S.K. Jalota

WATER AND NITROGEN-BALANCE AND -USE EFFICIENCY IN A RICE (ORYZA SATIVA)-WHEAT (TRITICUM AESTIVUM) CROPPING SYSTEM AS INFLUENCED BY MANAGEMENT INTERVENTIONS: FIELD AND SIMULATION STUDY

SUMMARY The present study concerns identification of the most profitable and water and nitrogen use efficient best management practice (BMP) in a rice–wheat system using a combined approach of field experimentation and simulation. In the field study, two independent experiments, (1) effect of three transplanting/sowing dates, two cultivars and two irrigation regimes and (2) effect of four nitrogen (N) levels with four irrigation regimes, were conducted for two seasons of 2008–09 and 2009–10 at Punjab Agricultural University, Ludhiana, India. Integrating the treatments of the two independent field experiments, simulations were run with the CropSyst model. The BMP demonstrated was transplanting of rice on 20 June and sowing of wheat on 5 November, irrigation to rice at 4-day drainage period and to wheat at irrigation water depth/Pan–E (open pan evaporation) ratio of 0.9, and fertilizer N of 150 kg ha−1 to each crop for medium-duration varieties. This practice gave higher profit (35%), equivalent rice yield (16%), crop water productivity (15%), irrigation water productivity (51%), economic water productivity (34%) and economic N productivity (94%) than the existing practice by the farmers. The improvement in crop water productivity by shifting the transplanting/sowing date was due to reduction in soil water evaporation and increased transpiration and fertilizer N productivity through increased N uptake.

Yield, water use and root distribution of wheat as affected by pre-sowing and post-sowing irrigation.

Abstract Irrigation water is a limited resource, and therefore irrigation practices must be rationalized for high water-use efficiency. Little is known about the influence of stored water in deep soils on the water needs and the post-sowing irrigation requirements of crops. A 3-year field experiment was conducted to determine the effects of combinations of light and heavy pre-sowing irrigations with two post-sowing irrigation regimes on yield, root growth, water use and water-use efficiency of wheat on a deep alluvial sandy loam soil. Post-sowing treatments consisted of (i) five 75-mm irrigations at five growth stages, and (ii) irrigations based on pan evaporation, i.e. at IW/PAN-E ratio of 0.75 (75 mm of irrigation water were provided as soon as the open-pan evaporation minus rainfall since previous irrigation was 100 mm). The latter regime required 175 mm less water than that with irrigation at growth stages. Profile water utilization was inversely related to post-sowing irrigation water. Where pre-sowing irrigation was light, post-sowing irrigations based on pan evaporation yielded significantly less than those based on growth stages. With heavy pre-sowing irrigation, irrigation based on the pan evaporation yielded as much as five irrigations at growth stages. The former decreased the mean water application by 153 mm and increased the water-use efficiency by 26%. Irrigation based on pan evaporation stimulated greater utilization of stored water by increasing the rooting density in deeper layers. It is indicated that for higher water-use efficiency and yield, wheat should be sown after a heavy pre-sowing irrigation, and post-sowing irrigation should be based on 0.75 pan evaporation.

Climate Change Projections

This chapter illustrates global climate models, their downscaling (statistical and dynamical) and uncertainties due to initial conditions, boundary conditions, observations, model parameters and structure, and temporal variation depending upon the choice of point on the control run (baseline) for better understanding of climate change projections. It provides a detailed description of different emission scenarios from Special Report on Emission Scenario to Representative Concentration Pathways. It also covers the methods to minimize bias in the projected climate data by bias correction methods and uncertainties by performing ensemble simulations to have a more robust estimate of the climate change. Trends and magnitudes of climate change in the past and their projections in the future at global, regional, and local scale are also discussed.

Emission of Greenhouse Gases and Their Warming Effect

This chapter covers the main sources, processes, and factors controlling formation and emission of greenhouse gases (GHGs) from agricultural system, methods of their measurement in the field (static and closed chambers and micrometeorological methods), and estimation (from empirical relations and mechanistic models). It provides the details of the processes like mineralization and mobilization, nitrification, denitrification, volatilization, leaching, and runoff for nitrous oxide emission; biomass burning, tillage and soil disturbance, deforestation, draining of wetlands, uncontrolled grazing, and manufacturing fertilizers and pesticide for carbon dioxide emission; and methanogenesis of methane gas emission and its transport by diffusion, ebullition, and plant mediation along with their cycles in soil-plant-atmosphere continuum. The role of atmospheric, plant, and soil parameters and management interventions and feedback of climate change on GHG emission are also elucidated besides the potential global warming, radiative forcing, and lifetime of GHGs in the atmosphere.

Climate Change Impact on Crop Productivity and Field Water Balance

This chapter covers the fundamentals of direct and interactive effects of climate variables (carbon dioxide, temperature, and precipitation) in the changing climate scenario on soil environment (carbon pools, microbial population and diversity, nutrient availability, and soil water) and processes in plant (photosynthesis, respiration, transpiration, crop duration, and phenology) to understand their impact on yield and quality of agricultural crops, field water-balance components and water-use efficiency. With the support of on-hand experimental and simulation studies, this chapter also elucidates how direct and interactive effects of climate variables are modified by photosynthetic pathway (C3 and C4) and N-fixing capability (legumes and nonlegumes) of the crop, water regime, and nitrogen level in the soil.

Adaptation and Mitigation

This chapter covers the adaptation technologies to combat the climate change impact on crop production and mitigation strategies to minimize greenhouse gas (GHG) emissions in agriculture. The adaptation technologies explained are adjusting transplanting date, creating heat tolerance in plants for reducing temperature impact, straw mulching for conserving soil moisture, application of balanced fertilizers, and plant management for making the plants competent to tolerate volatile weather conditions. It also enlightens means to reduce GHG emissions such as using solid organic N fertilizers, tightening the N cycle, minimizing fallow and bare soil emissions, and using slow-release N fertilizers for nitrous oxide; sequestering carbon, reducing soil disturbance, practicing organic farming, and growing cover crops for carbon dioxide; and proper management of fertilizer (using -containing N and compost and applying N fertilizers as foliar spray), irrigation water (mid-season drainage or alternate wetting and drying), and crop (growing upland crops and selecting rice cultivars that have high root oxidative activity) for methane.

Climate Change and Groundwater

This chapter aims at understanding the impact of increased CO 2 , temperature, and P cp due to climate change on hydrologic cycle components, such as evapotranspiration (ET), runoff, recharge and discharge, and quality change of groundwater. Methodologies to measure recharge, discharge, and fluxes across boundaries are also talked about. It comprises information on the effect of land use and land cover, vegetation, and geology of the aquifer on recharge. Emission of gases due to energy is expended on groundwater pumping, groundwater estimation by coupling climate, soil-water-crop, and groundwater models through geographic information system (GIS). The management interventions of enhancing the surface-water supply and reducing groundwater draft to protect the groundwater resources from the impact of climate change are also discussed.