Constitution of India and hence, the State Governments have to take austerity measures against residue burning. Burning of crop residues is a crime in India according to the Air Pollution Act, 1981 and Section 188 of the Indian Penal Code [14]. Courts in India have banned open burning of crop residues and made provisions of penal actions by collecting fines from the errant farmers. In 2018, the national green tribunal (NGT) of India imposed penalty of Rs.2,00,000 on the Delhi government for not filing an action plan for incentives and infrastructural assistance against stubble burning [22]. Subsequently, the NGT asked the Delhi government to deposit 250 million rupees (INR) with the Central Pollution Control Board (CPCB) as performance guarantee [23]. Consequent up on Public Interest Litigation in M. C. Mehta vs. Union of India (order IA No.158129 and 158129 of 2019 in writ petition (C) No.13029 of 1985) [24] an ordinance dissolving the Environment Pollution (Control and Prevention) Authority has been passed by the Indian government to set up a new Commission with over 20 members to regulate pollution in Delhi-NCR region [25]. In this ordinance, the Ministry of Law and Justice has made provisions for imprisonment up to five years or with fine up to rupees one crore or both for abrogation of the rule/provisions or order/directions of the Commission [25]. The Hon'ble Supreme Court of India has also realized the need for incentives to small and marginal farmers those abiding to the rules by paying a sum of Rs.100 per quintal of crop residues [24].

In the United States, agricultural burning policy has been formulated to monitor open burning of agricultural wastes and weeds for fire, weed and pest control adjacent to the crop field so as to allow regulated burning in small scale to maintain agricultural production but without impairing public health and air quality parameters. The agricultural burning managers are authorized to monitor burning at state, local and tribal level and no burning should be carried out without approval from the competent authority [26].

**Figure 2.** *Open burning of rice straw before land preparation for second rice crop in Bargarh district of Odisha.*

#### **7. Environmental impacts of open crop residue burning**

Cereals generate huge agriculture as well as agri-industrial wastes across the globe. If not managed judiciously then in long run, that may lead to the environmental pollution and global warming. Open burning of agricultural wastes is detrimental to both environment and human health. Poisonous gases like carbon dioxide (CO2), carbon monoxide (CO), sulfur oxides (SOx), nitrogen oxides (NOx), methane (CH4) and particulate matters (PM2.5 and PM10) are released into the atmosphere (**Figure 2**). An estimate reveals burning of crop residues release 149.24 Mt. of CO2, 9 Mt. of CO, 0.25 Mt. of SOx, 1.28 Mt. of PM and 0.07 Mt. of black carbon [14]. The situation is austere in India due to intensive rice-wheat cropping system [27]. One ton of stubble burning leads to the loss of 5.5 kg nitrogen, 2.3 kg phosphorous, 25 kg potassium and 1 kg sulfur besides organic carbon [14]. As per an estimation, stubble burning releases substantial quantity of heat that elevates the surface temperature from 33.8 to 42.2°C killing soil fertility maintaining biota [14]. The population of microorganisms, earthworms and beetles get reduced drastically in the upper layer of soil affecting the rate of soil formation. The population of beneficial insects reduces drastically and the enemy inset population increases to a great extent.

Stubble burning increases the particulate matters in the air creating pulmonary diseases (COPD), bronchitis, lung capacity loss, emphysema, cancer, etc. [27] in humans and animals besides irritation in eyes, nose and throat [14]. The Ministry of Earth Sciences' monitoring agency SAFAR in Delhi has estimated the share of stubble burning in PM2.5 pollution as high as 36 per cent [28]. In Punjab (India) alone an estimated 760 million rupees (INR) is spent annually to alleviate stubble burning related diseases [27]. The Energy and Resources Institute (2019) reported 5 million deaths in South Asia in 2012 due to air pollution which was around 22 per cent of the total deaths in the region [27].

#### **8. Agri-waste management options**

The crop stubbles and agricultural wastes, if managed properly, could generate profits to the farmers and protect the environment from the severe pollution as well. Some of the available alternative management practices include soil incorporation, compost and biochar making, thermal power generation, pulp and *Sustainable Biowaste Management in Cereal Systems: A Review DOI: http://dx.doi.org/10.5772/intechopen.97308*

paper manufacturing, cement brick making, mushroom production, or biofuel production (**Figure 3**) [27]. However, most of the farmers in North India are not yet fully aware of many such alternatives that lead to *in-situ* open burning of crop residues.

### **8.1 Residue incorporation**

Since long back, *in-situ* incorporation of crop residues has been the simplest, easiest, quickest and cheapest technique of agri-waste management next to open burning. Rotavators, soil turning or mould board ploughs, and puddlers are most effectively and widely used these days to shred down larger plant parts and to incorporate into the soil. Rotavator, a low cost precision implement of around 0.1 to 0.12 million rupees (INR) with the working efficiency of 5–6 hectares per day is suitable for both *kharif* and *rabi* crops. Residue incorporation improves soil bio-physicochemical properties and increases crop productivity as well. Rotavator readily and economically incorporates biomass of weeds and green manuring crops as manual removing or chopping and mixing would cost higher [29].

Incorporation of maize crop residues in clayey Andosol in Ethiopia at 6 Mg per hectare for consecutive three years indicated 22–52 per cent reduction in penetration resistance in top 5–10 cm soil, 39–57 per cent lower evaporative flux and elevated (22 per cent) macro and meso porosity [30]. After 17–18 cycles of residue incorporation in rice-wheat system, the mean weight diameter (MWD) of water stable aggregates, bulk density (BD), and water holding capacity (WHC) of soil increased [31].

Crop residues on the soil surface protect the soil from erosion, act as mulch that keep the soil cool and improves soil tilth [32]. In the USA, near about 40 per cent cropland are under no till farming with minimal investment and more than 10 M ha has been sown under cover crops with basic objectives to incorporate residues *in situ* and regenerate crop without tillage [32]. In Indo-Gangetic plain of India, mulching with the preceding rice residues has been a good agronomic practice in absence of tillage that increases soil organic carbon in long run, WHC, water use efficiency and profitability in wheat [33]. Surplus residues of the wheat crop can also be incorporated into the next rice crop with improvement in physical, chemical and biological properties of the soil [33].

Rapid reduction in the soil organic carbon (SOC) across the globe due to intensive monocropping without biomass incorporation has been the greatest challenge before us in this 21st century. With the changing climate and advent of chemical farming, the role of soil in maintaining the ecosystem services has brought forth so many issues and if left unattended may end in peril. About 29 and 60 per cent increase in carbon stocks in silt-loam and clayey soil in top 20 cm soil whereas the effect was seen in the upper horizon only in sandy soil has been reported [34].

Residue incorporation needs energy and time. Extra N at the time of incorporation is needed for preventing temporary immobilization of nutrients (mostly N) and correcting high C:N ratio of substrates [35]. The rate of immobilization lasts for four to six weeks under favorable soil type, moisture and temperature conditions and management factors. Starter N dose of 15 to 20 kg ha−1 could very well increase the yield of succeeding wheat or rice crop without any adverse effect on the next crop. Wheat yield depression of 0.54 to 0.08 t ha−1 has been reported with soil application of 60 and 180 kg N ha−1, respectively [36]. However, release of greenhouse gases such as CO2 and CH4 that leads to global warming can also not be set aside. Incorporation of cereal straw (having wide C:N ratio) with green manure (having narrow C:N ratio) facilitates decomposition before rice transplanting. Wheat yield reduction in initial 2 to 3 years of rice straw incorporation a month before wheat planting were although reported but in subsequent years, straw incorporation had no significant adverse effect on wheat yield. Rather, wheat yield increased by 0.6 t ha−1 over 2.91 t ha−1 with straw removal [36]. In contrast, yield advantage in wheat sown after 3 weeks of rice straw incorporation was reported in clay loam soil but not in sandy loam soil. After incorporation of rice straw, about 10–20 per cent of it is assimilated by the rice crop itself, 10–20 per cent is lost to the atmosphere through various pathways and 60 to 80 per cent is immobilized in soil [36]. Nutrient up to 40 kg ha−1 could be harnessed through incorporation of 10 t of rice straw 4 to 5 weeks before transplanting of rice in the main field [36]. Residue incorporation increases soil N and available P and K [36]. Long-term comparative studies on wheat crop residue incorporation versus inorganic fertilizer application in India showed significantly higher yield in rice and wheat through inorganic nutrition but in subsequent years, the yield under residue incorporation plus inorganic fertilizer was at par with sole inorganic one. In the fourth year, the combined mode of nutrition out-yielded the inorganic one [36].

#### **8.2 Composting**

Composting is the method of aerobic or anaerobic decomposition of organic solid wastes. It is not new; rather, it has been the oldest practice of recycling the plant nutrients in the soil. Small scale backyard composting is a usual practice in many developing and underdeveloped countries. Up till now, composting had not gained the status of agriculture industry. But with the gaining popularity of organic farming or eco-farming, its demand has increased these days. Its bulkiness, low nutrient content and high labour requirement are the major challenges in undertaking such organic waste composting projects. However, on-site composting without transportation of crop residues could be the befitting answer for maintaining soil fertility and sustaining crop production in long run. Compost improves biophysiochemical properties of the soil while the need for synthetic fertilizers and plant protection measures could be eliminated completely. Its application improves nutrient uptake and cycling, soil microbial activity and biodiversity, and deficit moisture stress conditions as it regulates soil pH, improves soil texture, structure and aggregates, increases water holding capacity, cation ion exchange capacity and soil biodiversity [37]. It reduces soil erosion, protects crop against soil borne

diseases, increase carbon sequestration and reduce compaction [37]. Composting releases heat during thermophyllic stage that kills most of the pathogens, insect larvae and eggs, and weed seeds [37].

On decomposition, biomass turns into a humus like substance called compost. The rate of compositing depends on the type of substrate and microbes, ambient air temperature, moisture level, aeration, presence or absence of toxic chemicals and heavy metals and surface area of the residue. Aerobic decomposition releases CO2 and H2O while anaerobic composting releases CH4.

$$\text{C}\_6\text{H}\_{12}\text{O}\_6 + 6\text{O}\_2 \rightarrow \text{CO}\_2 + \text{H}\_2\text{O} + \Delta\text{E}\left(\text{3,880 kJ mol}^{-1}\right) \qquad \text{Aerobic decomposition}$$

$$\text{C}\_6\text{H}\_{12}\text{O}\_6 + 2\text{H}\_2\text{O} \rightarrow \text{CO}\_2 + \text{H}\_2\text{O} + \Delta\text{E}\left(405\text{ kJ mol}^{-1}\right) \quad \text{Anaeerobic decomposition}$$

The total carbon and nitrogen (C:N) ratio of the substrate is important for deciding the rate of decomposition of organic matter. Higher the ratio then longer is the duration for degradation. The desired C:N ratio for decomposition is 24:1 [38]. This 24 part of carbon is divided into 16 parts for energy and 8 parts for microbial body as most microbes have a body with C:N of 8:1 [38]. When C:N ratio exceeds 24 then microbes explore other available sources with moderate ratio. Immediately after addition of biomass, the microbial population increases resulting in immobilization i.e. transformation of N from available form to non available form. When these microbes die and decompose, the N mineralizes and becomes available for crop removal. Cereals have higher C:N ratio than legumes and hence, legumes decompose faster [38]. The **Table 3** depicts C:N ratio of different agricultural crops.

The C:N ratio changes with stage of the crop. It also differs in different plant parts and with the progression of decomposition [38]. Cereals take longer period for composting that can be reduced by mixing with legumes or supplementing nitrogenous fertilizers. In compost pits cereal substrates are put in alteration with the vegetables or pulse residues. For example, rice straw and grass put together resulted in the highest rate of vermicompost production at the end of 120 days cycle compared to either of these substrate composted separately [39]. Similarly, [40] suggested addition of food stuff with rice bran for getting superior vermicompost with average C:N ratio of 20.85, 183.3, 16.86 and 15.16 from 1:1, 1:2, 1:3 and 1:5 ratio of rice bran: food stuff, respectively.

Crop residues are used for vermicomposting, enriched composting, farm yard manure, etc. Vermicomposting is the biological degradation of substrates by combined action of earthworms and microorganisms. Windrows method of vermicomposting is popular and widely practiced by adding rice straw, animal manure, and


#### **Table 3.** *C:N ratio of different agricultural crops at harvest [38].*

shredded banana trunks and maintaining the moisture at 60 per cent [41]. Tank, pit or heap method of vermicomposting can be followed as per convenience and quantity of available residues to be managed. Spent straw from mushroom farm containing C and N of 14.3 and 0.7 per cent can also be recycled through composting [41]. *Eisenia fetida* is the most widely used species of earthworm for vermicomposting in many parts of the world. However, *Lampito mauritii*, *Lumbricus rubellus*, *Eudrilus eugeniae* and *Perionyx excavates* are also inoculated depending on the purpose of composting, availability of culture and ecological conditions.

Unlike open burning, composting preserves essential plant nutrients and almost all nutrients remain inside the compost. Only the loss of N occurs in form of ammonia and nitrous oxide due to volatilization [42]. As much as 75 per cent of total N in manure is lost in form of NH3 and 1.5 to 7.3 per cent in form of N2O [43, 44]. Most composts do not contain more than 2 per cent N and its release depends on the C:N ratio, soil temperature, moisture and microbial activity [44]. Composts are better supplements for crop plants unlike most chemical fertilizers that are devoid of trace or micronutrients. The CHNS analyses of rice straw and its compost revealed increase in oxygen, sulfur and moisture but reduced total organic carbon, hydrogen and nitrogen [45]. Application of effective microorganisms (EM) to composting rice is reported to have increased macro and micronutrient content. The N, P and K content of the rice-compost is higher with EM and the Fe content was significantly higher without significant increase in Zn and Cu [46].

#### **8.3 Production of biochar**

Production of biochar or pyrogenic carbon was the age-old practice in the Amazonian river bank which was evident from the *Terra preta* culture to enrich soil and cultivate crops sustainably. Modern researchers are constantly looking for imbibing such technology to smother greenhouse gas emissions and increase carbon sequestration as well. The process of carbon sequestration needs higher residence time and resistance to chemical oxidation of carbon to carbon dioxide or methane [47]. Use of agricultural wastes for biochar-making could be a viable option in the era of massive deforestation and loss of habitats. Biochar is a porous fine-grained carbonaceous material released from thermo-chemical conversion of biomass called pyrolysis at relatively moderate temperature [48]. It contains carbon, hydrogen, oxygen, nitrogen, sulfur and ash. On its addition, the bio-physicochemical properties of the soil improve and crop yield enhances. Apart from agriculture-use, biochar is used in water treatment plant, food and cosmetic industry, metallurgy, construction industry and many more purposes.

Researchers have observed that the pyrolytic temperature of 400°C brings in high alkalinity, cation exchange capacity, high level of available P and exchangeable cation in rice straw biochar which is suitable for soil amendment and used as fertilizer [49]. At this temperature, rice straw biochar shows the largest Cu (II) absorption capacity (0.37 mol kg−1) that is mostly of non electrostatic absorption [50]. Corn stalk biochar can also be used as efficient absorber of Pb+2 [51] and Cd+2 [52]. Continuous application of rice straw biochar and rice straw has positive influence on soil physicochemical properties with 26.9 and 70.2 per cent increase in total porosity and air permeability [53]. Its application increases soil microbial biomass carbon and nitrogen [53] and increases wheat productivity and accumulate P in grain [54]. Corn cob biochar is reported to have increased the pH, organic matter, soluble and available K in calcareous sandy soil [55]. Maize straw biochar application to soil reduced harmful bacteria diversity but selectively promoted community of functional bacteria population [56]. The C sequestration capacity of corn stalk (0.26) was increased to 0.64 to 1.0 on charring as resistance of char to decomposition prohibits C losses during charring [57].
