(a) Explain the term conventional and conservation tillage. Give account of their comparative effects on soil properties and…

(a) Conventional vs. Conservation Tillage Conventional tillage involves intensive soil manipulation (mouldboard or disc ploughing followed by harrowing) that inverts and pulverises the soil, buries residues and prepares a clean seedbed. Conservation tillage (CT) is any system that leaves at least 30% of the soil surface covered with crop residue after sowing, by reducing or eliminating tillage: zero/no-till, strip-till, ridge-till and reduced tillage (for example, zero-till wheat sown with a Happy Seeder into rice residue in the Indo-Gangetic plains).

Comparatively, conventional tillage loosens the surface soil for a while but breaks aggregates, leaves the soil bare to crusting and erosion, and forms a compacted plough pan below the tillage depth, reducing infiltration and increasing runoff. CT may leave a slightly higher surface bulk density, but it builds stable aggregates and continuous biopores (root channels, earthworm burrows), so infiltration, moisture retention and soil biological activity improve. CT also tends to raise surface organic carbon; by reducing oxidation of soil organic matter, it acts as a carbon sink, potentially sequestering 0.1–0.5 t C/ha/year. Regarding Green House Gas (GHG) emissions, conventional tillage releases significant CO2 from accelerated decomposition and increases N2O via nitrification-denitrification cycles due to exposed soil. CT reduces fuel-based CO2 emissions by 50–70% due to fewer tractor passes. Furthermore, CT improves soil microbial biomass and enzymatic activity, fostering a healthier rhizosphere. The balance is not one-sided: in poorly drained or wet soils no-till can increase N₂O emission, and much of the carbon gain is concentrated in the top few centimetres. No-till upland soils often oxidise more methane (CH₄) because of better soil structure, though this varies with soil type.

(b) Remote Sensing for Ecosystem Analysis and Drought Remote sensing provides spatially explicit data for ecosystem analysis using optical, thermal, and microwave sensors. Optical sensors like Landsat, Sentinel-2 and India's Resourcesat (LISS-III, AWiFS) capture reflected radiation to calculate vegetation indices. The Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) quantify greenness and canopy density. Leaf Area Index (LAI) is derived from these indices or radiative transfer models, serving as a critical structural parameter. Light-use efficiency models then utilize LAI as an input, along with radiation data, to estimate Net Primary Productivity (NPP), thereby modeling ecosystem productivity. Microwave sensors (SAR) penetrate cloud cover, providing all-weather data on soil moisture and biomass.

For drought monitoring, remote sensing integrates meteorological and biophysical data. The Standardized Precipitation Index (SPI) quantifies precipitation deficits. The Vegetation Condition Index (VCI) compares the current NDVI with its historical range, while the Temperature Condition Index (TCI) does the same for land-surface temperature; both flag vegetation stress. In India, the National Agricultural Drought Assessment and Monitoring System (NADAMS) (now run by the Mahalanobis National Crop Forecast Centre) combines these remote sensing indices with rainfall and sown-area data to give fortnightly district-level assessments of agricultural drought during the season, which support drought declaration and contingency planning.

(c) Weed Control in Black Gram and Sesame Black Gram (Vigna mungo) has a critical weed-free period of 15–30 days after sowing (DAS). Major weeds include Trianthema portulacastrum and Digitaria sanguinalis. Management involves cultural practices like optimal seed rate and spacing to accelerate canopy closure. Mechanical control requires one hand weeding at 20 DAS. Chemical control employs pre-emergence pendimethalin (0.75–1.0 kg a.i./ha within 2–3 DAS), followed where needed by post-emergence imazethapyr (about 50–75 g a.i./ha at 15–20 DAS) for broadleaf and grassy weeds, or quizalofop-ethyl for grasses.

Sesame (Sesamum indicum) exhibits slow initial growth, making it highly susceptible to weeds like Cyperus rotundus and Portulaca oleracea. The stale seedbed technique, involving pre-sowing tillage to germinate weeds followed by a second tillage, is effective. Mulching suppresses weeds and conserves moisture. Hand weeding is required twice, at 20 and 40 DAS. Pre-plant incorporation of fluchloralin (about 1.0 kg a.i./ha) or pre-emergence pendimethalin or alachlor (0.75–1.0 kg a.i./ha) provides early control; thinning and weeding at 15–20 DAS keeps the crop clean through its critical period, all within an Integrated Weed Management (IWM) approach.