(a) Discuss the primary pathways of gaseous nitrogen losses from soil and the factors affecting nitrogen losses. (20 marks) (b)…

Gaseous Nitrogen Losses

Nitrogen losses from soil occur primarily through volatilization, denitrification, and chemo-denitrification. Ammonia volatilization is the conversion of ammonium (NH₄⁺) to ammonia gas (NH₃), driven by high soil pH, temperature, and the application of urea or ammonium-based fertilizers. Denitrification is the microbial reduction of nitrate (NO₃⁻) to gaseous forms (N₂, N_2O, NO) under anaerobic conditions. This process is favored by high soil moisture, low oxygen tension, and a high C:N ratio in organic matter. Chemo-denitrification involves the abiotic reduction of nitrite to nitric oxide, often occurring in acidic soils. Key factors influencing these losses include soil texture (clay soils retain more water, promoting denitrification), temperature (higher rates in warm seasons), and tillage practices (no-till systems may reduce volatilization but can increase denitrification in waterlogged zones).

Groundnut Cultivation

(i) Nutrient Roles Groundnut requires balanced nutrition. Nitrogen supports vegetative growth, though excess N reduces biological fixation. Phosphorus is critical for root development and energy transfer. Potassium enhances pod filling and oil content. Sulfur is vital for protein synthesis, while Magnesium is central to chlorophyll. Calcium is uniquely important for pod wall development and shelling percentage. Micronutrients are equally crucial: Molybdenum is essential for nitrogenase activity in root nodules; Boron ensures pollen viability and pod set; Zinc aids in enzyme function; Iron, Manganese, and Copper support photosynthesis and respiration. Deficiencies in Indian soils, particularly in micronutrients like Zn and B, often limit yields.

(ii) Pegging Pegging is the geotropic growth of the gynophore (peduncle) after fertilization. The peg grows downward into the soil, where it swells to form the pod. This process is highly sensitive to soil physical conditions. Soil crusting, compaction, or excessive moisture impedes peg penetration, leading to "blind pods" or reduced yield. Loose, friable soil is essential for successful pegging.

(iii) Irrigation Stages Critical irrigation stages are pegging (20-30 DAS), flowering (30-45 DAS), and pod development (50-60 DAS). Moisture stress during pegging reduces peg formation, while stress during pod development lowers shelling percentage and kernel weight. Drip irrigation is increasingly adopted in Gujarat and Tamil Nadu to maintain optimal soil moisture without waterlogging.

(iv) Weed Management Weeds compete for nutrients and light, particularly in the early stages. The critical weed-free period is 30-45 days after sowing (DAS). Integrated weed management includes pre-emergence herbicides like pendimethalin or fluchloralin, followed by post-emergence applications if necessary. Intercropping with cereals or legumes can also suppress weeds through canopy closure.

(v) Cropping Systems Region-specific systems optimize resource use. In Gujarat, kharif groundnut is often followed by rabi wheat or pulses. In Tamil Nadu, rice-groundnut rotation is common, leveraging residual moisture. In Andhra Pradesh, groundnut-redgram intercropping is prevalent, especially in Rayalaseema for rabi groundnut. These systems enhance soil health and economic returns.

GIS-Based Mapping

GIS-based soil mapping utilizes digital soil mapping (DSM) techniques, integrating remote sensing data, topography, and parent material to create detailed soil maps. In India, initiatives like the National Bureau of Soil Health and Plant Nutrition (NBSH) use GIS for soil health card distribution. Yield mapping is achieved through GPS-enabled combine harvesters that record yield data at specific locations. This data, integrated with NDVI (Normalized Difference Vegetation Index) from satellites, identifies spatial variability in productivity. Site-specific management, such as variable rate application of fertilizers, is then implemented to correct deficiencies and optimize yields. This precision agriculture approach enhances nitrogen use efficiency and sustainability in groundnut belts.

Conclusion

Sustainable groundnut production requires a holistic approach that minimizes gaseous nitrogen losses through efficient fertilizer management and leverages biological nitrogen fixation. Integrating precise nutrient management with GIS-based site-specific interventions ensures that resources are applied where needed, maximizing yield while minimizing environmental impact. This synergy between agronomy and technology is key to the future of Indian agriculture.