(a) Discuss the response of crop plants to rising temperature and carbon dioxide levels in relation to climate change, with…

(a) Crop response to rising temperature and CO₂

Elevated CO₂ raises photosynthesis in C3 crops such as wheat, rice and soybean by suppressing RuBisCO oxygenation (photorespiration) and improves water-use efficiency through partial stomatal closure. C4 crops (maize, sorghum, pearl millet) gain little, because their CO₂-concentrating mechanism is nearly saturated at ambient levels, though they benefit in drought through water savings. Grain protein and micronutrient (zinc, iron) concentration tend to fall under high CO₂.

Higher temperature offsets these gains. It speeds phenology and shortens the vegetative and grain-filling periods, causing terminal heat stress in rabi wheat (yield loss of roughly 3–4% per 1°C rise above the optimum), as seen in the 2022 March heat wave. Heat at anthesis causes spikelet sterility in rice above about 35°C and poor pod set in legumes. Adaptation needs heat-tolerant cultivars, earlier sowing and mulching.

(b) Speciality corn in cropping systems

Speciality corns are sweet corn, baby corn, popcorn and quality protein maize (QPM). Baby corn (about 50–60 days to harvest) and sweet corn (65–75 days) are short-duration, so they fit between main crops in sequences such as baby corn–potato–greengram, and three to four crops a year lift cropping intensity above 250%.

They can also be intercropped with cowpea or greengram for a better land-equivalent ratio and soil fertility. Profitability rises because green cobs sell fresh or to processors at much higher prices than grain maize, popcorn and QPM support value-added chains, and the green stover and husk give nutritious fodder that cuts livestock costs. Peri-urban fields near markets, contract arrangements with processors and farmer-producer organisations give the best returns.

(c) Non-wood forest products and local development

Non-wood forest products (NWFPs), also called minor forest produce, are goods of biological origin other than timber taken from forests: bamboo, cane, tendu leaves, lac, gums and resins, honey, mahua flowers, medicinal plants, mushrooms and tree-borne oilseeds.

They give forest-dwelling communities cash and subsistence; estimates put their share at 20–40% of tribal household income, and they fill the lean agricultural months with collection, grading and processing work, done mostly by women. The Forest Rights Act 2006 and PESA 1996 give communities rights over minor forest produce, the Minimum Support Price for Minor Forest Produce scheme (2013) offers price support, and the Pradhan Mantri Van Dhan Yojana (TRIFED, 2018) forms Van Dhan Vikas Kendras for value addition. These reduce middlemen exploitation and distress migration and encourage conservation.

(d) Cultural and chemical weed control in soybean and wheat

Soybean. Cultural: stale seedbed or a pre-sowing tillage pass, 45 cm × 5 cm spacing for early canopy closure, intercropping with maize or pigeonpea, and hand weeding at 20 and 40 days after sowing (DAS). Chemical: pre-emergence pendimethalin at 1.0 kg a.i./ha within 48 hours of sowing, then post-emergence imazethapyr at 75–100 g a.i./ha at 15–20 DAS for grasses and broadleaves such as Echinochloa colona and Trianthema portulacastrum.

Wheat. Cultural: closer rows (18–20 cm), zero tillage with residue mulch using a Happy Seeder, timely sowing, and rotation with mustard or chickpea to break Phalaris minor cycles. Chemical: post-emergence sulfosulfuron at 25 g a.i./ha or clodinafop-propargyl at 60 g a.i./ha at 30–35 DAS for P. minor, and metsulfuron-methyl at 4 g a.i./ha or 2,4-D ethyl ester at 0.5 kg a.i./ha for broadleaves such as Chenopodium album and Rumex dentatus. Rotating modes of action avoids herbicide resistance.

(e) Genesis of soil structure and its significance

Soil structure is the arrangement of sand, silt and clay into aggregates or peds. It forms in two steps: flocculation of clay by divalent cations (Ca²⁺, Mg²⁺) and organic matter, then cementation and binding. Wetting–drying and freezing–thawing cracks the soil into peds; iron and aluminium oxides and carbonates cement them; roots and earthworms compact and bind particles; and fungal hyphae, glomalin and microbial polysaccharides stabilise micro-aggregates into water-stable macro-aggregates (Tisdall and Oades). Types include granular, blocky, platy and prismatic, and tillage and organic matter management influence them.

For crops, good granular or crumb structure balances macropores (aeration, drainage) and micropores (available water), lowers bulk density and root resistance, improves infiltration and nutrient diffusion, and resists crusting and erosion, raising seedling emergence and yield.