(a) What is greenhouse effect? Write in detail about various greenhouse gases and their impact on crop production. (20 marks) (b)…

The greenhouse effect refers to the physical process wherein atmospheric trace gases absorb outgoing long-wave terrestrial infrared radiation and re-radiate it toward Earth, maintaining global thermal equilibrium.

Greenhouse Gases (GHGs) and Crop Production

Anthropogenic emissions have intensified radiative forcing through key GHGs: Carbon Dioxide (CO₂, Global Warming Potential [GWP] = 1), Methane (CH₄, GWP = 28, primarily from flooded rice paddies), Nitrous Oxide (N_2O, GWP = 273, from synthetic nitrogen fertilizers), Tropospheric Ozone (O₃), and Chlorofluorocarbons (CFCs, GWP > 1000).

Elevated CO₂ induces a transient fertilization effect, increasing photosynthetic rates in C3 crops like wheat and rice, but higher temperatures accelerate dark respiration and photorespiration, reducing net biomass. Warming alters crop phenology by shortening the vegetative phase and inducing terminal heat stress, which leads to pollen sterility and poor grain filling. High surface O₃ causes foliar chlorosis and lipid peroxidation. According to ICAR-NICRA projections, an anticipated temperature rise of 1.5–2.0°C by 2050 increases vulnerability across the Indo-Gangetic Plains, threatening a 3–10% yield reduction in irrigated wheat, whereas C4 millets exhibit higher thermal and moisture resilience.

Technologies and Market Policies in Crop Diversification

Agricultural technologies act as primary supply-side enablers of diversification. Precision farming, sensor-based IoT, and micro-irrigation decouple crop choice from local groundwater abundance. Protected cultivation (polyhouses) allows commercial shifts toward high-value floriculture and olericulture. Additionally, marker-assisted breeding has delivered short-duration, drought-tolerant oilseeds and pulses, mitigating climatic risks.

Concurrently, market policies govern farmer adoption. Historically, open-ended Minimum Support Price (MSP) and assured procurement entrenched the ecologically unsustainable paddy-wheat monoculture in Punjab and Haryana. Policy realignments—such as expanding MSP to pulses and oilseeds, mission-mode millet promotion under the National Food Security Mission (NFSM-Shree Anna), and aggregation through Farmer Producer Organisations (FPOs) integrated with e-NAM—lower transaction costs and market risks. Comprehensive risk coverage under PM Fasal Bima Yojana (PMFBY) and targeted import-export tariffs further incentivize farmers to reallocate acreage toward high-value and climate-resilient alternatives.

Herbicide Activity and Selectivity

Herbicide activity describes the mode of action on plant physiology: contact herbicides (e.g., paraquat) destroy only the contacted foliar tissues by disrupting cell membranes, whereas systemic herbicides (e.g., glyphosate) translocate apoplastically through the xylem or symplastically through the phloem to reach subterranean and apical meristems.

Selectivity represents the differential toxicity between the crop and associated weeds, determined by three mechanisms:

1. Morphological Selectivity: Differences in plant architecture, leaf angle, and cuticular wax thickness dictate spray retention, protecting narrow, upright cereal leaves from broadleaf sprays.
2. Physiological Selectivity: Differential spatial translocation or localized adsorption confines the active compound away from vital metabolic sites.
3. Biochemical Selectivity: The ability of the crop to rapidly degrade or conjugate the herbicide into non-toxic metabolites via endogenous enzymes like glutathione S-transferases or cytochrome P450s.

In Indian agro-ecosystems, 2,4-D selectively eliminates dicot weeds in cereal crops, atrazine is safely metabolized by maize while controlling broadleaf competitors, pendimethalin serves as a selective pre-emergence herbicide in pulses and oilseeds, and glyphosate functions as a broad-spectrum, non-selective herbicide for total weed clearance in non-cropped areas.

A policy shift combining climate-resilient crop technologies, calibrated price incentives, and precision weed management is vital for sustainable intensification and long-term food security.